android 图片的 放大 缩小 移动

public class MainActivity extends Activity {
    
	private ImageView imageView;

    @Override
    public void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
        
            setContentView(R.layout.activity_main);
            imageView = (ImageView) findViewById(R.id.imageView);
            imageView.setOnTouchListener(new OnTouchListener() {
            // 设置开始点
            private PointF startPoint = new PointF();
            // 设置图片位置的变换矩阵
            private Matrix matrix = new Matrix();
            // 设置图片当前位置的变换矩阵
            private Matrix currentMatrix = new Matrix();
            // 初始化模式参数
            private int mode = 0;
            // 无模式
            private static final int NONE = 0;
            // 拖拉模式
            private static final int DRAG = 1;
            // 缩放模式
            private static final int ZOOM = 2;
            // 开启缩放效果的门槛
            private static final float ZOOM_THRESHOLD = 10.0f;
            // 开始距离
            private float startDistance;
            // 中心点
            private PointF middlePoint;
            
            @Override
            public boolean onTouch(View v, MotionEvent event) {
               
             	switch (event.getAction() & MotionEvent.ACTION_MASK) {
                case MotionEvent.ACTION_DOWN:
                    mode = DRAG;
                    // 记录图片当前的移动位置
                    currentMatrix.set(imageView.getImageMatrix());
                    // 记录开始坐标
                    startPoint.set(event.getX(), event.getY());
                    break;
                    
                 // 当屏幕上已经有触点（手指），再有手指按下时触发该事件
                case MotionEvent.ACTION_POINTER_DOWN:
                    mode = ZOOM;
                    //得到两点间的距离
                    startDistance = getDistance(event);
                    //如果大于
                    if(startDistance > ZOOM_THRESHOLD) {
                    	//得到两点的中间点
                        middlePoint = getMiddlePoint(event);
                        // 记录图片当前的缩放比例
                        currentMatrix.set(imageView.getImageMatrix());
                    }
                    break;

               
                case MotionEvent.ACTION_MOVE:
                    if(mode == DRAG) {
                        // 获取X轴移动距离
                        float distanceX = event.getX() - startPoint.x;
                        // 获取Y轴移动距离
                        float distanceY = event.getY() - startPoint.y;
                        // 在上次移动停止位置的基础上再进行移动
                        matrix.set(currentMatrix);
                        // 实现图片位置移动
                        matrix.postTranslate(distanceX, distanceY);
                     }else if(mode == ZOOM) {
                        // 结束距离
                        float endDistance = getDistance(event);
                        if(endDistance > ZOOM_THRESHOLD) {
                            // 缩放比例
                            float scale = endDistance / startDistance;
                            matrix.set(currentMatrix);
                            matrix.postScale(scale, scale, middlePoint.x, middlePoint.y);
                        }
                    }
                    break;
                    
                case MotionEvent.ACTION_UP:
                // 当手指离开屏幕，但屏幕上仍有其他触点（手指）时触发该事件
                case MotionEvent.ACTION_POINTER_UP:
                    mode = 0;
                    break; 
                }
                imageView.setImageMatrix(matrix);
                return true;
            }

        });
    }
    
    
	    /**
	     * 计算两点之间的距离
	     */
	    public static float getDistance(MotionEvent event) {
	        //第二个点x、y坐标减去第一个点x、y坐标
	        float disX = event.getX(1) - event.getX(0);
	        float disY = event.getY(1) - event.getY(0);
	        return FloatMath.sqrt(disX * disX + disY * disY);
	    }
	    
	    /**
	     * 计算两点之间的中间点
	     */
	    public static PointF getMiddlePoint(MotionEvent event) {
	        float midX = (event.getX(0) + event.getX(1)) /2;
	        float midY = (event.getY(0) + event.getY(1)) /2;
	        return new PointF(midX, midY);
	    }
	    
}