Android 完全隐藏状态栏方法  https://blog.csdn.net/ljbphoebe/article/details/88179576

1. 隐藏ActionBar：

ActionBar actionBar = getActionBar();

if (actionBar != null) {

    actionBar.hide();

}

如果是继承AppCompatActivity，就用getSupportActionBar()。

2. 隐藏状态栏

getWindow().getDecorView().setSystemUiVisibility(View.SYSTEM_UI_FLAG_FULLSCREEN | View.SYSTEM_UI_FLAG_LAYOUT_STABLE);

通过这两个步就可以全屏显示启动页了。

然而，当开始动态申请权限，弹出系统的权限提示对话框后，状态栏又重新露出来了。我日，不是隐藏了吗？怎么又出来了，什么鬼？

通过查看源码的解释：

/**

* Request that the visibility of the status bar or other screen/window

* decorations be changed.

*

* <p>This method is used to put the over device UI into temporary modes

* where the user's attention is focused more on the application content,

* by dimming or hiding surrounding system affordances.  This is typically

* used in conjunction with {@link Window#FEATURE_ACTION_BAR_OVERLAY

* Window.FEATURE_ACTION_BAR_OVERLAY}, allowing the applications content

* to be placed behind the action bar (and with these flags other system

* affordances) so that smooth transitions between hiding and showing them

* can be done.

*

* <p>Two representative examples of the use of system UI visibility is

* implementing a content browsing application (like a magazine reader)

* and a video playing application.

*

* <p>The first code shows a typical implementation of a View in a content

* browsing application.  In this implementation, the application goes

* into a content-oriented mode by hiding the status bar and action bar,

* and putting the navigation elements into lights out mode.  The user can

* then interact with content while in this mode.  Such an application should

* provide an easy way for the user to toggle out of the mode (such as to

* check information in the status bar or access notifications).  In the

* implementation here, this is done simply by tapping on the content.

*

* {@sample development/samples/ApiDemos/src/com/example/android/apis/view/ContentBrowserActivity.java

*      content}

*

* <p>This second code sample shows a typical implementation of a View

* in a video playing application.  In this situation, while the video is

* playing the application would like to go into a complete full-screen mode,

* to use as much of the display as possible for the video.  When in this state

* the user can not interact with the application; the system intercepts

* touching on the screen to pop the UI out of full screen mode.  See

* {@link #fitSystemWindows(Rect)} for a sample layout that goes with this code.

*

* {@sample development/samples/ApiDemos/src/com/example/android/apis/view/VideoPlayerActivity.java

*      content}

*

* @param visibility  Bitwise-or of flags {@link #SYSTEM_UI_FLAG_LOW_PROFILE},

* {@link #SYSTEM_UI_FLAG_HIDE_NAVIGATION}, {@link #SYSTEM_UI_FLAG_FULLSCREEN},

* {@link #SYSTEM_UI_FLAG_LAYOUT_STABLE}, {@link #SYSTEM_UI_FLAG_LAYOUT_HIDE_NAVIGATION},

* {@link #SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN}, {@link #SYSTEM_UI_FLAG_IMMERSIVE},

* and {@link #SYSTEM_UI_FLAG_IMMERSIVE_STICKY}.

*/

从释义上可以知道，setSystemUiVisibility()是用于使系统UI进入一种临时的模式，目的是使用户的注意力关注于应用程序的内容上。所以单独一个Activity这样设置是可以全屏显示的，这个只对当前的Activity有效。可是当申请系统权限使，弹出的对话框是系统的Activity，通过adb shell dumpsys activity 来看，当前最顶端的Activity已经是GrantPermissionsActivity。

Run #2: ActivityRecord{2b99111 u0 com.google.android.packageinstaller/com.android.packageinstaller.permission.ui.GrantPermissionsActivity t141}

而这个GrantPermissionsActivity，我们并无法去设置它的setSystemUiVisibility()。所以这种方法不奏效。

通过和同事讨论，后来找到一种方法，可以实现我们的需求。

getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);

这种方法是OK的。

它的源码释义是：

/**

* Set the flags of the window, as per the

* {@link WindowManager.LayoutParams WindowManager.LayoutParams}

* flags.

*

* <p>Note that some flags must be set before the window decoration is

* created (by the first call to

* {@link #setContentView(View, android.view.ViewGroup.LayoutParams)} or

* {@link #getDecorView()}:

* {@link WindowManager.LayoutParams#FLAG_LAYOUT_IN_SCREEN} and

* {@link WindowManager.LayoutParams#FLAG_LAYOUT_INSET_DECOR}.  These

* will be set for you based on the {@link android.R.attr#windowIsFloating}

* attribute.

*

* @param flags The new window flags (see WindowManager.LayoutParams).

* @param mask Which of the window flag bits to modify.

* @see #addFlags

* @see #clearFlags

*/

public void setFlags(int flags, int mask) {}

仔细分析发现，这个是设置整个当前Window的，而setSystemUiVisibility()聚焦于显示Activity内容的，还是有差别的。

/**

* Window flag: hide all screen decorations (such as the status bar) while

* this window is displayed.  This allows the window to use the entire

* display space for itself -- the status bar will be hidden when

* an app window with this flag set is on the top layer. A fullscreen window

* will ignore a value of {@link #SOFT_INPUT_ADJUST_RESIZE} for the window's

* {@link #softInputMode} field; the window will stay fullscreen

* and will not resize.

*

* <p>This flag can be controlled in your theme through the

* {@link android.R.attr#windowFullscreen} attribute; this attribute

* is automatically set for you in the standard fullscreen themes

* such as {@link android.R.style#Theme_NoTitleBar_Fullscreen},

* {@link android.R.style#Theme_Black_NoTitleBar_Fullscreen},

* {@link android.R.style#Theme_Light_NoTitleBar_Fullscreen},

* {@link android.R.style#Theme_Holo_NoActionBar_Fullscreen},

* {@link android.R.style#Theme_Holo_Light_NoActionBar_Fullscreen},

* {@link android.R.style#Theme_DeviceDefault_NoActionBar_Fullscreen}, and

* {@link android.R.style#Theme_DeviceDefault_Light_NoActionBar_Fullscreen}.</p>

*/

public static final int FLAG_FULLSCREEN      = 0x00000400;

从释义上得知，设置这个flag可以隐藏所有的屏幕修饰，像status bar，用于Window使用整个显示屏。这个完全是我们的目的了。