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基于 Android 9 源码
0. 概述
NavigationBar 和 StatusBar 都属于 SystemBar，也叫做 decor，就是说给 App 装饰的意思。一般的 window 的布局是在 PhoneWindowManager 的 layoutWindowLw() 方法中，而 SystemBar 是在 beginLayoutLw() 方法中布局。
当前最上层的 Activity 可以修改 SystemBar 的 visibility，可以调用 View#setSystemUiVisibility() 方法，系统也有一些针对 SystemBar visibility 的策略。最终的 visibility 保存在 PhoneWindowManager 中的 mLastSystemUiFlags 变量中。
1. NavigationBar 的布局
PhoneWindowManager 实现了 WindowManagerPolicy 接口。beginLayoutLw() 中会调用 layoutNavigationBar() 方法布局 NavigationBar。
layoutNavigationBar() 方法会先调用 navigationBarPosition() 方法返回 NavigationBar 的位置，根据不同的位置布局方式不同。以布局在下边为例，会计算 NavigationBar 的 top，然后更新 mTmpNavigationFrame 和 DisplayFrames 的相关属性。其中比较重要的是更新 DisplayFrames.mDock 变量，然后用这个变量设置 mCurrent、mVoiceContent、mContent 等变量。DisplayFrames 的各个属性在「DisplayFrames 分析：Android 中都有哪些 Frame？」有说明。
// frameworks/base/services/core/java/com/android/server/policy/PhoneWindowManager.java
public class PhoneWindowManager implements WindowManagerPolicy {
private boolean layoutNavigationBar(DisplayFrames displayFrames, int uiMode, Rect dcf,
boolean navVisible, boolean navTranslucent, boolean navAllowedHidden,
boolean statusBarExpandedNotKeyguard) {
if (mNavigationBar == null) {
return false;
}
boolean transientNavBarShowing = mNavigationBarController.isTransientShowing();
// Force the navigation bar to its appropriate place and size. We need to do this directly,
// instead of relying on it to bubble up from the nav bar, because this needs to change
// atomically with screen rotations.
final int rotation = displayFrames.mRotation;
final int displayHeight = displayFrames.mDisplayHeight;
final int displayWidth = displayFrames.mDisplayWidth;
final Rect dockFrame = displayFrames.mDock;
mNavigationBarPosition = navigationBarPosition(displayWidth, displayHeight, rotation);
if (mNavigationBarPosition == NAV_BAR_BOTTOM) {
// It's a system nav bar or a portrait screen; nav bar goes on bottom.
final int top = cutoutSafeUnrestricted.bottom
- getNavigationBarHeight(rotation, uiMode);
mTmpNavigationFrame.set(0, top, displayWidth, displayFrames.mUnrestricted.bottom);
displayFrames.mStable.bottom = displayFrames.mStableFullscreen.bottom = top;
if (transientNavBarShowing) {
mNavigationBarController.setBarShowingLw(true);
} else if (navVisible) {
mNavigationBarController.setBarShowingLw(true);
dockFrame.bottom = displayFrames.mRestricted.bottom
= displayFrames.mRestrictedOverscan.bottom = top;
} else {
// We currently want to hide the navigation UI - unless we expanded the status bar.
mNavigationBarController.setBarShowingLw(statusBarExpandedNotKeyguard);
}
if (navVisible && !navTranslucent && !navAllowedHidden
&& !mNavigationBar.isAnimatingLw()
&& !mNavigationBarController.wasRecentlyTranslucent()) {
// If the opaque nav bar is currently requested to be visible and not in the process
// of animating on or off, then we can tell the app that it is covered by it.
displayFrames.mSystem.bottom = top;
}
} else if (mNavigationBarPosition == NAV_BAR_RIGHT) {
// Landscape screen; nav bar goes to the right.
...
} else if (mNavigationBarPosition == NAV_BAR_LEFT) {
// Seascape screen; nav bar goes to the left.
...
}
// Make sure the content and current rectangles are updated to account for the restrictions
// from the navigation bar.
displayFrames.mCurrent.set(dockFrame);
displayFrames.mVoiceContent.set(dockFrame);
displayFrames.mContent.set(dockFrame);
mStatusBarLayer = mNavigationBar.getSurfaceLayer();
// And compute the final frame.
