Android Programming_ The Big Nerd Ranch Guide

【实例截图】

【核心代码】

Table of Contents
Learning Android ........................................................................................................... xix
Prerequisites .......................................................................................................... xix
What’s New in the Third Edition? ............................................................................. xix
How to Use This Book ............................................................................................. xx
How This Book Is Organized .................................................................................... xx
Challenges ..................................................................................................... xxi
Are you more curious? .................................................................................... xxi
Code Style ............................................................................................................. xxi
Typographical Conventions ...................................................................................... xxii
Android Versions ................................................................................................... xxii
The Necessary Tools ..................................................................................................... xxiii
Downloading and Installing Android Studio .............................................................. xxiii
Downloading Earlier SDK Versions ......................................................................... xxiii
A Hardware Device ............................................................................................... xxiv
1. Your First Android Application ........................................................................................ 1
App Basics ............................................................................................................... 2
Creating an Android Project ........................................................................................ 3
Navigating in Android Studio ...................................................................................... 8
Laying Out the UI ..................................................................................................... 9
The view hierarchy .......................................................................................... 13
Widget attributes ............................................................................................. 14
Creating string resources ................................................................................... 15
Previewing the layout ....................................................................................... 16
From Layout XML to View Objects ........................................................................... 17
Resources and resource IDs ............................................................................... 18
Wiring Up Widgets .................................................................................................. 21
Getting references to widgets ............................................................................. 22
Setting listeners ............................................................................................... 23
Making Toasts ......................................................................................................... 25
Using code completion ..................................................................................... 26
Running on the Emulator .......................................................................................... 27
For the More Curious: Android Build Process .............................................................. 30
Android build tools .......................................................................................... 31
Challenges .............................................................................................................. 32
Challenge: Customizing t
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Adding an Icon ....................................................................................................... 48
Adding resources to a project ............................................................................ 49
Referencing resources in XML .......................................................................... 51
Challenge: Add a Listener to the TextView .................................................................. 52
Challenge: Add a Previous Button .............................................................................. 52
Challenge: From Button to ImageButton ...................................................................... 53
3. The Activity Lifecycle .................................................................................................. 55
Logging the Activity Lifecycle .................................................................................. 57
Making log messages ....................................................................................... 57
Using Logcat .................................................................................................. 59
Exploring the activity lifecycle by example .......................................................... 60
Rotation and the Activity Lifecycle ............................................................................ 63
Device configurations and alternative resources ..................................................... 63
Saving Data Across Rotation ..................................................................................... 68
Overriding onSaveInstanceState(Bundle) .............................................................. 69
The Activity Lifecycle, Revisited ............................................................................... 70
For the More Curious: Current State of Activity Cleanup ................................................ 72
For the More Curious: Log Levels and Methods ........................................................... 73
Challenge: Preventing Repeat Answers ........................................................................ 74
Challenge: Graded Quiz ............................................................................................ 74
4. Debugging Android Apps .............................................................................................. 75
Exceptions and Stack Traces ..................................................................................... 76
Diagnosing misbehaviors .................................................................................. 78
Logging stack traces ........................................................................................ 78
Setting breakpoints .......................................................................................... 80
Using exception breakpoints .............................................................................. 83
Android-Specific Debugging ...................................................................................... 85
Using Android Lint .......................................................................................... 85
Issues with the R class ..................................................................................... 87
Challenge: Exploring the Layout Inspector ................................................................... 88
Challenge: Exploring Allocation Tracking .................................................................... 89
5. Your Second Activity ................................................................................................... 91
Setting Up a Second Activity .................................................................................... 93
Creating a new activity ..................................................................................... 93
A new activity subclass .................................................................................... 96
Declaring activities in the manifest ..................................................................... 97
Adding a cheat button to QuizActivity ................................................................ 98
Starting an Activity .................................................................................................. 99
Communicating with intents ............................................................................ 100
Passing Data Between Activities ............................................................................... 101
Using intent extras ......................................................................................... 102
Getting a result back from a child activity .......................................................... 105
How Android Sees Your Activities ............................................................................ 109
Challenge: Closing Loopholes for Cheaters ................................................................ 112
