[Android] 状态栏的一些认识

前段时间遇到几个关于状态栏的问题，又了解了一下状态栏相关的知识，现在做一下记录。

本文地址：http://www.cnblogs.com/rossoneri/p/4316343.html 

前戏和问题

首先一般的设备都含有两个bar：顶部的状态栏(statusbar)和底部的工具栏(NavigationBar)，关于这两个Bar我最初的认识在于之前的文章：

[Android]获取系统顶部状态栏(StatusBar)与底部工具栏(NavigationBar)的高度

通过之前文章的方法就可以获取屏幕高度，来对界面进行一番设计。但后来我突然发现了一个棘手的新问题，我遇到了这么一个蛋疼的界面：

它竟然把两个Bar合并到一起了。。。我去。。

因为之前的一个控件设计是考虑了上下两条Bar的高度，然后相对顶部工具栏来进行计算，结果遇上这么个屏幕，界面的控件纵向显示就出现了小的偏移，大概30dp左右。

好了，问题来了，那就着手解决吧。

思考和解决

既然你把上下的Bar合并在一起，那么原来顶部的statusbar是隐藏了么？

我先用前文提到的方法试试输出顶部状态栏的高度，结果得到一个高度，是25。嗯，跟我看到的大概30dp高度差不多，也就是说顶部状态栏高度是存在的。那是被隐藏了么？

想知道这个，就需要找找Android是否有提供一个获取statusbar显示状态的方法。查了查API，找到了一个方法：

 int n = mActivity.getWindow().getDecorView().getSystemUiVisibility();

结果得到 n =  0 

看了看 0 的含义：

    /**
     * Special constant for {@link #setSystemUiVisibility(int)}: View has
     * requested the system UI (status bar) to be visible (the default).
     *
     * @see #setSystemUiVisibility(int)
     */
    public static final int SYSTEM_UI_FLAG_VISIBLE = 0;

也就是说顶部的statusbar是默认的可见状态。WTF，我明明看不见了，你竟然说还是默认的显示状态。好吧，难道这个statusbar移到底部合并 显示 了吗？但高度不对呀。

带着疑问，我又试着输出底部工具栏高度，得到了48。跟之前的设备一样，底部的高度没有变。

得，说到底，两条Bar的高度是都可以获取到的，而且值和正常的一样，虽然顶部的看不见，但状态还是默认的可见的，显示成这个样式是系统定制时设定的。姑且这么理解吧。

既然底部的工具栏高度没有变化，我的控件就重新以底部为参照来计算好了。用这个方法，暂且解决了控件显示位置的问题。

拓展知识

经过上面的问题，好歹是解决了眼前的bug。趁着看到这一块，我就又多了解了一下表示bar状态的几个标识：

/**
     * Special constant for {@link #setSystemUiVisibility(int)}: View has
     * requested the system UI (status bar) to be visible (the default).
     *
     * @see #setSystemUiVisibility(int)
     */
    public static final int SYSTEM_UI_FLAG_VISIBLE = 0;

    /**
     * Flag for {@link #setSystemUiVisibility(int)}: View has requested the
     * system UI to enter an unobtrusive "low profile" mode.
     *
     * <p>This is for use in games, book readers, video players, or any other
     * "immersive" application where the usual system chrome is deemed too distracting.
     *
     * <p>In low profile mode, the status bar and/or navigation icons may dim.
     *
     * @see #setSystemUiVisibility(int)
     */
    public static final int SYSTEM_UI_FLAG_LOW_PROFILE = 0x00000001;

    /**
     * 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;

