Allow property navigation for ChildComponent rendering when using CascadingTypeParameter

[BrunoBlanes]

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

I am trying to simplify my Table component design for the consumer of my library. Currently it is implemented as follows:

Table.razor

@using Microsoft.AspNetCore.Components.Web.Virtualization

@typeparam TItem
@attribute [CascadingTypeParameter(nameof(TItem))]

<CascadingValue IsFixed="true" Value="this">@ChildContent</CascadingValue>

<div class="table-container column">
    <Virtualize Items="Items" Context="item">
        @foreach (var column in columns)
        {
            @column.GetValue(item)
        }
    </Virtualize>
</div>

@code {
    private List<TableColumn<TItem>> columns = new();

    [Parameter]
    public RenderFragment? ChildContent { get; set; }

    [Parameter]
    public ICollection<TItem>? Items { get; set; }

    internal void AddTableColumn(TableColumn<TItem> column)
    {
	columns.Add(column);
    }
}

TableColumn.cs

public partial class TableColumn<TItem> : ComponentBase
{
    private Func<TItem, object>? compiledExpression;

    [CascadingParameter]
    public Table<TItem>? Table { get; set; }

    [Parameter]
    public Expression<Func<TItem, object>?>? Expression { get; set; }

    protected override void OnInitialized()
    {
	Table?.AddTableColumn(this);
	base.OnInitialized();
    }

    internal object? GetCellValue(TItem item)
    {
	ArgumentNullException.ThrowIfNull(compiledExpression);
	return compiledExpression(item);
    }
}

Usage

<Table Items="group?.Blocks">
    <TableColumn Expression="block => block.Name" />
    <TableColumn Expression="block => block.Id" />
    <TableColumn Expression="block => block.Group" />
</Table>

Describe the solution you'd like

I'd like for the end user to be able to define the table as follows:

<Table Items="group?.Blocks" Context="block">
    <TableColumn>@block.Name</TableColumn>
    <TableColumn>@block.Id</TableColumn>
    <TableColumn>@block.Group</TableColumn>
</Table>

I've tried a few things, but the way RenderFragment seems to be implemented now doesn't allow this to work.

Additional context

I've been looking around for topics on this issue and found #29379 which is related but I don't think addresses this specificly.

[javiercn]

@BrunoBlanes thanks for contacting us.

You can already do this by passing a RenderFragment instead of a RenderFragment. It's not clear that we are missing anything here.

Your child content in Table.razor as well as in TableColum.razor need to be RenderFragment<T>, but afterwards, it should work.

[BrunoBlanes]

Thanks, with your help and the help of this article I got it working. I'm gonna go dig myself a hole to cry on in fetal position for all the hours I spent on trial and error now...

[BrunoBlanes]

Quick question, is it possible to know when @ChildContent(T) will return string.Empty or null?