6. Android SDK Versions and Compatibility ....................................................................... 113
Android SDK Versions ........................................................................................... 113
Compatibility and Android Programming ................................................................... 114
A sane minimum ........................................................................................... 114
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Minimum SDK version ................................................................................... 117
Target SDK version ........................................................................................ 117
Compile SDK version ..................................................................................... 117
Adding code from later APIs safely .................................................................. 118
Using the Android Developer Documentation ............................................................. 120
Challenge: Reporting the Build Version ..................................................................... 122
Challenge: Limited Cheats ....................................................................................... 122
7. UI Fragments and the Fragment Manager ....................................................................... 123
The Need for UI Flexibility ..................................................................................... 124
Introducing Fragments ............................................................................................ 125
Starting CriminalIntent ............................................................................................ 126
Creating a new project .................................................................................... 129
Two types of fragments ................................................................................... 130
Adding dependencies in Android Studio ............................................................ 131
Creating the Crime class ................................................................................. 134
Hosting a UI Fragment ........................................................................................... 136
The fragment lifecycle .................................................................................... 136
Two approaches to hosting .............................................................................. 137
Defining a container view ............................................................................... 137
Creating a UI Fragment .......................................................................................... 139
Defining CrimeFragment’s layout ..................................................................... 139
Creating the CrimeFragment class ..................................................................... 142
Adding a UI Fragment to the FragmentManager .......................................................... 148
Fragment transactions ..................................................................................... 149
The FragmentManager and the fragment lifecycle ................................................ 152
Application Architecture with Fragments ................................................................... 153
The reason all our activities will use fragments ................................................... 154
For the More Curious: Fragments and the Support Library ............................................ 155
For the More Curious: Why Support Fragments Are Superior ........................................ 156
8. Displaying Lists with RecyclerView .............................................................................. 157
Updating CriminalIntent’s Model Layer ..................................................................... 159
Singletons and centralized data storage .............................................................. 159
An Abstract Activity for Hosting a Fragment .............................................................. 161
A generic fragment-hosting layout .................................................................... 161
An abstract Activity class ................................................................................ 162
RecyclerView, Adapter, and ViewHolder .................................................................... 167
ViewHolders and Adapters .............................................................................. 168
Using a RecyclerView .................................................................................... 171
A view to display .......................................................................................... 173
Implementing a ViewHolder and an Adapter ....................................................... 173
Binding List Items ................................................................................................. 176
Responding to Presses ............................................................................................ 178
For the More Curious: ListView and GridView ........................................................... 179
For the More Curious: Singletons ............................................................................. 179
Challenge: RecyclerView ViewTypes ......................................................................... 180
9. Creating User Interfaces with Layouts and Widgets .......................................................... 181
Using the Graphical Layout Tool .............................................................................. 182
Introducing ConstraintLayout ................................................................................... 183
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Using ConstraintLayout .................................................................................. 184
The graphical editor ....................................................................................... 186
Making room ................................................................................................ 188
Adding widgets ............................................................................................. 190
ConstraintLayout’s inner workings .................................................................... 194
Editing properties ........................................................................................... 195
Making list items dynamic .............................................................................. 199
More on Layout Attributes ...................................................................................... 200
Screen pixel densities and dp and sp ................................................................. 200
Margins vs padding ........................................................................................ 202
Styles, themes, and theme attributes .................................................................. 203
Android’s design guidelines ............................................................................. 204
The Graphical Layout Tools and You ........................................................................ 204
Challenge: Formatting the Date ................................................................................ 204
10. Using Fragment Arguments ........................................................................................ 205
Starting an Activity from a Fragment ........................................................................ 205
Putting an extra ............................................................................................. 207
Retrieving an extra ......................................................................................... 207
Updating CrimeFragment’s view with Crime data ................................................ 208
The downside to direct retrieval ........................................................................ 209
Fragment Arguments .............................................................................................. 210
Attaching arguments to a fragment .................................................................... 210
Retrieving arguments ...................................................................................... 211
Reloading the List .................................................................................................. 212
Getting Results with Fragments ................................................................................ 215
For the More Curious: Why Use Fragment Arguments? ................................................ 216
Challenge: Efficient RecyclerView Reloading ............................................................. 216
Challenge: Improving CrimeLab Performance ............................................................. 216
11. Using ViewPager ...................................................................................................... 217
