android VelocityTracker和 GestureDetector滑动监听工具类

这次将两个滑动监听工具类，是方便我们判断当前滑动状态的。

VelocityTracker：速度监听，能够监听x轴和y轴上的分量速度。

GestureDetector：能够检测用户的单击，滑动，双击等行为。

使用例子如下：

public class MainActivity extends AppCompatActivity {

private MyView view;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
view = new MyView(this);
setContentView(view);
}
}

public class MyView extends View implements GestureDetector.OnGestureListener {

private int x,y,left,right,top,bottom,rawX,rawY,touchslop;
private int startx=0,starty=0,endx=0,endy=0;
private String state="";
private GestureDetector mGestureDetector ;
public MyView(Context context) {
super(context);
setFocusable(true);
touchslop= ViewConfiguration.get(context).getScaledTouchSlop();
mGestureDetector = new GestureDetector(this);
//解决长按后屏幕无法拖动，但是却无法判断长按的情况
mGestureDetector.setIsLongpressEnabled(false);
}

@Override protected void onDraw(Canvas canvas) {

Paint paint = new Paint();
paint.setColor(Color.BLACK);
paint.setTextSize(40);
canvas.drawText(" x:" + x + " y:" + y, 50, 100, paint);

super.onDraw(canvas);
}

@Override public boolean onKeyDown(int keyCode,KeyEvent event) {
return super.onKeyDown(keyCode, event);
}

@Override public boolean onKeyUp(int keyCode,KeyEvent event) {
return super.onKeyUp(keyCode, event);
}

@Override public boolean onTouchEvent(MotionEvent event) {

VelocityTracker velocityTracker = VelocityTracker.obtain();
velocityTracker.addMovement(event);
velocityTracker.computeCurrentVelocity(1000);
x=(int)velocityTracker.getXVelocity();
y=(int)velocityTracker.getYVelocity();

invalidate();
velocityTracker.clear();
velocityTracker.recycle();

mGestureDetector.onTouchEvent(event);
return true;
}

@Override
public boolean onDown(MotionEvent e) {
Log.v("zzw","onDown");
return false;
}

@Override
public void onShowPress(MotionEvent e) {
Log.v("zzw","onShowPress");
}

@Override
public boolean onSingleTapUp(MotionEvent e) {
Log.v("zzw","onSingleTapUp");
return false;
}

@Override
public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY) {
Log.v("zzw","onScroll");
return false;
}

@Override
public void onLongPress(MotionEvent e) {
Log.v("zzw","onLongPress");
}

@Override
public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {
Log.v("zzw","onFling");
return false;
}

}

使用方法都很简单，mGestureDetector.setIsLongpressEnabled(false)这个命令慎用，因为它会导致GestureDetector无法判断长按状态。

还有就是 velocityTracker.clear();

velocityTracker.recycle();，记得用完VelocityTracker，要进行回收资源。

再见