VelocityTracker的用法

package com.example.velocitytrackertest;

import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
import android.view.MotionEvent;
import android.view.VelocityTracker;

public class MainActivity extends Activity {
	private VelocityTracker velocityTracker;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.main);
	}

	@Override
	public boolean onTouchEvent(MotionEvent event) {
		//必须放这里，放在ACTION_DOWN里面XY输出为0
		if(velocityTracker == null){
			velocityTracker = VelocityTracker.obtain();//必须和recycle()配对
		}
		velocityTracker.addMovement(event);
		
		switch (event.getAction()) {
		case MotionEvent.ACTION_DOWN:
			break;
		case MotionEvent.ACTION_MOVE:
			velocityTracker.computeCurrentVelocity(1000);
			int X = (int)velocityTracker.getXVelocity();
			int Y = (int)velocityTracker.getYVelocity();
			Log.i("X", X + "");
			Log.i("Y", Y + "");
			break;
		case MotionEvent.ACTION_UP:
			if(velocityTracker != null){
				velocityTracker.recycle();
				velocityTracker = null;
			}
			break;
		}
		return super.onTouchEvent(event);
	}
}