图片的放大,缩小,多点触控

//使用
imageView.setScaleType(ImageView.ScaleType.MATRIX);
imageView.setOnTouchListener(new MulitPointTouchListener());

//-----------------类-------------------------

/**
 * 多点触控,图片的放大缩小
 * @date 2012-11-6
 */
public class MulitPointTouchListener implements OnTouchListener {
	Matrix matrix = new Matrix();
	Matrix savedMatrix = new Matrix();

	static final int NONE = 0;
	static final int DRAG = 1;
	static final int ZOOM = 2;
	int mode = NONE;

	PointF start = new PointF();
	PointF mid = new PointF();
	float oldDist = 1f;

	@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:
			oldDist = spacing(event);
			if (oldDist > 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() - start.x, event.getY()
						- start.y);
			} else if (mode == ZOOM) {
				float newDist = spacing(event);
				if (newDist > 10f) {
					matrix.set(savedMatrix);
					float scale = newDist / oldDist;
					matrix.postScale(scale, scale, mid.x, mid.y);
				}
			}
			break;
		}

		view.setImageMatrix(matrix);
		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);
	}
}