Winforms designer does not work after update to preview 3

Question

Hi,

Ik made a small winform test in preview 2 with .net5. Now installed preview 3 and I can't open a form anymore in de designer. the error is:

Unable to find method 'InitializeAsync/1' on {no object} for the following reasons: Deserializing JSON-RPC argument with name "options" and position 0 to type "Microsoft.DotNet.DesignTools.Protocol.Server.ServerInitializationOptions" failed: Expected JSON token PropertyName, but it was EndObject.

I found the same question here but it has not been answered yet. So I hope that some here knows a solution.

Greetings

Answer 1

Hi,

I tried to start a new project and that failed to. But after I repaired the Visual studio installation the error is gone. Everything seems to work fine now.
Repairing the installation was the solution.

Greetings

Answer 2

Hello,

.NET 5 is out of preview, see the following download page.

If you double click on the project file in Solution Explorer you should have the following for C# 9, .NET5

<Project Sdk="Microsoft.NET.Sdk">  
  
	<PropertyGroup>  
		<OutputType>WinExe</OutputType>  
		<LangVersion>latest</LangVersion>  
		<TargetFramework>net5.0-windows</TargetFramework>  
		<RootNamespace>Async_Enumerables</RootNamespace>  
		<UseWindowsForms>true</UseWindowsForms>  
	</PropertyGroup>  
</Project>  

Under the project properties

Important

Once the following has been done

• Right click on the project in solution explorer, select clean.
• Right click on the project in solution explorer, select build.

Make sure there is a reference to System.Text.Json which can be using NuGet using this package or for Json.NET use this package.

Answer 3

Hi,

In Options I had .net5 selected. I tried clean and build. The program was already building well. I changed the first line and this is now a part of my project file:

<Project Sdk="Microsoft.NET.Sdk">  (This line was: <Project Sdk="Microsoft.NET.Sdk.WindowsDesktop">)

  <PropertyGroup>
    <OutputType>WinExe</OutputType>
    <TargetFramework>net5.0-windows</TargetFramework>
    <UseWindowsForms>true</UseWindowsForms>    
    <Platforms>AnyCPU;x64</Platforms>
  </PropertyGroup>

  ...

</Project>  

I now got the system.txt.json with the nuget package manager. (using System.Text.Json; did work without it)

I still can't open a form. I get the same error.

Greetings