mNavigationBar.computeFrameLw(mTmpNavigationFrame, mTmpNavigationFrame,
mTmpNavigationFrame, displayFrames.mDisplayCutoutSafe, mTmpNavigationFrame, dcf,
mTmpNavigationFrame, displayFrames.mDisplayCutoutSafe,
displayFrames.mDisplayCutout, false /* parentFrameWasClippedByDisplayCutout */);
mNavigationBarController.setContentFrame(mNavigationBar.getContentFrameLw());
return mNavigationBarController.checkHiddenLw();
}
}
NavigationBar 的 top 是 cutoutSafeUnrestricted.bottom 减去 NavigationBar 高度的结果。cutoutSafeUnrestricted 是安全的窗口（Android 9 针对刘海平新增的），当没有 Overscan 的时候与 mUnrestricted 相同，即 cutoutSafeUnrestricted.bottom 的值与 DisplayFrames.mDisplayHeight 值相同。计算 NavigationBar 的 top 后设置 mTmpNavigationFrame。mTmpNavigationFrame 就是 NavigationBar 的窗口区域。
之后更新 mStable 和 mFullscreen 的 bottom 值为 top。mStable 就是应用窗口的显示区域，这就是 NavigationBar 占用应用显示区域的原因。
如果 NavigationBar 可见的话更新 dockFrame、mRestricted、mRestrictedOverscan 的 bottom 值。然后用 dockFrame 去更新 mCurrent、mVoiceContent、mContent。
最后调用 computeFrameLw() 方法计算 NavigationBar 的 contentFrame 大小，然后绑定到 mNavigationBarController。
2. StatusBar 的布局
StatusBar 的布局在 PhoneWindowManager 的 beginLayoutLw() 方法中，调用 layoutStatusBar() 方法。
// frameworks/base/services/core/java/com/android/server/policy/PhoneWindowManager.java
public class PhoneWindowManager implements WindowManagerPolicy {
@Override
public void beginLayoutLw(DisplayFrames displayFrames, int uiMode) {
boolean updateSysUiVisibility |= layoutNavigationBar(displayFrames, uiMode, dcf,
navVisible, navTranslucent, navAllowedHidden, statusBarExpandedNotKeyguard);
updateSysUiVisibility |= layoutStatusBar(
displayFrames, pf, df, of, vf, dcf, sysui, isKeyguardShowing);
if (updateSysUiVisibility) {
updateSystemUiVisibilityLw();
}
}
private boolean layoutStatusBar(DisplayFrames displayFrames, Rect pf, Rect df, Rect of, Rect vf,
Rect dcf, int sysui, boolean isKeyguardShowing) {
// decide where the status bar goes ahead of time
if (mStatusBar == null) {
return false;
}
// apply any navigation bar insets
of.set(displayFrames.mUnrestricted);
df.set(displayFrames.mUnrestricted);
pf.set(displayFrames.mUnrestricted);
vf.set(displayFrames.mStable);
mStatusBarLayer = mStatusBar.getSurfaceLayer();
// Let the status bar determine its size.
mStatusBar.computeFrameLw(pf /* parentFrame */, df /* displayFrame */,
vf /* overlayFrame */, vf /* contentFrame */, vf /* visibleFrame */,
dcf /* decorFrame */, vf /* stableFrame */, vf /* outsetFrame */,
displayFrames.mDisplayCutout, false /* parentFrameWasClippedByDisplayCutout */);
// For layout, the status bar is always at the top with our fixed height.
displayFrames.mStable.top = displayFrames.mUnrestricted.top
+ mStatusBarHeightForRotation[displayFrames.mRotation];
// Make sure the status bar covers the entire cutout height
displayFrames.mStable.top = Math.max(displayFrames.mStable.top,
displayFrames.mDisplayCutoutSafe.top);
// Tell the bar controller where the collapsed status bar content is
mTmpRect.set(mStatusBar.getContentFrameLw());
mTmpRect.intersect(displayFrames.mDisplayCutoutSafe);
mTmpRect.top = mStatusBar.getContentFrameLw().top; // Ignore top display cutout inset
mTmpRect.bottom = displayFrames.mStable.top; // Use collapsed status bar size
mStatusBarController.setContentFrame(mTmpRect);
boolean statusBarTransient = (sysui & View.STATUS_BAR_TRANSIENT) != 0;
boolean statusBarTranslucent = (sysui
& (View.STATUS_BAR_TRANSLUCENT | View.STATUS_BAR_TRANSPARENT)) != 0;
if (!isKeyguardShowing) {
statusBarTranslucent &= areTranslucentBarsAllowed();
}
// If the status bar is hidden, we don't want to cause windows behind it to scroll.
if (mStatusBar.isVisibleLw() && !statusBarTransient) {
// Status bar may go away, so the screen area it occupies is available to apps but just
// covering them when the status bar is visible.
final Rect dockFrame = displayFrames.mDock;
dockFrame.top = displayFrames.mStable.top;
displayFrames.mContent.set(dockFrame);
displayFrames.mVoiceContent.set(dockFrame);
displayFrames.mCurrent.set(dockFrame);
if (DEBUG_LAYOUT) Slog.v(TAG, "Status bar: " + String.format(
"dock=%s content=%s cur=%s", dockFrame.toString(),
displayFrames.mContent.toString(), displayFrames.mCurrent.toString()));
if (!mStatusBar.isAnimatingLw() && !statusBarTranslucent
&& !mStatusBarController.wasRecentlyTranslucent()) {
// If the opaque status bar is currently requested to be visible, and not in the
// process of animating on or off, then we can tell the app that it is covered by it.
