Windows Forms Lifetime

2022-02-23

This post will go over the Windows Forms Lifetime library I’ve started writing. The library is a Windows Forms hosting extension for the .NET Generic Host. It enables you to configure the generic host to use the lifetime of Windows Forms, aka when the main Form closes, the host will shut down.

https://github.com/alex-oswald/WindowsFormsLifetime

Get started with .NET 6’s Minimal API

Create a new Windows Forms App.

Change the projects SDK to Microsoft.NET.Sdk.Web so we can use the WebApplication class.

Add NoDefaultLaunchSettingsFile to the csproj so a launchSettings.json file isn’t created automatically for us.

<Project Sdk="Microsoft.NET.Sdk.Web">
  <PropertyGroup>
    <OutputType>WinExe</OutputType>
    <TargetFramework>net6.0-windows</TargetFramework>
    <Nullable>enable</Nullable>
    <UseWindowsForms>true</UseWindowsForms>
    <ImplicitUsings>enable</ImplicitUsings>
    <NoDefaultLaunchSettingsFile>true</NoDefaultLaunchSettingsFile>
  </PropertyGroup>
</Project>

Replace the contents of Program.cs with the following.

using WinFormsApp1;

var builder = WebApplication.CreateBuilder(args);
builder.Host.UseWindowsFormsLifetime<Form1>();
var app = builder.Build();
app.Run();

Instantiating and Showing Forms

Add more forms to the DI container.

using WinFormsApp1;

var builder = WebApplication.CreateBuilder(args);
builder.Host.UseWindowsFormsLifetime<Form1>();
builder.Services.AddTransient<Form2>();
var app = builder.Build();
app.Run();

To get a form use the IFormProvider. The form provider instantiates an instance of the form from the DI container on the GUI thread. IFormProvider has one method, GetFormAsync<T> used to fetch a form instance.

In this example, we inject IFormProvider into the main form, and use that to instantiate a new instance of Form, then show the form. Instantiating a Form directly in a nother form will also create it on the GUI thread, but using the IFormProvider is best practice when using this library.

public partial class Form1 : Form
{
    private readonly ILogger<Form1> _logger;
    private readonly IFormProvider _formProvider;

    public Form1(ILogger<Form1> logger, IFormProvider formProvider)
    {
        InitializeComponent();
        _logger = logger;
        _formProvider = formProvider;
    }

    private async void button1_Click(object sender, EventArgs e)
    {
        _logger.LogInformation("Show Form2");
        var form = await _formProvider.GetFormAsync<Form2>();
        form.Show();
    }
}

Invoking on the GUI thread

Sometimes you need to invoke an action on the GUI thread. Say you want to spawn a form from a background service. Use the IGuiContext to invoke actions on the GUI thread.

In this example, a form is fetched and shown every 5 seconds 5 times, in an action that is invoked on the GUI thread. This example shows how the GUI thread does not lock up during this process.

public class HostedService1 : BackgroundService
{
    private readonly IFormProvider _fp;
    private readonly IGuiContext _guiContext;

    public HostedService1(
        IFormProvider formProvider,
        IGuiContext guiContext)
    {
        _fp = formProvider;
        _guiContext = guiContext;
    }

    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        int count = 0;
        while (!stoppingToken.IsCancellationRequested)
        {
            await Task.Delay(5000, stoppingToken);
            if (count < 5)
            {
                await _guiContext.InvokeAsync(async () =>
                {
                    var form = await _fp.GetFormAsync<Form2>();
                    form.Show();
                });
            }
            count++;
        }
    }
}

Conclusion

I’ve explained that the WindowsFormsLifetime library lets you use .NET’s Generic Host with Windows Forms application, and how it can control the lifetime of the application. I demonstrated how to get started using .NET 6’s Minimal API. I also showed the two main services that come with the library, the IFormProvider which is used to new up forms on the GUI thread, and the IGuiContext which is used to invoke actions on the GUI thread to prevent cross-thread exceptions.

In a future post, I will demonstrate how to use the WindowsFormsLifetime.Mvp companion library to develop Model-View-Presenter applications using Windows Forms.

Until then, happy win forming!