Android禁止屏幕休眠

<uses-permission android:name="android.permission.WAKE_LOCK" />

public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    //要写在setContentView之前？
    getWindow().setFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON,  WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);
    setContentView(R.layout.main);
}