Async OnActionExecuting in ASP.NET Core's ActionFilterAttribute

c# asp.net-core action-filter
grokky picture grokky · May 15, 2017 · Viewed 25.3k times · Source

ASP.NET Core's ActionFilterAttribute has these:

public virtual void OnActionExecuting(ActionExecutingContext context);
public virtual void OnActionExecuted(ActionExecutedContext context);
public virtual Task OnActionExecutionAsync(ActionExecutingContext context, ActionExecutionDelegate next);

I need an async version of OnActionExecuting, which doesn't exist.

However I have a feeling that I can use OnActionExecutionAsync instead, as it also has an argument of ActionExecutingContext.

Am I correct that despite the name, they trigger at the same point in the process?

Also, what do I need to do with the next argument? Once I'm done with my stuff, do I simply need to call await next()?

Is that it? I'm unsure as I can't find docs for this.

Answer

jeroenh picture jeroenh · May 15, 2017

Asynchronous filters work a bit differently: first execute code that must be executed before the action, call next() for the actual logic, finally add code to be executed after the action.

public async Task OnActionExecutionAsync(ActionExecutingContext context, 
                                         ActionExecutionDelegate next)
{

    // logic before action goes here

    await next(); // the actual action

    // logic after the action goes here
}

The documentation is here: https://docs.microsoft.com/en-us/aspnet/core/mvc/controllers/filters#implementation

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