具有预览功能的图像查看器用户控件

【实例截图】

【核心代码】

using System;
using System.Collections;
using System.ComponentModel;
using System.Drawing;
using System.Data;
using System.IO;
using System.Text;
using System.Windows.Forms;

namespace ImageViewer
{

    /// <summary>
    /// A user control used to allow previewing
    /// the previous, current and next images in a 
    /// folder containing image files
    /// </summary>
    public partial class ImageViewer : UserControl
    {
        // private member variables
        private string mFolder;
        private ArrayList mImageList;
        private int mImagePosition;
        private Image mPreviousImage;
        private Image mCurrentImage;
        private Image mNextImage;


        /// <summary>
        /// Default constructor
        /// </summary>
        public ImageViewer()
        {
            InitializeComponent();
        }


        /// <summary>
        /// Load Event for User Control
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void UserControl1_Load(object sender, EventArgs e)
        {
            // do nothing on load
        }


        /// <summary>
        /// Set the image folder location.
        /// 
        /// Store all of the image file names into the
        /// Image List (mImageList) and then load the
        /// initial images
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void btnBrowse_Click(object sender, EventArgs e)
        {
            // Label the folder browser dialog
            this.folderBrowserDialog1.Description =
                "Select the image directory.";

            // disable create folder feature of folder browser
            this.folderBrowserDialog1.ShowNewFolderButton = false;

            // display the folder browser
            DialogResult result = folderBrowserDialog1.ShowDialog();
            if (result == DialogResult.OK)
            {
                // on okay, set the image folder to the
                // folder browser's selected path
                mFolder = folderBrowserDialog1.SelectedPath;
                if (!String.IsNullOrEmpty(mFolder))
                {
                    txtImageDirectory.Text = mFolder;
                }
            }
            else
            {
                // exit if the user cancels
                return;
            }

            // initialize the image arraylist
            mImageList = new ArrayList();

            // loop through the image directory
            // and find all of the image files;
            // add the found files to the image
            // list - add other image types if
            // necessary
            DirectoryInfo dir = new DirectoryInfo(mFolder);
            foreach (FileInfo f in dir.GetFiles("*.*"))
            {
                switch (f.Extension.ToUpper())
                {
                    case ".JPG":
                        mImageList.Add(f.FullName);
                        break;
                    case ".BMP":
                        mImageList.Add(f.FullName);
                        break;
                    case ".GIF":
                        mImageList.Add(f.FullName);
                        break;
                    default:
                        break;
                }
            }

            // set the starting position to 0
            // and call the set images method
            // to load the pictures
            mImagePosition = 0;
            SetImages();
        }


        /// <summary>
        /// This function is used to set the previous,
        /// current, and next images into the 
        /// correct picture boxes
        /// </summary>
        private void SetImages()
        {
            // clear any existing images
            // memory will be an issue if
            // cycling through a large
            // number of images
            mPreviousImage = null;
            mNextImage = null;
            mCurrentImage = null;

            // set the previous image
            if (mImagePosition > 0)
            {
                try
                {
                    // set delegate
                    Image.GetThumbnailImageAbort prevCallback =
                        new Image.GetThumbnailImageAbort(ThumbnailCallback);

                    // get the previous image
                    Bitmap prevBmp = 
                        new Bitmap(mImageList[mImagePosition - 1].ToString());

                    // thumbnail the image to the size
                    // of the picture box
                    mPreviousImage =
                        prevBmp.GetThumbnailImage(160, 100, 
                        prevCallback, IntPtr.Zero);

                    // set the picture box image
                    picPreviousImage.Image = mPreviousImage;

                    // clear everything out
                    prevBmp = null;
                    prevCallback = null;
                    mPreviousImage = null;
                }
                catch 
                {
                    //stall if it hangs, the user can retry
                }
            }
            else
            {
                // at the limit; clear the
                // image
                picPreviousImage.Image = null;
            }
            
            // set current image
            if (mImagePosition < mImageList.Count)
            {
                try
                {
                    // set delegate
                    Image.GetThumbnailImageAbort currentCallback =
                        new Image.GetThumbnailImageAbort(ThumbnailCallback);

                    // get the current image
                    Bitmap currentBmp = 
                        new Bitmap(mImageList[mImagePosition].ToString());

                    // thumbnail the image to the size
                    // of the picture box
                    mCurrentImage =
                        currentBmp.GetThumbnailImage(320, 200, currentCallback, IntPtr.Zero);

                    // set the picture box image
                    picCurrentImage.Image = mCurrentImage;

                    // clear everything out
                    currentBmp = null;
                    mCurrentImage = null;
                    currentCallback = null;
                }
                catch
                {
                    //stall if it hangs, the user can retry
                }
            }
            
            // set next image
            if (mImagePosition < mImageList.Count-1)
            {
                try
                {
                    // set delegate
                    Image.GetThumbnailImageAbort nextCallback =
                        new Image.GetThumbnailImageAbort(ThumbnailCallback);

                    // get the next image
                    Bitmap nextBmp = 
                        new Bitmap(mImageList[mImagePosition   1].ToString());

                    // thumbnail the image to the size
                    // of the picture box
                    mNextImage =
                        nextBmp.GetThumbnailImage(160, 100, nextCallback, IntPtr.Zero);

                    // set the picture box image
                    picNextImage.Image = mNextImage;

                    // clear everything out
                    nextBmp = null;
                    nextCallback = null;
                    mNextImage = null;
                }
                catch
                {
                    //stall if it hangs, the user can retry
                }
            }
            else
            {
                // at the limit; clear the
                // image
                picNextImage.Image = null;
            }

            // call for garbage collection
            GC.Collect();
        }

        /// <summary>
        /// Thumbnail image abort target
        /// </summary>
        /// <returns></returns>
        public bool ThumbnailCallback()
        {
            return false;
        }


        /// <summary>
        /// Set the image position and reset all of
        /// the images when the previous image
        /// button is clicked
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void btnPreviousImage_Click(object sender, EventArgs e)
        {
            if (mImagePosition >= 0 && picPreviousImage.Image != null)
            {
                mImagePosition--;
                SetImages();
            }
        }


        /// <summary>
        /// Set the image position and reset all
        /// of the images when the next image
        /// button is clicked
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void btnNextImage_Click(object sender, EventArgs e)
        {
            if (mImagePosition <= (mImageList.Count - 2))
            {
                mImagePosition  ;
                SetImages();
            }
        }


        /// <summary>
        /// Open the current image using the default
        /// program per the user's file associations
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void btnOpenImage_Click(object sender, EventArgs e)
        {
            System.Diagnostics.Process.Start(mImageList[mImagePosition].ToString());
        }


    }
}