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>
      };
}

Akinzekeel · Accepted Answer · 2020-11-08 16:40:36Z

2

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>
};

edited Nov 8, 2020 at 16:40

answered Nov 8, 2020 at 16:17

Akinzekeel

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6 Comments

My Helper Over a year ago

That worked. You probably wanna fix the typo "rf()" to "rf". Thanks a lot!

dani herrera Over a year ago

Notice than now it's not reusing rendering logic because you get new logic each time you use it. You don't get the extra performance.

Akinzekeel Over a year ago

@daniherrera I suppose what you could do is override OnInitialized() and then assign the RenderFragment there once.

dani herrera Over a year ago

Maybe a getter

My Helper Over a year ago

@daniherrera can't I make it static so that it gives me the same instance all the time & I can still benefit from the performance? (Please note in the article I linked has the recommendation to make the RenderFragment static to be shared across multiple pages). Thank you!

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