fitsSystemWindows=true 失效问题

2024年4月15日 互联网

fitSystemWindows = "true"失效问题

          • 问题场景：
          • 问题排查：
          • 排查结果：
          • 解决方案

问题场景：

在一个沉浸式布局的Activity中存在多个设置了fitSystemWindows = "true"的控件，但是却只有一个控件生效。例如tablayout+viewpager布局中，多个子页面存在设置了fitSystemWindows = "true"的控件，但是只有第一个被找到的设置了fitSystemWindows = "true"的控件生效。

问题排查：
  1. 查看View中设置fitSystemWindows = "true"的源码，通过注释得知是通过fitSystemWindows(Rect)方法产生效果。
  /*** Sets whether or not this view should account for system screen decorations* such as the status bar and inset its content; that is, controlling whether* the default implementation of {@link #fitSystemWindows(Rect)} will be* executed.  See that method for more details.** <p>Note that if you are providing your own implementation of* {@link #fitSystemWindows(Rect)}, then there is no need to set this* flag to true -- your implementation will be overriding the default* implementation that checks this flag.** @param fitSystemWindows If true, then the default implementation of* {@link #fitSystemWindows(Rect)} will be executed.** @attr ref android.R.styleable#View_fitsSystemWindows* @see #getFitsSystemWindows()* @see #fitSystemWindows(Rect)* @see #setSystemUiVisibility(int)*/public void setFitsSystemWindows(boolean fitSystemWindows) {setFlags(fitSystemWindows ? FITS_SYSTEM_WINDOWS : 0, FITS_SYSTEM_WINDOWS);}
  1. 继续查看fitSystemWindows(Rect insets)方法，得知：
    • 处理任务被转到dispatchApplyWindowInsets(WindowInsets insets)方法中进行分发。
    • 这个方法有参数传递，通过查找被调用发现onApplyWindowInsets(WindowInsets insets)方法。
	@Deprecatedprotected boolean fitSystemWindows(Rect insets) {if ((mPrivateFlags3 & PFLAG3_APPLYING_INSETS) == 0) {if (insets == null) {// Null insets by definition have already been consumed.// This call cannot apply insets since there are none to apply,// so return false.return false;}// If we're not in the process of dispatching the newer apply insets call,// that means we're not in the compatibility path. Dispatch into the newer// apply insets path and take things from there.try {mPrivateFlags3 |= PFLAG3_FITTING_SYSTEM_WINDOWS;return dispatchApplyWindowInsets(new WindowInsets(insets)).isConsumed();} finally {mPrivateFlags3 &= ~PFLAG3_FITTING_SYSTEM_WINDOWS;}} else {// We're being called from the newer apply insets path.// Perform the standard fallback behavior.return fitSystemWindowsInt(insets);}}
  1. 继续查看onApplyWindowInsets(WindowInsets insets)方法，发现这个方式只是消耗了WindowInsets。查找方法调用发现dispatchApplyWindowInsets(WindowInsets insets)方法
public WindowInsets onApplyWindowInsets(WindowInsets insets) {if ((mPrivateFlags3 & PFLAG3_FITTING_SYSTEM_WINDOWS) == 0) {// We weren't called from within a direct call to fitSystemWindows,// call into it as a fallback in case we're in a class that overrides it// and has logic to perform.if (fitSystemWindows(insets.getSystemWindowInsets())) {return insets.consumeSystemWindowInsets();}} else {// We were called from within a direct call to fitSystemWindows.if (fitSystemWindowsInt(insets.getSystemWindowInsets())) {return insets.consumeSystemWindowInsets();}}return insets;}
  1. 查看dispatchApplyWindowInsets(WindowInsets insets)方法，得知这是个分发方法，只是将WindowInsets消耗和传递到下一级处理回调中。由问题场景可知，问题不是在下一级处理中，而是应该来自父类事件分发产生的，通过查找调用发现事件来自ViewGroup的dispatchApplyWindowInsets(WindowInsets insets)方法
public WindowInsets dispatchApplyWindowInsets(WindowInsets insets) {try {mPrivateFlags3 |= PFLAG3_APPLYING_INSETS;if (mListenerInfo != null && mListenerInfo.mOnApplyWindowInsetsListener != null) {return mListenerInfo.mOnApplyWindowInsetsListener.onApplyWindowInsets(this, insets);} else {return onApplyWindowInsets(insets);}} finally {mPrivateFlags3 &= ~PFLAG3_APPLYING_INSETS;}}
  1. 查看ViewGroup中dispatchApplyWindowInsets(WindowInsets insets)方法，发现这里分发WindowInsets时查到第一个消耗WindowInsets的子控件就返回了，WindowInsets不再继续传递给其他子控件
	@Overridepublic WindowInsets dispatchApplyWindowInsets(WindowInsets insets) {insets = super.dispatchApplyWindowInsets(insets);if (!insets.isConsumed()) {final int count = getChildCount();for (int i = 0; i < count; i++) {insets = getChildAt(i).dispatchApplyWindowInsets(insets);if (insets.isConsumed()) {break;}}}return insets;}
排查结果：

到此源码查看完毕，设置了fitSystemWindows = "true"会消耗WindowInsets事件，而 父类ViewGroup传递WindowInsets事件只给第一个消耗事件的子控件，因此导致了上述问题。

解决方案

方案一、 既然父类没有给分发WindowInsets事件，那就手动强行分发：
1. 重写父类分发；
2. 手动调用分发方法，传值当前窗口的WindowInsets（具体方案如下）
先给控件设置setFitsSystemWindows（true）/android:fitsSystemWindows=“true”

View decorView = window.getDecorView();
WindowInsets windowInsets = decorView.getRootWindowInsets();
if (windowInsets != null) {goalView.dispatchApplyWindowInsets(windowInsets.replaceSystemWindowInsets(0, windowInsets.getSystemWindowInsetTop(), 0, 0));goalView.setOnApplyWindowInsetsListener((v, insets) -> insets);
}

方案二、无需setFitsSystemWindows（true）/android:fitsSystemWindows=“true”，强行手动设置padding

View decorView = window.getDecorView();
WindowInsets windowInsets = decorView.getRootWindowInsets();
goalView.setPadding(0,windowInsets.getSystemWindowInsetTop(),0,0);
最新文章