android 图片放大缩小，简洁 附完整源码

package com.wf.test.activity;

import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Matrix;
import android.graphics.PointF;
import android.graphics.RectF;
import android.os.Bundle;
import android.util.DisplayMetrics;
import android.util.FloatMath;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnTouchListener;
import android.widget.ImageView;

/**
 * 图片浏览、缩放、拖动、自动居中
 */
public class ImageZoomActivity extends Activity implements OnTouchListener {

    Matrix matrix = new Matrix();
    Matrix savedMatrix = new Matrix();
    DisplayMetrics dm;
    ImageView imgView;
    Bitmap bitmap;

    float minScaleR;// 最小缩放比例
    static final float MAX_SCALE = 4f;// 最大缩放比例

    static final int NONE = 0;// 初始状态
    static final int DRAG = 1;// 拖动
    static final int ZOOM = 2;// 缩放
    int mode = NONE;

    PointF prev = new PointF();
    PointF mid = new PointF();
    float dist = 1f;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        
        setContentView(R.layout.main);
        imgView = (ImageView) findViewById(R.id.image);// 获取控件
        bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.image_test);// 获取图片资源
        imgView.setImageBitmap(bitmap);// 填充控件
        imgView.setOnTouchListener(this);// 设置触屏监听
        dm = new DisplayMetrics();
        getWindowManager().getDefaultDisplay().getMetrics(dm);// 获取分辨率
        minZoom();
        center();
        imgView.setImageMatrix(matrix);
    }

    /**
     * 触屏监听
     */
    public boolean onTouch(View v, MotionEvent event) {

        switch (event.getAction() & MotionEvent.ACTION_MASK) {
        // 主点按下
        case MotionEvent.ACTION_DOWN:
            savedMatrix.set(matrix);
            prev.set(event.getX(), event.getY());
            mode = DRAG;
            break;
        // 副点按下
        case MotionEvent.ACTION_POINTER_DOWN:
            dist = spacing(event);
            // 如果连续两点距离大于10，则判定为多点模式
            if (spacing(event) > 10f) {
                savedMatrix.set(matrix);
                midPoint(mid, event);
                mode = ZOOM;
            }
            break;
        case MotionEvent.ACTION_UP:
        case MotionEvent.ACTION_POINTER_UP:
            mode = NONE;
            break;
        case MotionEvent.ACTION_MOVE:
            if (mode == DRAG) {
                matrix.set(savedMatrix);
                matrix.postTranslate(event.getX() - prev.x, event.getY()
                        - prev.y);
            } else if (mode == ZOOM) {
                float newDist = spacing(event);
                if (newDist > 10f) {
                    matrix.set(savedMatrix);
                    float tScale = newDist / dist;
                    matrix.postScale(tScale, tScale, mid.x, mid.y);
                }
            }
            break;
        }
        imgView.setImageMatrix(matrix);
        CheckView();
        return true;
    }

    /**
     * 限制最大最小缩放比例，自动居中
     */
    private void CheckView() {
        float p[] = new float[9];
        matrix.getValues(p);
        if (mode == ZOOM) {
            if (p[0] < minScaleR) {
                matrix.setScale(minScaleR, minScaleR);
            }
            if (p[0] > MAX_SCALE) {
                matrix.set(savedMatrix);
            }
        }
        center();
    }

    /**
     * 最小缩放比例，最大为100%
     */
    private void minZoom() {
        minScaleR = Math.min(
                (float) dm.widthPixels / (float) bitmap.getWidth(),
                (float) dm.heightPixels / (float) bitmap.getHeight());
        if (minScaleR < 1.0) {
            matrix.postScale(minScaleR, minScaleR);
        }
    }

    private void center() {
        center(true, true);
    }

    /**
     * 横向、纵向居中
     */
    protected void center(boolean horizontal, boolean vertical) {

        Matrix m = new Matrix();
        m.set(matrix);
        RectF rect = new RectF(0, 0, bitmap.getWidth(), bitmap.getHeight());
        m.mapRect(rect);

        float height = rect.height();
        float width = rect.width();

        float deltaX = 0, deltaY = 0;

        if (vertical) {
            // 图片小于屏幕大小，则居中显示。大于屏幕，上方留空则往上移，下方留空则往下移
            int screenHeight = dm.heightPixels;
            if (height < screenHeight) {
                deltaY = (screenHeight - height) / 2 - rect.top;
            } else if (rect.top > 0) {
                deltaY = -rect.top;
            } else if (rect.bottom < screenHeight) {
                deltaY = imgView.getHeight() - rect.bottom;
            }
        }

        if (horizontal) {
            int screenWidth = dm.widthPixels;
            if (width < screenWidth) {
                deltaX = (screenWidth - width) / 2 - rect.left;
            } else if (rect.left > 0) {
                deltaX = -rect.left;
            } else if (rect.right < screenWidth) {
                deltaX = screenWidth - rect.right;
            }
        }
        matrix.postTranslate(deltaX, deltaY);
    }

    /**
     * 两点的距离
     */
    private float spacing(MotionEvent event) {
        float x = event.getX(0) - event.getX(1);
        float y = event.getY(0) - event.getY(1);
        return FloatMath.sqrt(x * x   y * y);
    }

    /**
     * 两点的中点
     */
    private void midPoint(PointF point, MotionEvent event) {
        float x = event.getX(0)   event.getX(1);
        float y = event.getY(0)   event.getY(1);
        point.set(x / 2, y / 2);
    }
}