Add ability to pass @typeparam down to child components

[ivanchev]

Is your feature request related to a problem? Please describe.

If you have a templated component, that's Generic and uses @typeparam, if you want to add other child components, you also have to specify the type when you declare them. For instance in a Grid:

<Grid Data=List<Item>>
  <Columns>
    <Column TItem=Item>
      <Template />
    </Column>
  </Columns>
</Grid>

In this setup, in order to have a strongly typed context passed to the Column templates, you have to specify explicitly TItem to each Column and cannot be inferred by the List.

Describe the solution you'd like

With the current setup we can pass simple parameters down to child components with:

<CascadingValue Value=this>
    @Columns
</CascadingValue>

I would like to have the ability to aslo pass down @typeparam values. Perhaps something like:

<CascadingType Value=TItem>
    @Columns
</CascadingType>

And if the child component declares it's own TItem, it will override the Cascading value.

[SteveSandersonMS]

I agree with the needs-design label!

It's not clear to me what the right design for this would be, or even if it's possible at all. If the outer component obtained its generic type through inference, then the generated code doesn't know about it at all prior to compilation. So I'm not clear that it's possible to pass it to nested components.

@rynowak Am I missing any obvious possible solution? Do you have any ideas about how something like this could be achieved? Or if not, any thoughts on an alternative feature we might be able to offer to achieve a similar goal of determining generic types based on tag hierarchy? Better still would be inferring generic types based on cascading parameters, but I don't see how that would be possible given that we don't know about cascading parameters until runtime.

[ivanchev]

If inference is the main problem, having to specify the type on the main component explicitly is still a viable option, as long as it's only specified in just one place.

[EdCharbeneau]

I'm glad to see a milestone for this. We (Telerik) have been getting requests for this feature from customers. The description is generally "Please add HTML helper like model binding intellisense". This is definitely something developers want.

Here is one such example: Check out @robertmclaws’s Tweet: https://twitter.com/robertmclaws/status/1106267471965798411?s=09