    /**
     * Flag for {@link #setSystemUiVisibility(int)}: View has requested to go
     * into the normal fullscreen mode so that its content can take over the screen
     * while still allowing the user to interact with the application.
     *
     * <p>This has the same visual effect as
     * {@link android.view.WindowManager.LayoutParams#FLAG_FULLSCREEN
     * WindowManager.LayoutParams.FLAG_FULLSCREEN},
     * meaning that non-critical screen decorations (such as the status bar) will be
     * hidden while the user is in the View's window, focusing the experience on
     * that content.  Unlike the window flag, if you are using ActionBar in
     * overlay mode with {@link Window#FEATURE_ACTION_BAR_OVERLAY
     * Window.FEATURE_ACTION_BAR_OVERLAY}, then enabling this flag will also
     * hide the action bar.
     *
     * <p>This approach to going fullscreen is best used over the window flag when
     * it is a transient state -- that is, the application does this at certain
     * points in its user interaction where it wants to allow the user to focus
     * on content, but not as a continuous state.  For situations where the application
     * would like to simply stay full screen the entire time (such as a game that
     * wants to take over the screen), the
     * {@link android.view.WindowManager.LayoutParams#FLAG_FULLSCREEN window flag}
     * is usually a better approach.  The state set here will be removed by the system
     * in various situations (such as the user moving to another application) like
     * the other system UI states.
     *
     * <p>When using this flag, the application should provide some easy facility
     * for the user to go out of it.  A common example would be in an e-book
     * reader, where tapping on the screen brings back whatever screen and UI
     * decorations that had been hidden while the user was immersed in reading
     * the book.
     *
     * @see #setSystemUiVisibility(int)
     */
    public static final int SYSTEM_UI_FLAG_FULLSCREEN = 0x00000004;

    /**
     * Flag for {@link #setSystemUiVisibility(int)}: When using other layout
     * flags, we would like a stable view of the content insets given to
     * {@link #fitSystemWindows(Rect)}.  This means that the insets seen there
     * will always represent the worst case that the application can expect
     * as a continuous state.  In the stock Android UI this is the space for
     * the system bar, nav bar, and status bar, but not more transient elements
     * such as an input method.
     *
     * The stable layout your UI sees is based on the system UI modes you can
     * switch to.  That is, if you specify {@link #SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN}
     * then you will get a stable layout for changes of the
     * {@link #SYSTEM_UI_FLAG_FULLSCREEN} mode; if you specify
     * {@link #SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN} and
     * {@link #SYSTEM_UI_FLAG_LAYOUT_HIDE_NAVIGATION}, then you can transition
     * to {@link #SYSTEM_UI_FLAG_FULLSCREEN} and {@link #SYSTEM_UI_FLAG_HIDE_NAVIGATION}
     * with a stable layout.  (Note that you should avoid using
     * {@link #SYSTEM_UI_FLAG_LAYOUT_HIDE_NAVIGATION} by itself.)
     *
     * If you have set the window flag {@link WindowManager.LayoutParams#FLAG_FULLSCREEN}
     * to hide the status bar (instead of using {@link #SYSTEM_UI_FLAG_FULLSCREEN}),
     * then a hidden status bar will be considered a "stable" state for purposes
     * here.  This allows your UI to continually hide the status bar, while still
     * using the system UI flags to hide the action bar while still retaining
     * a stable layout.  Note that changing the window fullscreen flag will never
     * provide a stable layout for a clean transition.
     *
     * <p>If you are using ActionBar in
     * overlay mode with {@link Window#FEATURE_ACTION_BAR_OVERLAY
     * Window.FEATURE_ACTION_BAR_OVERLAY}, this flag will also impact the
     * insets it adds to those given to the application.
     */
    public static final int SYSTEM_UI_FLAG_LAYOUT_STABLE = 0x00000100;

    /**
     * Flag for {@link #setSystemUiVisibility(int)}: View would like its window
     * to be layed out as if it has requested
     * {@link #SYSTEM_UI_FLAG_HIDE_NAVIGATION}, even if it currently hasn't.  This
     * allows it to avoid artifacts when switching in and out of that mode, at
     * the expense that some of its user interface may be covered by screen
     * decorations when they are shown.  You can perform layout of your inner
     * UI elements to account for the navigation system UI through the
     * {@link #fitSystemWindows(Rect)} method.
     */
    public static final int SYSTEM_UI_FLAG_LAYOUT_HIDE_NAVIGATION = 0x00000200;