displayFrames.mSystem.top = displayFrames.mStable.top;
}
}
return mStatusBarController.checkHiddenLw();
}}
首先设定 of /* overscanFrame */、df /* displayFrame */、pf /* parentFrame */、vf /* visibleFrame */，其中 of、df、pf 设定为 displayFrames.mUnrestricted，即屏幕大小。vf 设定为 displayFrames.mStable，mStable 的大小在调用 layoutNavigationBar() 方法后变成了除去 NavigationBar 的窗口。然后调用 mStatusBar.computeFrameLw() 方法计算 StatusBar 的 mContentFrame 大小。mContentFrame 在 IME 不存在时与 mDecorFrame 相同，IME 存在时是 mDecorFrame 除去 IME 窗口的大小。
// apply any navigation bar insets
of.set(displayFrames.mUnrestricted);
df.set(displayFrames.mUnrestricted);
pf.set(displayFrames.mUnrestricted);
vf.set(displayFrames.mStable);
mStatusBarLayer = mStatusBar.getSurfaceLayer();
// Let the status bar determine its size.
mStatusBar.computeFrameLw(pf /* parentFrame */, df /* displayFrame */,
vf /* overlayFrame */, vf /* contentFrame */, vf /* visibleFrame */,
dcf /* decorFrame */, vf /* stableFrame */, vf /* outsetFrame */,
displayFrames.mDisplayCutout, false /* parentFrameWasClippedByDisplayCutout */);
下一步修改 displayFrames.mStable，即应用的窗口。因为 StatusBar 默认显示在顶部的，所以修改 mStable.top 值。
// For layout, the status bar is always at the top with our fixed height.
displayFrames.mStable.top = displayFrames.mUnrestricted.top
+ mStatusBarHeightForRotation[displayFrames.mRotation];
// Make sure the status bar covers the entire cutout height
displayFrames.mStable.top = Math.max(displayFrames.mStable.top,
displayFrames.mDisplayCutoutSafe.top);
计算 StatusBar 的可显示区域，绑定到 mStatusBarController。
// Tell the bar controller where the collapsed status bar content is
mTmpRect.set(mStatusBar.getContentFrameLw());
mTmpRect.intersect(displayFrames.mDisplayCutoutSafe);
mTmpRect.top = mStatusBar.getContentFrameLw().top; // Ignore top display cutout inset
mTmpRect.bottom = displayFrames.mStable.top; // Use collapsed status bar size
mStatusBarController.setContentFrame(mTmpRect);
判断 StatusBar 是否是短暂显示的（Transient）或是半透明的（Translucent）。其中 sysui 就是 mLastSystemUiFlags。
boolean statusBarTransient = (sysui & View.STATUS_BAR_TRANSIENT) != 0;
boolean statusBarTranslucent = (sysui
& (View.STATUS_BAR_TRANSLUCENT | View.STATUS_BAR_TRANSPARENT)) != 0;
if (!isKeyguardShowing) {
statusBarTranslucent &= areTranslucentBarsAllowed();
}
如果 StatusBar 是可见的，且不是暂时显示的，则修改 displayFrames 的 mDock、mContent、mVoiceContent、mCurrent，其实就是除去 StatusBar 的窗口大小。还有，如果 StatusBar 是不透明的，则修改 mSystem.top 值为 mStable.top 值，这时 Activity 使用 @android:style/Theme.NoTitleBar.Fullscreen 也不会隐藏 StatusBar。
// If the status bar is hidden, we don't want to cause windows behind it to scroll.
if (mStatusBar.isVisibleLw() && !statusBarTransient) {
// Status bar may go away, so the screen area it occupies is available to apps but just
// covering them when the status bar is visible.
final Rect dockFrame = displayFrames.mDock;
dockFrame.top = displayFrames.mStable.top;
displayFrames.mContent.set(dockFrame);
displayFrames.mVoiceContent.set(dockFrame);
displayFrames.mCurrent.set(dockFrame);
if (DEBUG_LAYOUT) Slog.v(TAG, "Status bar: " + String.format(
"dock=%s content=%s cur=%s", dockFrame.toString(),
displayFrames.mContent.toString(), displayFrames.mCurrent.toString()));
if (!mStatusBar.isAnimatingLw() && !statusBarTranslucent
&& !mStatusBarController.wasRecentlyTranslucent()) {
// If the opaque status bar is currently requested to be visible, and not in the
// process of animating on or off, then we can tell the app that it is covered by it.
displayFrames.mSystem.top = displayFrames.mStable.top;
}
}