Creating CrimePagerActivity .................................................................................... 219
ViewPager and PagerAdapter ........................................................................... 219
Integrating CrimePagerActivity ......................................................................... 221
FragmentStatePagerAdapter vs FragmentPagerAdapter ................................................. 223
For the More Curious: How ViewPager Really Works .................................................. 224
For the More Curious: Laying Out Views in Code ....................................................... 225
Challenge: Restoring CrimeFragment’s Margins .......................................................... 226
Challenge: Adding First and Last Buttons .................................................................. 226
12. Dialogs ................................................................................................................... 227
Creating a DialogFragment ...................................................................................... 228
Showing a DialogFragment .............................................................................. 231
Setting a dialog’s contents ............................................................................... 232
Passing Data Between Two Fragments ....................................................................... 235
Passing data to DatePickerFragment .................................................................. 236
Returning data to CrimeFragment ..................................................................... 238
Challenge: More Dialogs ......................................................................................... 245
Challenge: A Responsive DialogFragment .................................................................. 245
13. The Toolbar ............................................................................................................. 247
AppCompat ........................................................................................................... 248
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Using the AppCompat library .......................................................................... 248
Menus .................................................................................................................. 250
Defining a menu in XML ................................................................................ 250
Creating the menu .......................................................................................... 256
Responding to menu selections ......................................................................... 259
Enabling Hierarchical Navigation ............................................................................. 260
How hierarchical navigation works ................................................................... 261
An Alternative Action Item ..................................................................................... 262
Toggling the action item title ........................................................................... 263
“Just one more thing...” ................................................................................... 265
For the More Curious: Action Bar vs Toolbar ............................................................. 267
Challenge: Deleting Crimes ..................................................................................... 267
Challenge: Plural String Resources ........................................................................... 268
Challenge: An Empty View for the RecyclerView ........................................................ 268
14. SQLite Databases ..................................................................................................... 269
Defining a Schema ................................................................................................. 270
Building Your Initial Database ................................................................................. 271
Exploring files using Android Device Monitor .................................................... 274
Debugging database issues .............................................................................. 276
Gutting CrimeLab .................................................................................................. 277
Writing to the Database .......................................................................................... 278
Using ContentValues ...................................................................................... 278
Inserting and updating rows ............................................................................. 279
Reading from the Database ...................................................................................... 281
Using a CursorWrapper .................................................................................. 282
Converting to model objects ............................................................................ 284
For the More Curious: More Databases ..................................................................... 287
For the More Curious: The Application Context .......................................................... 288
Challenge: Deleting Crimes ..................................................................................... 288
15. Implicit Intents ......................................................................................................... 289
Adding Buttons ..................................................................................................... 290
Adding a Suspect to the Model Layer ....................................................................... 291
Using a Format String ............................................................................................ 293
Using Implicit Intents ............................................................................................. 294
Parts of an implicit intent ................................................................................ 295
Sending a crime report .................................................................................... 296
Asking Android for a contact ........................................................................... 299
Checking for responding activities .................................................................... 302
Challenge: ShareCompat ......................................................................................... 304
Challenge: Another Implicit Intent ............................................................................ 304
16. Taking Pictures with Intents ....................................................................................... 305
A Place for Your Photo ........................................................................................... 305
File Storage .......................................................................................................... 308
Using FileProvider ......................................................................................... 309
Designating a picture location .......................................................................... 310
Using a Camera Intent ............................................................................................ 311
Firing the intent ............................................................................................. 311
Scaling and Displaying Bitmaps ............................................................................... 313
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Declaring Features ................................................................................................. 316
Challenge: Detail Display ........................................................................................ 316
Challenge: Efficient Thumbnail Load ........................................................................ 316
17. Two-Pane Master-Detail Interfaces ............................................................................... 317
Adding Layout Flexibility ....................................................................................... 319
Modifying SingleFragmentActivity ................................................................... 320
Creating a layout with two fragment containers ................................................... 321
Using an alias resource ................................................................................... 323
Creating tablet alternatives ............................................................................... 324
Activity: Fragment Boss .......................................................................................... 325
Fragment callback interfaces ............................................................................ 326
For the More Curious: More on Determining Device Size ............................................. 335
