Android学习篇章11-VelocityTracker

public class MyGameView extends View{VelocityTracker  vt=null;public MyGameView(Context context, AttributeSet attrs, int defStyle) {super(context, attrs, defStyle);}public MyGameView(Context context, AttributeSet attrs) {super(context, attrs);}public MyGameView(Context context) {super(context);}@Overridepublic boolean onTouchEvent(MotionEvent event) {    int action=event.getAction();    switch(action)    {       case MotionEvent.ACTION_DOWN:                vt=VelocityTracker.obtain();                break;       case MotionEvent.ACTION_MOVE:                break;       case MotionEvent.ACTION_UP:       case MotionEvent.ACTION_CANCEL:       case MotionEvent.ACTION_OUTSIDE:                vt.recycle();                break;    }        vt.addMovement(event);    vt.computeCurrentVelocity(1000);    float vx=vt.getXVelocity();    float vy=vt.getYVelocity();    double dgree= Math.atan(Math.abs(vx/vy))*360/(2*Math.PI);Log.i("test","vx="+vx+"   vy="+vy+" degree="+dgree);    return true;}}

public class MainActivity extends Activity {@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);MyGameView  view=(MyGameView)findViewById(R.id.mygameview);view.setLongClickable(true);}@Overridepublic boolean onCreateOptionsMenu(Menu menu) {getMenuInflater().inflate(R.menu.main, menu);return true;}}

<RelativeLayout     xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:paddingBottom="@dimen/activity_vertical_margin"    android:paddingLeft="@dimen/activity_horizontal_margin"    android:paddingRight="@dimen/activity_horizontal_margin"    android:paddingTop="@dimen/activity_vertical_margin"    tools:context=".MainActivity" >    <com.vt.MyGameView        android:id="@+id/mygameview"        android:layout_width="match_parent"        android:layout_height="match_parent"    /></RelativeLayout>