android.util.AndroidRuntimeException: requestFeature() must be called before adding content 错误解决方法

Activity全屏，网上的代码如下：
protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);

    this.requestWindowFeature(Window.FEATURE_NO_TITLE);//去掉标题栏
    this.getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);//去掉信息栏

    setContentView(R.layout.activity_main);
}

但在AS中，会提示错误：
android.util.AndroidRuntimeException: requestFeature() must be called before adding content

解决如下：
protected void onCreate(Bundle savedInstanceState) {
    this.requestWindowFeature(Window.FEATURE_NO_TITLE);//去掉标题栏
    this.getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);//去掉信息栏
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
}