    /**
     * Flag for {@link #setSystemUiVisibility(int)}: View would like its window
     * to be layed out as if it has requested
     * {@link #SYSTEM_UI_FLAG_FULLSCREEN}, even if it currently hasn't.  This
     * allows it to avoid artifacts when switching in and out of that mode, at
     * the expense that some of its user interface may be covered by screen
     * decorations when they are shown.  You can perform layout of your inner
     * UI elements to account for non-fullscreen system UI through the
     * {@link #fitSystemWindows(Rect)} method.
     */
    public static final int SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN = 0x00000400;

    /**
     * Flag for {@link #setSystemUiVisibility(int)}: View would like to remain interactive when
     * hiding the navigation bar with {@link #SYSTEM_UI_FLAG_HIDE_NAVIGATION}.  If this flag is
     * not set, {@link #SYSTEM_UI_FLAG_HIDE_NAVIGATION} will be force cleared by the system on any
     * user interaction.
     * <p>Since this flag is a modifier for {@link #SYSTEM_UI_FLAG_HIDE_NAVIGATION}, it only
     * has an effect when used in combination with that flag.</p>
     */
    public static final int SYSTEM_UI_FLAG_IMMERSIVE = 0x00000800;

    /**
     * Flag for {@link #setSystemUiVisibility(int)}: View would like to remain interactive when
     * hiding the status bar with {@link #SYSTEM_UI_FLAG_FULLSCREEN} and/or hiding the navigation
     * bar with {@link #SYSTEM_UI_FLAG_HIDE_NAVIGATION}.  Use this flag to create an immersive
     * experience while also hiding the system bars.  If this flag is not set,
     * {@link #SYSTEM_UI_FLAG_HIDE_NAVIGATION} will be force cleared by the system on any user
     * interaction, and {@link #SYSTEM_UI_FLAG_FULLSCREEN} will be force-cleared by the system
     * if the user swipes from the top of the screen.
     * <p>When system bars are hidden in immersive mode, they can be revealed temporarily with
     * system gestures, such as swiping from the top of the screen.  These transient system bars
     * will overlay app’s content, may have some degree of transparency, and will automatically
     * hide after a short timeout.
     * </p><p>Since this flag is a modifier for {@link #SYSTEM_UI_FLAG_FULLSCREEN} and
     * {@link #SYSTEM_UI_FLAG_HIDE_NAVIGATION}, it only has an effect when used in combination
     * with one or both of those flags.</p>
     */
    public static final int SYSTEM_UI_FLAG_IMMERSIVE_STICKY = 0x00001000;

    /**
     * @deprecated Use {@link #SYSTEM_UI_FLAG_LOW_PROFILE} instead.
     */
    public static final int STATUS_BAR_HIDDEN = SYSTEM_UI_FLAG_LOW_PROFILE;

    /**
     * @deprecated Use {@link #SYSTEM_UI_FLAG_VISIBLE} instead.
     */
    public static final int STATUS_BAR_VISIBLE = SYSTEM_UI_FLAG_VISIBLE;

    /**
     * @hide
     *
     * NOTE: This flag may only be used in subtreeSystemUiVisibility. It is masked
     * out of the public fields to keep the undefined bits out of the developer's way.
     *
     * Flag to make the status bar not expandable.  Unless you also
     * set {@link #STATUS_BAR_DISABLE_NOTIFICATION_ICONS}, new notifications will continue to show.
     */
    public static final int STATUS_BAR_DISABLE_EXPAND = 0x00010000;

