samples/windowsforms

.NET Core 3.1 Windows Forms Samples

With .NET Core 3.1, you can build Windows Forms applications.

Why build Windows Forms applications on top of .NET Core

If you're new to .NET Core, here are a few resources to help you understand the advantages of .NET Core for building Windows applications:

• Blog: .NET Core 3 and Support for Windows Desktop Applications
• Video: Modernizing Desktop Apps on Windows 10 with .NET Core 3.0 and much more

Quality disclaimer

.NET Core 3 support for desktop development is in preview. There are early daily builds available supporting Windows Forms and WPF. You will likely encounter missing tools, bugs, and unexpected behavior. We do not recommend using this SDK and tools for building applications for production scenarios. We do recommend using this SDK and tools to evaluate your how easy it will be to migrate your existing applications, or if you're just interested in trying out the latest upcoming Windows development technology.

Samples in this repo

Sample Name	Description
Hello World - shared source	This sample shows you how to share source between a .NET Framework Windows Forms application and a .NET Core Windows Forms application. Use this to get the full .NET Framework tooling experience while still building for .NET Core.
Matching Game	This sample demonstrates simple event handling and timers in a .NET Core 3 Windows Forms application
DataGridView Sample	This sample demonstrates DataGridView usage in .NET Core 3
Graphics Sample	This sample demonstrates using GDI+ APIs via the Graphics type in .NET Core 3
Sudoku Sample	This sample demonstrates creating a game using event handling and the Graphics type in .NET Core 3
Conway's Game of Life Sample	This sample demonstrates creating a DataGridView extension to handle OnRowPrePaint and trapping Windows Messages to prevent a left mouse click in .NET Core 3

Getting Started

Prerequisites and getting the tools

Visual Studio 2019 Version 16.5.0 Preview 2.0 or later from https://visualstudio.microsoft.com/vs/preview, selecting the .NET desktop development workload with the options: .NET Framework 4.7.2 development tools and .NET Core 3.1 development tools.

Install the latest .NET Core 3.1 SDK released or daily build available in the dotnet/code-sdk repo.

Analyzing your application's for .NET Core 3.1 readiness

If you want to first understand your existing applications readiness for targeting .NET Core 3.1 or later, you can run the .NET Portability Analyzer using the download link and instructions here. This will produce a report that shows you API compatibility for each assembly that your application depends on.

Creating new .NET Core 3.1 or later Windows Forms applications

To create a new application you can use the dotnet new command, using the new templates for Windows Forms.

In your favorite console run:

dotnet new winforms -o MyWinFormsApp
cd MyWinFormsApp
dotnet build
dotnet run

Enable Windows Forms designers

The Windows Forms designer for .NET Core 3 in Visual Studio is in preview and must be enabled. To enable the designergo to Tools > Options > Environment > Preview Features and select the Use the preview Windows Forms designer for .NET Core apps option.

Porting existing applications

We recommend running the APIPort tool first to determine if there are any APIs your application depends on that are missing with .NET Core.

There is no tooling available to help with project migration. In order to migrate your Windows Forms application, you will create a new project and manually port all of the elements defined in your original project. You will notice the new project is based on the simplified project format, and not everything is migrated.

Migrate the head project

Ideally you should migrate all projects in your solution to target .NET Core 3.1 and/or .NET Standard 2.0. The first step to migrate will be to retarget the application's entry point (i.e., 'head' project) and maintain your existing references.

1. Start from a working Solution. You must be able to open the solution in Visual Studio and double check that you can build and run without any issues.

2. If your solution also has server-side projects, such as ASP.NET, we recommend splitting your solution into different server and client solutions. For this effort, work with the client solution only.

3. Add a new .NET Core 3.1 Windows Forms project to the solution. Adding this project to a sibling folder to your existing 'head' project will make it easier to port references later (using relative paths to other projects or assemblies in the solution)

4. If your 'head' project uses NuGet packages, you must add the same NuGet packages to the new project. The new SDK-Style projects only support the PackageReference format for adding NuGet package references. If your existing project uses packages.config, you must migrate to the new format. You can use the Migrator Tool described here to automate this process.

5. Copy the PackageReference elements generated in the previous step from the original project into the new project's .csproj file.

6. Copy the ProjectReference elements from the original project. Note: The new project format does not use the Name and ProjectGuid elements, so you can safely delete those.

7. At this point it's a good idea to try and restore/build to make sure all dependencies are properly configured.

8. Link the files from your existing .NET Framework Windows Forms project to the .NET Core 3.1 Windows Forms project.

9. Optional If you have difficulties with compiler linking, you can copy the project files from the .NET Framework Windows Forms project to the new .NET Core 3.1 Windows Forms project.

   • C# files (files with the .cs extension) are included by default in the .csproj.
   • Other project elements like EmbeddedResources can also use globbing.

Migration tips

Configure assembly file generation

Most existing projects include an AssemblyInfo.cs file in the Properties folder. The new project style uses a different approach and generates the same assembly attributes as part of the build process. To disable that behavior you can add the property:

<GenerateAssemblyInfo>false</GenerateAssemblyInfo>

Include the Windows.Compatibility Pack

Not every framework assembly is available in the .NET Core base class library. Windows applications like Windows Forms and WPF could have dependencies that are not available in .NET Core or .NET Standard. Adding a reference to the Windows Compatibility Pack will help reduce missing assembly dependencies as it includes several types that might be needed by your application.

dotnet add package Microsoft.Windows.Compatibility

Link Files from the old project

Visual Studio does not yet support designers and custom tools for .NET Core desktop development. You can keep your files in the original project and link the generated files to the new project by using the link attribute in the project elements, e.g. <Compile Link="" />. See the sample in this repo for an example of this.

Migrating WCF clients

.NET Core has its own implementation of System.ServiceModel with some differences:

• It's available as NuGet packages (also included in the Windows Compatibility Pack).
• There are unsupported features that you should review.
• The binding and endpoint address must be specified in the service client constructor. Otherwise, if you reuse the ServiceReference created by Visual Studio, you may get the following error: System.PlatformNotSupportedException: 'Configuration files are not supported.'

Filing issues and getting help

You can file Windows Forms and WPF related issues in the dotnet/core repo. If you are trying out WPF or Windows Forms development on top of .NET Core 3.1 and get stuck or have questions, reach out to netcore3modernize@microsoft.com.

Known issues

Take a look at the issues filed with the WinForms area tag.