DispatcherFrame强制在主窗体前插入登录窗体

当WPF的MainWindow为null时，强制登录跳转主窗体,使用队列帧强制插入

protected override Window CreateWindow()
{var login = Provider.GetService<LoginView>();var win = Provider.GetService<MainView>();bool? ok = null;// ② 手动 PushFrame，让 ShowDialog 不干扰后续 Application.Runvar frame = new DispatcherFrame();Dispatcher.BeginInvoke(DispatcherPriority.Send, new DispatcherOperationCallback(_ =>{ok = login.ShowDialog();   // 模态登录frame.Continue = false;    // 关闭登录窗后退出私有帧return null;}), null);Dispatcher.PushFrame(frame);   // 阻塞，直到登录窗关闭// ③ 登录失败直接结束进程（框架来不及 Show 任何窗）if (ok != true){ShutdownMode = ShutdownMode.OnExplicitShutdown;Shutdown(0);return null;               // 框架后续 Show(null) 会抛，但已 Shutdown，进程已退出}return win;
}