为什么开发Android无法设置全屏？

1、//在onCreat方法中setContentView（）之前插入
requestWindowFeature(Window.FEATURE_NO_TITLE);//取消标题栏
getWindow().setFlags(WindowManager.LayoutParams. FLAG_FULLSCREEN ,
WindowManager.LayoutParams. FLAG_FULLSCREEN);//全屏
注：这种方法在启动activity时会闪现状态栏之后再全屏
2、在manifest里面配置：只在当前Activity内显示全屏
为整个应用配置全屏显示
3、/**
* 全屏切换
*/
public void fullScreenChange() {
SharedPreferences mPreferences = PreferenceManager.getDefaultSharedPreferences(this);
boolean fullScreen = mPreferences.getBoolean("fullScreen", false);
WindowManager.LayoutParams attrs = getWindow().getAttributes();
System.out.println("fullScreen的值:" + fullScreen);
if (fullScreen) {
attrs.flags &= (~WindowManager.LayoutParams.FLAG_FULLSCREEN);
getWindow().setAttributes(attrs);
//取消全屏设置
getWindow().clearFlags(WindowManager.LayoutParams.FLAG_LAYOUT_NO_LIMITS);
mPreferences.edit().putBoolean("fullScreen", false).commit() ;
} else {
attrs.flags |= WindowManager.LayoutParams.FLAG_FULLSCREEN;
getWindow().setAttributes(attrs);
getWindow().addFlags(WindowManager.LayoutParams.FLAG_LAYOUT_NO_LIMITS);
mPreferences.edit().putBoolean("fullScreen", true).commit();
}
}