Passing additional data to Generic RenderFragment in Blazor component

user_826402 0
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I have a simple Blazor component which iterates over a Generic List :

@typeparam TItem;

 @foreach (var item in List)
        {
            @ElementTemplate(item); // What code should be here to pass i to the ElementTemplate????
            i++;
        }

@code {
    int i = 0;


    [Parameter] public List<TItem> List { get; set; }
    [Parameter] public RenderFragment<TItem> ElementTemplate { get; set; }
  }

I have another simple component which will get an item and an index to render data(Employee):

<div> @Index . @Person.Name </div>

@code{
    [Parameter] public Person { get; set; }
    [Parameter] public int Index { get; set; }

}

And in my main page I have the following:

<GenericList List="employees">
    <ElementTemplate>
        <Employee Person="context" Index="?"></Employee>
    </ElementTemplate>
</GenericList>

As you can see Employee component needs an Index parameter, how can I pass the Index from the GenericList component? In this example the variable 'i' should be passed to ElementTemplate as well as the Generic TItem object itself.

blazor asp.net-core generics c#
2 Answers

I find the quick/simple approach is to use a tuple as the RenderFragment context:

@foreach (var item in List)
{
  @ElementTemplate((item,i));
  i++;
}

@code {
  int i=0;
  [Parameter] public List<TItem> List { get; set; }
  [Parameter] public RenderFragment<(TItem item, int index)> ElementTemplate { get; set; }
}

Then your markup becomes:

<GenericList List="employees">
    <ElementTemplate>
        <Employee @key=@context.index Person=@context.item Index=@context.index></Employee>
    </ElementTemplate>
</GenericList>

If you prefer, you could use a utility class in the GenericList instead of a tuple.

user_26586970

You can define a complex class for your Context

In the GenericList.razon, define a class:

public class ListContext
{
    public TItem Item {get; set;}
    public int Index {get; set;}
}

and use this class as a context type for your template:

[Parameter] 
public RenderFragment<ListContext> ElementTemplate { get; set; }

then when you call this template, you can just create a new class and set the correct parameters:

@foreach (var item in List)
{
    @ElementTemplate(new ListContext{Item = item, Index = i});
    i++;
}

here is a working example of this: https://blazorrepl.com/repl/cuvakzPF21sXSZGK54

user_36853450
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