Android通过手势实现的缩放处理

主要原理是onTouchEvent事件中的参数MotionEvent，它有一个getSize()方法。在一个点的时候，该方法永远返回0,而在两个触电的时候，该方法则根据两点相对位置变化而返回不同的值。我们只需计算出两点之间的距离变化，距离的大小表明我们希望目标变化的趋势。而getX()和getY()方法则永远座落在两触点之间，这样趋势和目标我们都有了。剩下的就是对目标根据趋势进行放大或缩小即可。

public class MultiTouchTestActivity extends Activity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); // setContentView(R.layout.main); View view = new MultiTouchView(this); setContentView(view); } class MultiTouchView extends View { private float x1; private float y1; private float x2; private float y2; public MultiTouchView(Context context) { super(context); // TODO Auto-generated constructor stub } @Override public boolean onTouchEvent(MotionEvent event) { // TODO Auto-generated method stub float size = event.getSize(); int szi = (int) size; int dxi = szi >> 12; int dyit = ((1 << 12) - 1); int dyi = szi & dyit; DisplayMetrics metrics = getResources().getDisplayMetrics(); float dx = metrics.widthPixels * dxi / (float) dyit; float dy = metrics.heightPixels * dyi / (float) dyit; x1 = event.getX(); y1 = event.getY(); x2 = x1 + dx; y2 = y1 + dy; invalidate(); return true; } @Override protected void onDraw(Canvas canvas) { // TODO Auto-generated method stub super.onDraw(canvas); float r = (float) Math.sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2)) / 2; r = 50 >= r ? 50 : r; Paint paint = new Paint(); paint.setColor(Color.BLUE); canvas.drawCircle(x1, y1, r, paint); } } }