    /**
     * @hide
     *
     * NOTE: This flag may only be used in subtreeSystemUiVisibility. It is masked
     * out of the public fields to keep the undefined bits out of the developer's way.
     *
     * Flag to hide notification icons and scrolling ticker text.
     */
    public static final int STATUS_BAR_DISABLE_NOTIFICATION_ICONS = 0x00020000;

    /**
     * @hide
     *
     * NOTE: This flag may only be used in subtreeSystemUiVisibility. It is masked
     * out of the public fields to keep the undefined bits out of the developer's way.
     *
     * Flag to disable incoming notification alerts.  This will not block
     * icons, but it will block sound, vibrating and other visual or aural notifications.
     */
    public static final int STATUS_BAR_DISABLE_NOTIFICATION_ALERTS = 0x00040000;

    /**
     * @hide
     *
     * NOTE: This flag may only be used in subtreeSystemUiVisibility. It is masked
     * out of the public fields to keep the undefined bits out of the developer's way.
     *
     * Flag to hide only the scrolling ticker.  Note that
     * {@link #STATUS_BAR_DISABLE_NOTIFICATION_ICONS} implies
     * {@link #STATUS_BAR_DISABLE_NOTIFICATION_TICKER}.
     */
    public static final int STATUS_BAR_DISABLE_NOTIFICATION_TICKER = 0x00080000;

    /**
     * @hide
     *
     * NOTE: This flag may only be used in subtreeSystemUiVisibility. It is masked
     * out of the public fields to keep the undefined bits out of the developer's way.
     *
     * Flag to hide the center system info area.
     */
    public static final int STATUS_BAR_DISABLE_SYSTEM_INFO = 0x00100000;

    /**
     * @hide
     *
     * NOTE: This flag may only be used in subtreeSystemUiVisibility. It is masked
     * out of the public fields to keep the undefined bits out of the developer's way.
     *
     * Flag to hide only the home button.  Don't use this
     * unless you're a special part of the system UI (i.e., setup wizard, keyguard).
     */
    public static final int STATUS_BAR_DISABLE_HOME = 0x00200000;

    /**
     * @hide
     *
     * NOTE: This flag may only be used in subtreeSystemUiVisibility. It is masked
     * out of the public fields to keep the undefined bits out of the developer's way.
     *
     * Flag to hide only the back button. Don't use this
     * unless you're a special part of the system UI (i.e., setup wizard, keyguard).
     */
    public static final int STATUS_BAR_DISABLE_BACK = 0x00400000;

    /**
     * @hide
     *
     * NOTE: This flag may only be used in subtreeSystemUiVisibility. It is masked
     * out of the public fields to keep the undefined bits out of the developer's way.
     *
     * Flag to hide only the clock.  You might use this if your activity has
     * its own clock making the status bar's clock redundant.
     */
    public static final int STATUS_BAR_DISABLE_CLOCK = 0x00800000;

    /**
     * @hide
     *
     * NOTE: This flag may only be used in subtreeSystemUiVisibility. It is masked
     * out of the public fields to keep the undefined bits out of the developer's way.
     *
     * Flag to hide only the recent apps button. Don't use this
     * unless you're a special part of the system UI (i.e., setup wizard, keyguard).
     */
    public static final int STATUS_BAR_DISABLE_RECENT = 0x01000000;

    /**
     * @hide
     *
     * NOTE: This flag may only be used in subtreeSystemUiVisibility. It is masked
     * out of the public fields to keep the undefined bits out of the developer's way.
     *
     * Flag to disable the global search gesture. Don't use this
     * unless you're a special part of the system UI (i.e., setup wizard, keyguard).
     */
    public static final int STATUS_BAR_DISABLE_SEARCH = 0x02000000;

    /**
     * @hide
     *
     * NOTE: This flag may only be used in subtreeSystemUiVisibility. It is masked
     * out of the public fields to keep the undefined bits out of the developer's way.
     *
     * Flag to specify that the status bar is displayed in transient mode.
     */
    public static final int STATUS_BAR_TRANSIENT = 0x04000000;

