Android activity和view判断滑动

//手指按下的点为(x1, y1)手指离开屏幕的点为(x2, y2) 
 float x1 = 0; 
 float x2 = 0; 
 float y1 = 0; 
 float y2 = 0; 
 
 @Override 
 public boolean onTouchEvent(MotionEvent event) { 
 //继承了Activity的onTouchEvent方法，直接监听点击事件 
 if(event.getAction() == MotionEvent.ACTION_DOWN) { 
 //当手指按下的时候 
 x1 = event.getX(); 
 y1 = event.getY(); 
 } 
 if(event.getAction() == MotionEvent.ACTION_UP) { 
 //当手指离开的时候 
 x2 = event.getX(); 
 y2 = event.getY(); 
 if(y1 - y2 > 50) { 
 Toast.makeText(MainActivity.this, "向上滑", Toast.LENGTH_SHORT).show(); 
 } else if(y2 - y1 > 50) { 
 Toast.makeText(MainActivity.this, "向下滑", Toast.LENGTH_SHORT).show(); 
 } else if(x1 - x2 > 50) { 
 Toast.makeText(MainActivity.this, "向左滑", Toast.LENGTH_SHORT).show(); 
 } else if(x2 - x1 > 50) { 
 Toast.makeText(MainActivity.this, "向右滑", Toast.LENGTH_SHORT).show(); 
 } 
 } 
 return super.onTouchEvent(event); 
 }