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blazor components blazor-server-side

Blazor

发布于 2020-10-11 20:59:19

I'm having an issue with a basic blazor project. I have a parent component and a child component with an event callback where I want it to pass back a type of T. The issue I'm having is that I have an error about converting MethodGroup to EventCallback. If I convert this to using Action then it works but I can't do it async which isn't ideal. Any ideas what I'm doing wrong?

Parent

<Child
DeleteCallback="@OnDelete"></Child>

public async Task OnDelete(T item)
{
}

Child

@typeparam T

[Parameter]
public EventCallback<T> DeleteCallback { get; set; }

 <a @onclick="() => DeleteCallback.InvokeAsync(item)"></a>

I've added a repo here explaining the problem. Looking at the Issues for Blazor, this should;ve been fixed in 2019. https://github.com/scott-david-walker/EventCallbackError

Questioner
scottdavidwalker
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16.4k 2020-12-07 22:49:54

You were close:

<ChildComponent Item="someModel" T="SomeModel" DeleteCallback="OnDeleteSomeModel" />

@code {
    SomeModel someModel = new SomeModel();

    void OnDeleteSomeModel(SomeModel someModel)
    {
        ...
    }
}

The EventCallback uses a generic type and blazor cannot infer it if you don't pass the type to the component.

This means that if you have a EventCallback<T> you need to pass the value of T to the component e.g. T="SomeType".

Brian Parker 2020-10-12 09:32:51

I found the issue its because your using a templated component it is having trouble with the public EventCallback<T> DeleteCallback, You need to declare the type of T not just infer it by usage. I'll update my answer

scottdavidwalker 2020-10-12 11:15:13

That did the trick, cheers for the help. That was an annoying one :-)

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