【安卓筆記】VelocityTracker使用樣本

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VelocityTracker可以擷取觸屏事件的速率。 使用步驟：

1.擷取VelocityTracker執行個體：

VelocityTracker mVelocityTracker = VelocityTracker.obtain();

2.將MotionEvent事件納入到VelocityTracker中：

mVelocityTracker.addMovement(event);

3.計算瞬時速度：

mVelocityTracker.computeCurrentVelocity(units,maxVelocity);

4.擷取xy方向上的速度：

float vX = mVelocityTracker.getXVelocity(pointId);float vY = mVelocityTracker.getYVelocity(pointId);

5.回收VelocityTracker：

mVelocityTracker.clear();mVelocityTracker.recycle();

使用樣本：

package com.example.velocitytrackerdemo;import android.app.Activity;import android.os.Bundle;import android.util.Log;import android.view.MotionEvent;import android.view.VelocityTracker;import android.view.ViewConfiguration;public class MainActivity extends Activity{private static final String TAG = "MainActivity";private VelocityTracker mVelocityTracker;private int mMaxFlingVelocity;@Overrideprotected void onCreate(Bundle savedInstanceState){super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);mMaxFlingVelocity = ViewConfiguration.get(this).getScaledMaximumFlingVelocity();}/** * 擷取速度追蹤器 * @return */private VelocityTracker getVelocityTracker(){if(mVelocityTracker == null){mVelocityTracker = VelocityTracker.obtain();}return mVelocityTracker;}/** * 回收速度追蹤器 */private void recycleVelocityTracker(){if(mVelocityTracker != null){mVelocityTracker.clear();mVelocityTracker.recycle();mVelocityTracker = null;}}@Overridepublic boolean onTouchEvent(MotionEvent event){//1.擷取速度追蹤器getVelocityTracker();//2.將當前事件納入到追蹤器中mVelocityTracker.addMovement(event);int pointId = -1;switch (event.getAction()){case MotionEvent.ACTION_DOWN:Log.i(TAG,"ACTION_DOWN");pointId = event.getPointerId(0);break;case MotionEvent.ACTION_MOVE:Log.i(TAG,"ACTION_MOVE");//3.計算當前速度mVelocityTracker.computeCurrentVelocity(1000,mMaxFlingVelocity);//擷取x y方向上的速度float vX = mVelocityTracker.getXVelocity(pointId);float vY = mVelocityTracker.getYVelocity(pointId);Log.i(TAG,"vX = "+vX+",vY = "+vY);break;case MotionEvent.ACTION_UP:Log.i(TAG,"ACTION_UP");//4.回收速度追蹤器recycleVelocityTracker();break;default:break;}return super.onTouchEvent(event);}}

【安卓筆記】VelocityTracker使用樣本