Challenge: Adding Swipe to Dismiss ........................................................................ 335
18. Localization ............................................................................................................. 337
Localizing Resources .............................................................................................. 338
Default resources ........................................................................................... 341
Checking string coverage using Translations Editor .............................................. 344
Targeting a region .......................................................................................... 345
Configuration Qualifiers .......................................................................................... 348
Prioritizing alternative resources ....................................................................... 349
Multiple qualifiers .......................................................................................... 351
Finding the best-matching resources .................................................................. 352
Testing Alternative Resources .................................................................................. 353
Challenge: Localizing Dates .................................................................................... 354
19. Accessibility ............................................................................................................ 355
TalkBack .............................................................................................................. 355
Explore by Touch .......................................................................................... 359
Linear navigation by swiping ........................................................................... 359
Making Non-Text Elements Readable by TalkBack ...................................................... 362
Adding content descriptions ............................................................................. 362
Making a widget focusable .............................................................................. 364
Creating a Comparable Experience ........................................................................... 365
Using labels to provide context ........................................................................ 367
For the More Curious: Using Accessibility Scanner ..................................................... 370
Challenge: Improving the List .................................................................................. 373
Challenge: Providing Enough Context for Data Entry ................................................... 373
Challenge: Announcing Events ................................................................................. 373
20. Data Binding and MVVM .......................................................................................... 375
Different Architectures: Why Bother? ........................................................................ 376
Creating BeatBox ................................................................................................... 376
Simple data binding ....................................................................................... 378
Importing Assets .................................................................................................... 382
Getting At Assets ................................................................................................... 384
Wiring Up Assets for Use ....................................................................................... 386
Binding to Data ..................................................................................................... 389
Creating a ViewModel .................................................................................... 391
Binding to a ViewModel ................................................................................. 392
Observable data ............................................................................................. 394
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Accessing Assets ................................................................................................... 396
For the More Curious: More About Data Binding ........................................................ 396
Lambda expressions ....................................................................................... 397
More syntactic sugar ...................................................................................... 397
BindingAdapters ............................................................................................ 397
For the More Curious: Why Assets, Not Resources ...................................................... 398
For the More Curious: Non-Assets? .......................................................................... 398
21. Unit Testing and Audio Playback ................................................................................ 399
Creating a SoundPool ............................................................................................. 399
Loading Sounds ..................................................................................................... 400
Playing Sounds ...................................................................................................... 402
Test Dependencies .................................................................................................. 402
Creating a Test Class .............................................................................................. 403
Setting Up Your Test .............................................................................................. 405
Using mocked dependencies ............................................................................ 405
Writing Tests ......................................................................................................... 407
Testing object interactions ............................................................................... 407
Data Binding Callbacks .......................................................................................... 411
Unloading Sounds .................................................................................................. 412
Rotation and Object Continuity ................................................................................ 413
Retaining a fragment ...................................................................................... 414
Rotation and retained fragments ....................................................................... 414
For the More Curious: Whether to Retain .................................................................. 416
For the More Curious: Espresso and Integration Testing ................................................ 417
For the More Curious: Mocks and Testing .................................................................. 418
Challenge: Playback Speed Control ........................................................................... 419
22. Styles and Themes .................................................................................................... 421
Color Resources .................................................................................................... 422
Styles ................................................................................................................... 422
Style inheritance ............................................................................................ 424
Themes ................................................................................................................ 425
Modifying the theme ...................................................................................... 426
Adding Theme Colors ............................................................................................ 428
Overriding Theme Attributes .................................................................................... 429
Theme spelunking .......................................................................................... 429
Modifying Button Attributes .................................................................................... 433
For the More Curious: More on Style Inheritance ........................................................ 435
For the More Curious: Accessing Theme Attributes ..................................................... 436
23. XML Drawables ....................................................................................................... 437
Making Uniform Buttons ........................................................................................ 438
Shape Drawables ................................................................................................... 439
State List Drawables ............................................................................................... 441
Layer List Drawables ............................................................................................. 443
