Blazor Render Fragment Child Content to allow only certain components?

Question

Is it possible to restrict the RenderFragment Child Content of a component to only allow certain components? For example

<MyParentComponent>
 <Children>
  <AcceptedChild/>
  <InvalidChild/> <-- throw err since it shouldn't be accepted
 </Children>
</MyParentComponent>

EDIT:

<DataGrid>
 <DataGridColumns>
  <DataGridColumn/>
  <DataGridColumn/>
  <NotADataGridColumn/> <--- throw error
 </DataGridColumns>
</DataGrid>

Answer 1

Is it possible to restrict the RenderFragment Child Content of a component to only allow certain components?

No.

A RenderFragment is a delegate. In your example the RenderFragment assigned to DataGridColumns belongs to the parent page/component, not DataGrid, and is run in the context of the parent by the Renderer. DataGrid only "knows" it as a delegate that conforms to the RenderFragment pattern. It has no access to the internal code, so has no way of knowing what it contains.

Answer 2

If your component contains two or more RenderFragment parameters, you can limit the valid selection of direct children when using your component.

E.g. if you have a component MyComponent with the following parameters:

[Parameter]
public RenderFragment FirstChild { get; set; }

[Parameter]
public RenderFragment SecondChild { get; set; }

and you try to use it as follows:

<MyComponent>
    <FirstChild />
    <SecondChild />
    <ThirdChild />
</MyComponent>

<ThirdChild /> will throw error:

RZ9996 Unrecognized child content inside component 'MyComponent'. The component 'MyComponent' accepts child content through the following top-level items: 'MyFirstChildComponent', 'MySecondChildComponent'.

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The equivalent in your example would be that Children e.g. contains parameters RenderFragment AcceptedChild and RenderFragment AcceptedChild2, but no RenderFragment InvalidChild.