Fix setting nullable Action parameters on components

[jontavakoli]

When passing an Action from one Component to another component if the value is null the code throws the following exception: System.ArgumentException: 'Delegate to an instance method cannot have null 'this'.'

This is caused by the generated code, because it tries to create an instance of the Action delegate instead of just passing the value along as it is:

Component A - Generated Code (A.razor.g.cs)

public partial class A : Microsoft.AspNetCore.Components.ComponentBase
    {
        protected override void BuildRenderTree(Microsoft.AspNetCore.Components.Rendering.RenderTreeBuilder __builder)
        {
            __builder.OpenComponent<B>(0);
            __builder.AddAttribute(1, "When", new System.Action(When));
            __builder.CloseComponent();
        }

	[Parameter]
	public Action When { get; set; }

}

Component A (A.razor)

@code{

	[Parameter]
	public Action When { get; set; }

}

<B When="@When" />

Component B (B.razor)

@code{

	[Parameter]
	public Action When { get; set; }

}

<span>Empty</span>

Is there a way to override the code generation logic to stop this __builder.AddAttribute(1, "When", new System.Action(When)); and instead do __builder.AddAttribute(1, "When", When);.

[javiercn]

@jontavakoli thanks for contacting us.

I'm not exactly sure what it is going on here, we'll take a look and update the issue accordingly. In general code generation is not an area where we provide knobs for users to tweak, I'm not an expert in the area, but I know we do all sort of tricks to make type inference and other things like that work, so if we need to change something here we'll have to look in more detail since it can have unexpected consequences.

[mkArtakMSFT]

Thanks for contacting us.
We're moving this issue to the Next sprint planning milestone for future evaluation / consideration. We will evaluate the request when we will planning the work for the next milestone. To learn more about what to expect next and how this issue will be handled you can read more about our triage process here.

[mkArtakMSFT]

Hi. Thanks for contacting us.
We're closing this issue as we haven't seen many reports of it.
You can learn more about our triage process and how we handle issues by reading our Triage Process writeup.

[captainsafia]

Re-opening since this was recently reported in #27578 and had a few thumbs up on it.