沉浸式状态栏的探讨

1. 常规theme

<style name="FlagTheme" parent="Theme.AppCompat.Light.NoActionBar">
    <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
    <!-- 下面这句是默认情况 -->
    <!--<item name="android:windowTranslucentStatus">false</item>-->
</style>

default.png

2. windowTranslucentStatus true

<style name="FlagTheme" parent="Theme.AppCompat.Light.NoActionBar">
    <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
    <item name="android:windowTranslucentStatus">true</item>
</style>

可以看出状态栏已经是半透明了

windowTranslucentStatus.png

3. android:statusBarColor = @android:color/transparent

<style name="FlagTheme" parent="Theme.AppCompat.Light.NoActionBar">
    <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
    <!--<item name="android:windowTranslucentStatus">true</item>-->
    <item name="android:windowTranslucentStatus">false</item>
    <item name="android:statusBarColor">@android:color/transparent</item>
</style>

在2的基础上设置状态栏为全透明，注意：这里图片和网页背景冲突，实际上状态栏变成了全白色

statusBarTransparent.png

4. 3的解决方案，windowTranslucentNavigation = true

<style name="FlagTheme" parent="Theme.AppCompat.Light.NoActionBar">
    <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
    <item name="android:windowTranslucentStatus">false</item>
    <item name="android:statusBarColor">@android:color/transparent</item>
    <item name="android:windowTranslucentNavigation">true</item>
</style>

可以看出状态栏已经变成了全透明色，不过也可以看见navigation bar变成了半透明色

excellent.png

5. 不过设置全透明的navigation bar

<style name="FlagTheme" parent="Theme.AppCompat.Light.NoActionBar">
    <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
    <item name="android:windowTranslucentStatus">false</item>
    <item name="android:statusBarColor">@android:color/transparent</item>
    <item name="android:windowTranslucentNavigation">true</item>
    <item name="android:navigationBarColor">@android:color/transparent</item>
</style>

并没有任何变化

transparentNavigation.png

6. 那尝试设置其他颜色呢？

<style name="FlagTheme" parent="Theme.AppCompat.Light.NoActionBar">
    <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
    <item name="android:windowTranslucentStatus">false</item>
    <item name="android:statusBarColor">@android:color/transparent</item>
    <item name="android:windowTranslucentNavigation">true</item>
    <item name="android:navigationBarColor">@android:color/holo_blue_bright</item>
</style>

并没有效果，猜测，设置了透明操作栏之后，并不允许再设置操作栏的颜色

blueNavigation.png

7. 那回到原点，设置状态栏颜色和操作栏颜色呢

<style name="FlagTheme" parent="Theme.AppCompat.Light.NoActionBar">
    <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
    <item name="android:statusBarColor">@android:color/holo_blue_dark</item>
    <item name="android:navigationBarColor">@android:color/holo_blue_dark</item>
</style>

colorPrimaryDark没有效果了，直接设置状态栏的颜色即可

blueAll.png

8. 全屏theme, 这个最简单

<style name="FlagTheme" parent="Theme.AppCompat.Light.NoActionBar">
    <item name="android:windowFullscreen">true</item>
</style>

但是还是有操作栏

fullscreen.png

9. 隐藏操作栏

使用theme是无法实现这个效果的，只有通过代码

Window window = getWindow();
window.getDecorView().setSystemUiVisibility(View.SYSTEM_UI_FLAG_FULLSCREEN | View.SYSTEM_UI_FLAG_HIDE_NAVIGATION);

根据google的说明，navigation非常重要，只是一个临时的flag, 只要用户有任何操作，都会被清除。

/**
 * Flag for {@link #setSystemUiVisibility(int)}: View has requested that the
 * system navigation be temporarily hidden.
 *
 * <p>This is an even less obtrusive state than that called for by
 * {@link #SYSTEM_UI_FLAG_LOW_PROFILE}; on devices that draw essential navigation controls
 * (Home, Back, and the like) on screen, <code>SYSTEM_UI_FLAG_HIDE_NAVIGATION</code> will cause
 * those to disappear. This is useful (in conjunction with the
 * {@link android.view.WindowManager.LayoutParams#FLAG_FULLSCREEN FLAG_FULLSCREEN} and
 * {@link android.view.WindowManager.LayoutParams#FLAG_LAYOUT_IN_SCREEN FLAG_LAYOUT_IN_SCREEN}
 * window flags) for displaying content using every last pixel on the display.  
 * 
 * <p>There is a limitation: because navigation controls are so important, the least user
 * interaction will cause them to reappear immediately.  When this happens, both
 * this flag and {@link #SYSTEM_UI_FLAG_FULLSCREEN} will be cleared automatically, 
 * so that both elements reappear at the same time.
 *
 * @see #setSystemUiVisibility(int) 
 */
public static final int SYSTEM_UI_FLAG_HIDE_NAVIGATION = 0x00000002;

There is a limitation: because navigation controls are so important, the least user 
interaction will cause them to reappear immediately.  When this happens, both 
this flag and {@link #SYSTEM_UI_FLAG_FULLSCREEN} will be cleared automatically, 
so that both elements reappear at the same time.

翻译：

这存在一个限制，因为操作栏的控制非常重要，所以用户的任何操作都会让它显示出来。
在这种情况下，当操作栏显示出来之后，这个flag和`SYSTEM_UI_FLAG_FULLSCREEN`将会被自动清除。
所以，所有的元素将同时出现

参考

Android9.0 完全隐藏导航栏、状态栏

Android沉浸式状态栏实现

Android 5.0 如何实现将布局的内容延伸到状态栏?