• 创建单个窗口
• 将其Content和DataContext设置为“启动屏幕”
• 在显示闪屏时执行初始化操作
• 初始化代码完成后，用主内容和视图模型替换窗口的Content和DataContext

大概是这样的

protected override async void OnLaunched(Microsoft.UI.Xaml.LaunchActivatedEventArgs args)
{

    Window m_window = new NavigationRootWindow();
    m_window.Content = new TextBlock() { Text = "Loading..." };
    m_window.Activate();

    //TODO: login the user...
    await Task.Delay(5000);

    m_window.Content = new TextBlock() { Text = "Welcome!" };
}

我修改/扩展了用户mm 8的解决方案。

• 在我的App类的OnLaunched方法中，我示例化了一个LoginUserControl，它将临时替换窗口的内容，我在类的一个字段中记住了窗口的原始内容。
• 当OnLaunched方法结束时，用户将看到以LoginUserControl为内容的窗口。
• 我的LoginUserControl将通过UserLoggedIn事件或UserAbortedLogIn事件关闭。
• 如果登录中止（不成功），我将通过关闭窗口中止应用程序启动。
• 如果登录成功，我将向应用程序的其余部分发布一个UserLoginSuccessful事件，并将窗口内容重置为其原始内容（即用户登录后应看到的第一个内容）。

protected override async void OnLaunched(Microsoft.UI.Xaml.LaunchActivatedEventArgs args)
 {
     // Create NavigationRootWindow (main window of the application)
     NavigationRootWindow = new NavigationRootWindow();

     // Store current content of the window (will be used later after the login)
     _navigationRootWindowContent = NavigationRootWindow.Content;

     // Create LoginUserControl and attach event handlers
     LoginUserControl loginUserControl = new LoginUserControl();
     loginUserControl.UserLoggedIn += LoginUserControl_UserLoggedIn;
     loginUserControl.UserAbortedLogIn += LoginUserControl_UserAbortedLogIn;

     // Set LoginUserControl as content of the window and display the window.
     // In case of a successful login, the content will be replaced later by the original content of the window.
     NavigationRootWindow.Content = loginUserControl;
     NavigationRootWindow.Activate();
 }

 /// <summary>
 /// Login was aborted.
 /// </summary>
 private void LoginUserControl_UserAbortedLogIn(object sender, EventArgs e)
 {
     NavigationRootWindow.Close();
 }

 /// <summary>
 /// Login was successful.
 /// </summary>
 private void LoginUserControl_UserLoggedIn(object sender, UserLoggedInEventArgs e)
 {
     EventAggregator.GetEvent<UserLoginSuccessful>().Publish(e.LoginSuccessfulResult);

     // Restore window content to original content
     NavigationRootWindow.Content = _navigationRootWindowContent;
     NavigationRootWindow.Init();
 }