    /**
     * @hide
     *
     * NOTE: This flag may only be used in subtreeSystemUiVisibility. It is masked
     * out of the public fields to keep the undefined bits out of the developer's way.
     *
     * Flag to specify that the navigation bar is displayed in transient mode.
     */
    public static final int NAVIGATION_BAR_TRANSIENT = 0x08000000;

    /**
     * @hide
     *
     * NOTE: This flag may only be used in subtreeSystemUiVisibility. It is masked
     * out of the public fields to keep the undefined bits out of the developer's way.
     *
     * Flag to specify that the hidden status bar would like to be shown.
     */
    public static final int STATUS_BAR_UNHIDE = 0x10000000;

    /**
     * @hide
     *
     * NOTE: This flag may only be used in subtreeSystemUiVisibility. It is masked
     * out of the public fields to keep the undefined bits out of the developer's way.
     *
     * Flag to specify that the hidden navigation bar would like to be shown.
     */
    public static final int NAVIGATION_BAR_UNHIDE = 0x20000000;

    /**
     * @hide
     *
     * NOTE: This flag may only be used in subtreeSystemUiVisibility. It is masked
     * out of the public fields to keep the undefined bits out of the developer's way.
     *
     * Flag to specify that the status bar is displayed in translucent mode.
     */
    public static final int STATUS_BAR_TRANSLUCENT = 0x40000000;

    /**
     * @hide
     *
     * NOTE: This flag may only be used in subtreeSystemUiVisibility. It is masked
     * out of the public fields to keep the undefined bits out of the developer's way.
     *
     * Flag to specify that the navigation bar is displayed in translucent mode.
     */
    public static final int NAVIGATION_BAR_TRANSLUCENT = 0x80000000;

    /**
     * @hide
     */
    public static final int PUBLIC_STATUS_BAR_VISIBILITY_MASK = 0x0000FFFF;

关于几个常用的我挨个试验了一下

getWindow().getDecorView().setSystemUiVisibility(标识)

然后操作了一下程序，得到下面的初步结论：

SYSTEM_UI_FLAG_FULLSCREEN	bar存在，内容消失 显示一个点
SYSTEM_UI_FLAG_HIDE_NAVIGATION	navigation_bar消失
SYSTEM_UI_FLAG_FULLSCREEN	status_bar消失
SYSTEM_UI_FLAG_LAYOUT_STABLE	不变
SYSTEM_UI_FLAG_LAYOUT_HIDE_NAVIGATION	上下bar还在，但显示的内容拓展到被bar盖住的区域了好像
SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN	上下bar还在，显示的内容拓展到上面bar的位置
SYSTEM_UI_FLAG_IMMERSIVE	不变
SYSTEM_UI_FLAG_IMMERSIVE_STICKY	不变

可以结合着源码里的官方注释来看看
 

一个新问题

 看完这，我突然想起来之前遇到的另一个问题：

我写了一个popupwindow，希望它在靠上的位置弹出来时这么显示

 结果它是这么显示的：

哎我去，当时我真是百思不得其解，因为各种高度我都考虑到，写到计算代码里，意思是一旦遇到顶部显示的情况，popupwindow就自动向下偏移一个距离完整显示。

另外，popupwindow作为一个弹出时单独在最上层显示的控件，就算我不控制它，它也不应该显示一半吧。

后来我实在没办法就强行在代码里增加了35左右的高度好让它完整显示。

现在看来，原来是界面显示的时候，顶部边界并不是状态栏的bottom，而是整个屏幕的顶部。出现这个情况是因为statusbar盖住了上面的一部分而已，只是我不知道罢了。。

好了，下次设计界面的时候我会注意把statusbar的高度减掉的。。。

以上就是我对Android状态栏的一点新理解。若不正确，但求拍砖。

参考：

动态显示和隐藏状态栏