通过注册OnTouchListener，来实现多点触控

public class Main extends Activity implements OnTouchListener {
	// These matrices will be used to move and zoom image
	Matrix matrix = new Matrix();
	Matrix savedMatrix = new Matrix();

	// We can be in one of these 3 states
	static final int NONE = 0;
	static final int DRAG = 1;
	static final int ZOOM = 2;
	int mode = NONE;

	// Remember some things for zooming
	PointF start = new PointF();
	PointF mid = new PointF();
	float oldDist = 1f;

	@Override
	public void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.main);
		ImageView imageView = (ImageView) findViewById(R.id.imageView);
		imageView.setOnTouchListener(this);
	}

	@Override
	public boolean onTouch(View v, MotionEvent event) {
		ImageView imageView = (ImageView) v;
		switch (event.getAction() & MotionEvent.ACTION_MASK) {
		case MotionEvent.ACTION_DOWN:
			savedMatrix.set(matrix);
			start.set(event.getX(), event.getY()); // 設置初始點位置
			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;
		}
		imageView.setImageMatrix(matrix);
		return true; // indicate event was handled
	}

	/** Determine the space between the first two fingers */
	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);
	}

	/** Calculate the mid point of the first two fingers */
	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);
	}
}