Struggling around with RenderFragement<T> returning a Detail Template for a razor base component

Question

I try to implement a generic razor base component, but cannot find out the correct syntax when passing the context to the child. This is my base class

@typeparam T where T : class
....
<GridColumns>
  @Columns
</GridColumns
....
<DetailTemplate>
   @Deatil((T) context)
</DetailTemplate>

@code {
  protected override RenderFragment Columns { get; }
  protected override RenderFragment<T> Detail { get; } 

And in my derived child I try to define those templates,

 protected override RenderFragment Columns
{
    get
    {
        return __builder =>
        {
            <GridColumn Field="Id" Title="#" />
            <GridColumn Field="Name" />
            .....
        };
    }
}

This is working, however I can't find out how to provide the template for the detail

protected override RenderFragment<T> Detail => currentT => __builder =>
{
    get             // <== compiler claims a missing ; here
    {
        return __builder =>
        {
            if (currentT.ParentId == null)
            {
                <h1>One</h1>
            }
            else
            {
                <h1>Two</h1>
            }
        };
    };
};

Can anyone point me in the right direction?

Answer 1

You don't need to use get, the third => defines the getter implicitly. There is also no return value. RenderFragment is a delegate defined as follows:

public delegate void RenderFragment(RenderTreeBuilder builder);

As there's not enough detail to use your code, here's an example of how to build and consume a RenderFragment<T> using Razor markup.

@page "/fetchdata"
@using Blazr.Data
@inject WeatherForecastService ForecastService

<PageTitle>Weather forecast</PageTitle>

<h1>Weather forecast</h1>

<p>This component demonstrates fetching data from a service.</p>

@if (forecasts == null)
{
    <p><em>Loading...</em></p>
}
else
{
    <table class="table">
        <thead>
            <tr>
                <th>Date</th>
                <th>Temp. (C)</th>
                <th>Temp. (F)</th>
                <th>Summary</th>
            </tr>
        </thead>
        <tbody>
            @foreach (var forecast in forecasts)
            {
                @Detail(forecast)
            }
        </tbody>
    </table>
}

@code {
    private WeatherForecast[]? forecasts;

    protected override async Task OnInitializedAsync()
    {
        forecasts = await ForecastService.GetForecastAsync(DateOnly.FromDateTime(DateTime.Now));
    }

    protected RenderFragment<WeatherForecast> Detail
        => context => __builder =>
            {
                <tr>
                    <td>@context.Date.ToShortDateString()</td>
                    <td>@context.TemperatureC</td>
                    <td>@context.TemperatureF</td>
                    <td>@context.Summary</td>
                </tr>
            };
}