Android手势缩放图片以及图片黏贴在手指随手势移动

一个Android手势缩放图片的工具类；同时，此类还实现另外一个功能：当手指按在触屏上移动时候，图片“黏贴”在手指上随手指移动而整体移动。

具体使用方法可以是这样：先new一个此类的实例，然后在ImageView的方法setOnTouchListener(new ImageViewOnMultiTouchListener());

例如：

ImageViewOnMultiTouchListener listener=new ImageViewOnMultiTouchListener();
		ImageView mImageView=(ImageView)findViewById(R.id.imageView);
		mImageView.setOnTouchListener(listener);

ImageViewOnMultiTouchListener.java全部源代码：

public class ImageViewOnMultiTouchListener implements View.OnTouchListener {

		private final int NONE = 0;
		private final int MOVE = 1;
		private final int ZOOM = 2;
		private final int DRAG = 3;

		private int mode = NONE;
		private Matrix matrix = new Matrix();
		private Matrix savedMatrix = new Matrix();
		private PointF start = new PointF();
		private PointF mid = new PointF();
		private float oldDistance = 0;

		@Override
		public boolean onTouch(View v, MotionEvent event) {

			ImageView view = (ImageView) v;

			switch (event.getAction() & MotionEvent.ACTION_MASK) {
			case MotionEvent.ACTION_DOWN:
				matrix.set(view.getImageMatrix());
				savedMatrix.set(matrix);
				start.set(event.getX(), event.getY());

				mode = DRAG;

				break;

			case MotionEvent.ACTION_POINTER_DOWN:
				oldDistance = spacing(event);
				if (oldDistance > 5f) {
					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() - start.x, event.getY()
							- start.y);
				} else if (mode == ZOOM) {
					float newDist = spacing(event);
					if (newDist > 5f) {
						matrix.set(savedMatrix);
						float scale = newDist / oldDistance;
						matrix.postScale(scale, scale, mid.x, mid.y);
					}
				}

				break;
			}

			view.setImageMatrix(matrix);
			view.setScaleType(ImageView.ScaleType.MATRIX);
			view.setPadding(3, 5, 3, 5);

			return true;
		}

		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);
		}

		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);
		}
	}