Developing plugins for SDR# .NET 5 desktop

Visual Studio 2019 Community 16.8.5
C#
SDR# Plugin SDK for .NET 5 https://airspy.com/download/

Latest SDR# versions need .NET 5 desktop runtime and plugin development is also changed from prev versions due change to .NET 5. For developing plugins for SDR# .NET 5 install the latest version of VS 2019 and enable in tools -> options

Show all .NET Core templates in the New project dialog
Use the preview Windows Forms designer for .NET Core apps

Create a new project using template Class Library - a project for creating a class library that targets .NET Standard or .NET Core

Add these lines to VS project file especially if you are going to use WinForm controls in plugin: <UseWindowsForms>true</UseWindowsForms>

<PropertyGroup>
   <TargetFramework>net5.0-windows</TargetFramework>
   <OutputType>Library</OutputType>
   <Platforms>AnyCPU</Platforms>
   <UseWindowsForms>true</UseWindowsForms>
    <GenerateAssemblyInfo>true</GenerateAssemblyInfo>
   <AssemblyName>SDRSharp.Plugin.Rdsi</AssemblyName>
</PropertyGroup>

change text in references property group (SDRSharp.Common ...) to:
<ItemGroup>
    <Reference Include="SDRSharp.Common">
      <SpecificVersion>False</SpecificVersion>
      <HintPath>..\lib\SDRSharp.Common.dll</HintPath>
      <Private>True</Private>
    </Reference>
    <Reference Include="SDRSharp.PanView">
      <SpecificVersion>False</SpecificVersion>
      <HintPath>..\lib\SDRSharp.PanView.dll</HintPath>
      <Private>True</Private>
    </Reference>
    <Reference Include="SDRSharp.Radio">
      <SpecificVersion>False</SpecificVersion>
      <HintPath>..\lib\SDRSharp.Radio.dll</HintPath>
      <Private>True</Private>
    </Reference>
</ItemGroup>

... and reload the project after editing VS project file.
... otherwise you get lots of errors when building the solution.

Add references to SDRSharp.Common and .Radio and .Panview. Create a directory e.g. vendor and copy files from SDR# Plugin SDK for .NET 5 lib folder.

// implement at least ISharpPlugin, ICanLazyLoadGui, ISupportStatus
// See the examples in SDR# .NET 5 plugin SDK

using SDRSharp.Common;
using SDRSharp.Radio;
using System.Windows.Forms;

namespace SDRSharp.Plugin.Rdsi
{
    public class RdsiPlugin : ISharpPlugin, ICanLazyLoadGui, ISupportStatus
    {
        private const string _displayName = "RDS";
        private ISharpControl _controlInterface;
        private RdsiPluginPanel _configGui;

        public string DisplayName
        {
            get { return _displayName; }
        }

        public UserControl Gui
        {
            get
            {
                LoadGui();
                return _configGui;
            }
        }

        public void Close()
        {
        }

public bool IsActive => true;

        public void Initialize(ISharpControl control)
        {
            _controlInterface = control;
           _configGui = new RdsiPluginPanel(_controlInterface);
            control.RegisterStreamHook((object)new RdsHwnd(_configGui), ProcessorType.RDSBitStream);
        }

        public void LoadGui()
        {
            if (_configGui == null)
            {
                _configGui = new RdsiPluginPanel(_controlInterface);
            }
        }
    }
}

For user control (GUI) I copied files (User control: RdsiPluginPanel cs, resx and designer files) from RDS logger plugin I had coded for older versions of SDR# (no Telerik, no .NET 5 https://github.com/OH1GIU-P/SDRSharp.Rdsiplugin). When building VS showed error message: dispose is not implemented, fix: RdsiPluginPanel.cs => view in designer.