onWindowFocusChanged-屏幕焦点函数回调情况

1.这个函数的具体作用不太清楚,但网上有人说是 ，当activity得到或者失去焦点的时候，就会调用这个方法

先看如下代码

 @Override
    public void onWindowFocusChanged(boolean hasFocus) {
        android.util.Log.e("zhangshuli", "win");
        mHistoryDisplayButton.getLocationOnScreen(mHistoryDisplayButtonLocation);
        mHistoryDisplayButtonLocationX = mHistoryDisplayButtonLocation[0];
        mHistoryDisplayButtonLocationY = mHistoryDisplayButtonLocation[1];
        mHistoryHideButton.getLocationOnScreen(mHistoryHideButtonLocation);
        mHistoryHideButtonLocationX = mHistoryHideButtonLocation[0];
        mHistoryHideButtonLocationY = mHistoryHideButtonLocation[1];
        mHistoryDisplayListWidth = mHistoryDisplayList.getWidth();
        mHistoryHideLastLocationX =  mHistoryHideButtonLocationX - mHistoryDisplayListWidth ;
        mRotationAngle = (135f)/((float)mHistoryDisplayButtonLocationX -(float)mHistoryHideLastLocationX);
        android.util.Log.e("zhangshuli", "angle"+mRotationAngle);
        android.util.Log.e("zhangshuli", "mHistoryDisplayListWidth"+mHistoryDisplayListWidth);
        android.util.Log.e("zhangshuli", "mHistoryHideLastLocationX"+mHistoryHideLastLocationX);
        android.util.Log.e("zhangshuli", "mHistoryHideButtonLocationX"+mHistoryHideButtonLocationX);
        android.util.Log.e("zhangshuli", "mHistoryDisplayButtonLocationX"+mHistoryDisplayButtonLocationX);

        super.onWindowFocusChanged(hasFocus);
}

当我进入和退出这个activity的时候，我们可以看到打印的log如下

1）进入

- ::30.801 E/zhangshuli( ): nihao
- ::31.241 E/zhangshuli( ): win
- ::31.241 E/zhangshuli( ): angle0.
- ::31.241 E/zhangshuli( ): mHistoryDisplayListWidth362
- ::31.241 E/zhangshuli( ): mHistoryHideLastLocationX378
- ::31.241 E/zhangshuli( ): mHistoryHideButtonLocationX740
- ::31.241 E/zhangshuli( ): mHistoryDisplayButtonLocationX616

2)退出

- ::35.736 E/zhangshuli( ): win
- ::35.736 E/zhangshuli( ): angle0.
- ::35.736 E/zhangshuli( ): mHistoryDisplayListWidth362
- ::35.736 E/zhangshuli( ): mHistoryHideLastLocationX378
- ::35.736 E/zhangshuli( ): mHistoryHideButtonLocationX740
- ::35.736 E/zhangshuli( ): mHistoryDisplayButtonLocationX616

所以我们知道，这个方法是在activity加载或者退出的时候都会调用。对它唯一的认识就是，如果你想要得到一个控件的位置坐标，那么你必须在这个方法中执行相应的代码，在oncreate中是得不到的

我们现在再把它跟Oncreate做一下比较

log打印如下

 @Override
    public void onCreate(Bundle state) {
        super.onCreate(state);

        android.util.Log.e("zhangshuli", "nihao");
}

 @Override
    public void onWindowFocusChanged(boolean hasFocus) {
        android.util.Log.e("zhangshuli", "win");

        super.onWindowFocusChanged(hasFocus);
}

1)当我们启动应用的时候

- ::37.577 E/zhangshuli( ): nihao
- ::38.178 E/zhangshuli( ): win

2)按下HOME建

- ::19.584 E/zhangshuli( ): win

3)按下HOME建再次进入

- ::25.664 E/zhangshuli( ): win

4)直接退出

- ::30.899 E/zhangshuli( ): win

可以得到一个结论，就是oncreate比focus先执行。但是，如论程序怎么走，都会执行focus