For the More Curious: Why Bother with XML Drawables? ........................................... 444
For the More Curious: Mipmap Images ..................................................................... 445
For the More Curious: 9-Patch Images ...................................................................... 446
Challenge: Button Themes ....................................................................................... 452
24. More About Intents and Tasks .................................................................................... 453
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Setting Up NerdLauncher ........................................................................................ 454
Resolving an Implicit Intent ..................................................................................... 456
Creating Explicit Intents at Runtime .......................................................................... 460
Tasks and the Back Stack ........................................................................................ 462
Switching between tasks ................................................................................. 462
Starting a new task ......................................................................................... 464
Using NerdLauncher as a Home Screen ..................................................................... 466
Challenge: Icons .................................................................................................... 468
For the More Curious: Processes vs Tasks .................................................................. 468
For the More Curious: Concurrent Documents ............................................................ 471
25. HTTP and Background Tasks ..................................................................................... 473
Creating PhotoGallery ............................................................................................ 475
Networking Basics ................................................................................................. 477
Asking permission to network .......................................................................... 479
Using AsyncTask to Run on a Background Thread ...................................................... 479
You and Your Main Thread ..................................................................................... 481
Beyond the main thread .................................................................................. 482
Fetching JSON from Flickr ..................................................................................... 483
Parsing JSON text .......................................................................................... 487
From AsyncTask Back to the Main Thread ................................................................. 491
Cleaning Up AsyncTasks ........................................................................................ 495
For the More Curious: More on AsyncTask ................................................................ 496
For the More Curious: Alternatives to AsyncTask ........................................................ 497
Challenge: Gson .................................................................................................... 498
Challenge: Paging .................................................................................................. 498
Challenge: Dynamically Adjusting the Number of Columns .......................................... 498
26. Loopers, Handlers, and HandlerThread ......................................................................... 499
Preparing RecyclerView to Display Images ................................................................ 499
Downloading Lots of Small Things ........................................................................... 502
Communicating with the Main Thread ....................................................................... 502
Assembling a Background Thread ............................................................................ 504
Messages and Message Handlers .............................................................................. 506
Message anatomy ........................................................................................... 506
Handler anatomy ............................................................................................ 507
Using handlers .............................................................................................. 508
Passing handlers ............................................................................................ 512
For the More Curious: AsyncTasks vs Threads ............................................................ 518
For the More Curious: Solving the Image Downloading Problem .................................... 518
For the More Curious: StrictMode ............................................................................ 519
Challenge: Preloading and Caching ........................................................................... 520
27. Search .................................................................................................................... 521
Searching Flickr .................................................................................................... 521
Using SearchView .................................................................................................. 526
Responding to SearchView user interactions ....................................................... 530
Simple Persistence with Shared Preferences ................................................................ 532
Polishing Your App ................................................................................................ 536
Challenge: Polishing Your App Some More ................................................................ 536
28. Background Services ................................................................................................. 537
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Creating an IntentService ........................................................................................ 537
What Services Are For ........................................................................................... 540
Safe background networking ............................................................................ 540
Looking for New Results ........................................................................................ 542
Delayed Execution with AlarmManager ..................................................................... 544
Being a good citizen: using alarms the right way ................................................. 545
PendingIntent ................................................................................................ 547
Managing alarms with PendingIntent ................................................................. 547
Controlling Your Alarm .......................................................................................... 548
Notifications .......................................................................................................... 551
Challenge: Notifications on Android Wear .................................................................. 553
For the More Curious: Service Details ....................................................................... 553
What a service does (and does not do) ............................................................... 553
A service’s lifecycle ....................................................................................... 554
Non-sticky services ........................................................................................ 554
Sticky services ............................................................................................... 554
Bound services .............................................................................................. 555
For the More Curious: JobScheduler and JobServices ................................................... 556
JobScheduler and the future of background work ................................................. 559
Challenge: Using JobService on Lollipop ................................................................... 559
For the More Curious: Sync Adapters ....................................................................... 559
29. Broadcast Intents ...................................................................................................... 561
Regular Intents vs Broadcast Intents .......................................................................... 561
Receiving a System Broadcast: Waking Up on Boot ..................................................... 562
Creating and registering a standalone receiver ..................................................... 562
Using receivers .............................................................................................. 565
Filtering Foreground Notifications ...........................................
