设置事件回调<string>在 Blazor 组件之外？

Question

I am building a Blazor ProgressBar demo, and I am attempting to move some code out of my Blazor component into a C# class called ProgressManager. This is so I can abstract the code and make the ProgressManager a CascadingParameter to the ProgressBar component.

I know how to set an EventCallback parameter for a component like this:

[Parameter]
public EventCallback<string> UpdateNotification { get; set; }

What I don't know how to do is set this same type of property on a C# class.

I have this code in my Start method:

public void ShowProgressSimulation()
{
    // Create a ProgressManager
    this.ProgressManager = new ProgressManager();
    this.ProgressManager.UpdateNotification = Refresh;
    this.ProgressManager.Start();
    
    // Refresh the UI
    StateHasChanged();
}

The part that does not work is: this.ProgressManager.UpdateNotification = Refresh;

The error is:

Cannot convert method group 'Refresh' to non-delegate type 'EventCallback'. Did you intend to invoke the method?

I also tried: this.ProgressManager.UpdateNotification += Refresh;

And this leads to "EventCallback cannot be applied to method group" (paraphrasing).

Answer 1

Turns out you can assign an event callback from C# code like this:

this.ProgressManager.UpdateNotification = new EventCallback(this, (Action)Refresh);

void Refresh() {}

It also works with async methods, eg:

this.ProgressManager.UpdateNotification = new EventCallback(this, (Func<ValueTask>)RefreshAsync);

ValueTask RefreshAsync() {}

UPDATE

You can also use EventCallbackFactory to more conveniently create event callback objects, eg:

new EventCallbackFactory().Create(this, Refresh)

Answer 2

您还可以使用以下代码通过工厂创建EventCallBack ，而无需新建EventCallbackFactory

Button.Clicked = EventCallback.Factory.Create( this, ClickHandler );