Alert Dialog弹窗无法显示，报错Unable to add window android.view.ViewRootImpl$W. permission denied

　Android 11上点击事件触发AlertDialog弹窗时，弹窗无法显示；后台打印提示Unable to add window android.view.ViewRootImpl$W. permission denied

代码中设置窗口类型时使用的TYPE_SYSTEM_ALERT，

dialog.getWindow().setType(WindowManager.LayoutParams.TYPE_SYSTEM_ALERT);

　　关于TYPE_SYSTEM_ALERT在源码中的解释

        /**
         * Window type: system window, such as low power alert. These windows
         * are always on top of application windows.
         * In multiuser systems shows only on the owning user's window.
         * @deprecated for non-system apps. Use {@link #TYPE_APPLICATION_OVERLAY} instead.
         */
        @Deprecated
        public static final int TYPE_SYSTEM_ALERT       = FIRST_SYSTEM_WINDOW+3;

　　该类型为系统级别窗口，用于低电量提示等信息显示，窗口显示在最顶部。对于非系统的app，应该使用TYPE_APPLICATION_OVERLAY替代。但是设置这个类型的情况下，可能会被系统弹窗覆盖掉，因此我们需要将它设置为既能显示在最顶部，也不会被其他系统弹窗覆盖的类型。

　　我们可以使用TYPE_SYSTEM_OVERYLAY类型，同时也不会报错，可以在系统上正常显示弹窗。

/**
         * Window type: system overlay windows, which need to be displayed
         * on top of everything else.  These windows must not take input
         * focus, or they will interfere with the keyguard.
         * In multiuser systems shows only on the owning user's window.
         * @deprecated for non-system apps. Use {@link #TYPE_APPLICATION_OVERLAY} instead.
         */
        @Deprecated
        public static final int TYPE_SYSTEM_OVERLAY     = FIRST_SYSTEM_WINDOW+6;

标签：ViewRootImpl,permission,OVERLAY,SYSTEM,system,window,报错,TYPE,弹窗
来源： https://www.cnblogs.com/zoowei/p/16306335.html