The MainWindow shown manually raises error on running application in WPF Blazor

Question

Considering the sample code below:

Counter.razor:

<h1>Counter</h1>
<p>Current count: @currentCount</p>
<button class="btn btn-primary" @onclick="IncrementCount">Click me</button>

@code {
    private int currentCount = 0;

    private void IncrementCount()
    {
        currentCount++;
    }
}

MainWindow.xaml:

<Window x:Class="WpfBlazor.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:blazor="clr-namespace:Microsoft.AspNetCore.Components.WebView.Wpf;assembly=Microsoft.AspNetCore.Components.WebView.Wpf"
    xmlns:local="clr-namespace:WpfBlazor"
    mc:Ignorable="d"
    Loaded="Window_Loaded"
    Title="MainWindow" Height="450" Width="800">
<Grid>
    <blazor:BlazorWebView Name="webView" HostPage="wwwroot\index.html" Services="{DynamicResource services}">
        <blazor:BlazorWebView.RootComponents>
            <blazor:RootComponent Selector="#app" ComponentType="{x:Type local:Counter}" />
        </blazor:BlazorWebView.RootComponents>
    </blazor:BlazorWebView>
</Grid>

MainWindow.xaml.cs

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();

        var serviceCollection = new ServiceCollection();
        serviceCollection.AddWpfBlazorWebView();
        Resources.Add("services", serviceCollection.BuildServiceProvider());
    }
}

App.xaml.cs:

using System.Windows;

namespace WpfBlazor
{
    public partial class App : Application
    {
        [STAThread]
        public static void Main()
        {
            var app = new App();
            app.InitializeComponent();
            var window = new MainWindow();
            window.Show();
            app.Run();
        }
    }
}

It raises the following error on app.Run():

"EnsureCoreWebView2Async cannot be used before the application's event loop has started running."

It works if I do it in this way, but I can't, since it's a sample code, and in the real situation I need to separate instantiation and showing the window from the app.Run():

var window = new MainWindow();
app.Run(window);

I have tried calling the await window.webView.WebView.EnsureCoreWebView2Async(null); in app startup and window loaded but it didn't work.

Answer 1

...and in the real situation I need to separate instantiation and showing the window from the app.Run():

You should still start the app before showing the window. Call the Run method of the App in your Main method and then override the OnStartup method of the App class to customize the initialization of the window:

[STAThread]
public static void Main()
{
    App application = new App();
    application.Run();
}

protected override void OnStartup(StartupEventArgs e)
{
    base.OnStartup(e);

    var window = new MainWindow();
    window.Show();
}