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Setting Up the DragAndDraw Project ........................................................................ 598
Creating a Custom View ......................................................................................... 600
Creating BoxDrawingView .............................................................................. 600
Handling Touch Events ........................................................................................... 602
Tracking across motion events .......................................................................... 604
Rendering Inside onDraw(Canvas) ............................................................................ 606
Challenge: Saving State .......................................................................................... 608
Challenge: Rotating Boxes ...................................................................................... 608
32. Property Animation ................................................................................................... 609
Building the Scene ................................................................................................. 609
Simple Property Animation ..................................................................................... 612
View transformation properties ......................................................................... 614
Using different interpolators ............................................................................ 616
Color evaluation ............................................................................................ 616
Playing Animators Together ..................................................................................... 618
For the More Curious: Other Animation APIs ............................................................. 620
Legacy animation tools ................................................................................... 620
Transitions .................................................................................................... 620
Challenges ............................................................................................................ 620
33. Locations and Play Services ....................................................................................... 621
Locations and Libraries ........................................................................................... 622
Google Play Services ...................................................................................... 622
Creating Locatr ...................................................................................................... 623
Play Services and Location Testing on Emulators ........................................................ 623
Mock location data ......................................................................................... 624
Building Out Locatr ............................................................................................... 627
Setting Up Google Play Services .............................................................................. 629
Location permissions ...................................................................................... 630
Using Google Play Services ..................................................................................... 631
Flickr Geosearch .................................................................................................... 633
Getting a Location Fix ............................................................................................ 634
Asking for Permission at Runtime ............................................................................ 637
Checking for permissions ................................................................................ 638
Find and Display an Image ...................................................................................... 644
Challenge: Permissions Rationale ............................................................................. 646
Challenge: Progress ................................................................................................ 646
34. Maps ...................................................................................................................... 647
Importing Play Services Maps .................................................................................. 647
Mapping on Android .............................................................................................. 647
Getting a Maps API Key ......................................................................................... 648
Setting Up Your Map ............................................................................................. 650
Getting More Location Data .................................................................................... 652
Working with Your Map ......................................................................................... 654
Drawing on the map ....................................................................................... 657
For the More Curious: Teams and API Keys ............................................................... 659
35. Material Design ........................................................................................................ 661
Material Surfaces ................................................................................................... 662
Elevation and Z values .................................................................................... 664
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State list animators ......................................................................................... 665
Animation Tools .................................................................................................... 667
Circular reveal ............................................................................................... 667
Shared element transitions ............................................................................... 669
View Components .................................................................................................. 673
Cards ........................................................................................................... 673
Floating action buttons .................................................................................... 675
Snackbars ..................................................................................................... 676
More on Material Design ........................................................................................ 677
36. Afterword ................................................................................................................ 679
The Final Challenge ............................................................................................... 679
Shameless Plugs .................................................................................................... 679
Thank You ............................................................................................................ 680
Index ........................................................................................................................... 681