Blazor Reusable RenderFragments in code with event : Cannot convert lambda expression to intended delegate type

Question

Anyone knows why the below doesn't work? If I remove "onclick" event then it compiles & works as expected. Is that we are not allowed to use event within Reusable RenderFragments?

Env: ASP.NET Core 3.1 & Blazor Web Assembly

Thanks a lot for the help in advance!

Cannot convert lambda expression to intended delegate type because some of the return types in the block are not implicitly convertible to the delegate return type

@code {
    RenderFragment<(CategoryDto category, int myId)> rf =
      val => __builder =>
      {
        <h1 @onclick="()=> Console.WriteLine(val.category.Name)">Hello @val.category.Name, @val.myId</h1>
      };
}

Answer 1

The @onclick handler in your code will ultimately be created by the EventCallbackFactory. However, that factory needs a reference to 'this' which isn't supported in field initializers - hence you are receiving this error (and probably another one regarding 'this').

The solution is pretty simple. You just need to turn the field into a property like so:

RenderFragment<(CategoryDto category, int myId)> rf => val => __builder =>
{
    <h1 @onclick="() => Console.WriteLine(val.category.Name)">Hello @val.category.Name, @val.myId</h1>
};