I use constructor-based dependency injection everywhere in my ASP.NET CORE
application and I also need to resolve dependencies in my action filters:
public class MyAttribute : ActionFilterAttribute
{
public int Limit { get; set; } // some custom parameters passed from Action
private ICustomService CustomService { get; } // this must be resolved
public MyAttribute()
{
}
public override async Task OnActionExecutionAsync(ActionExecutingContext context, ActionExecutionDelegate next)
{
// my code
...
await next();
}
}
Then in Controller:
[MyAttribute(Limit = 10)]
public IActionResult()
{
...
If I put ICustomService to the constructor, then I'm unable to compile my project. So, how do I supossed to get interface instances in action filter?
If you want to avoid the Service Locator pattern you can use DI by constructor injection with a TypeFilter
.
In your controller use
[TypeFilter(typeof(MyActionFilterAttribute), Arguments = new object[] {10})]
public IActionResult() NiceAction
{
...
}
And your ActionFilterAttribute
does not need to access a service provider instance anymore.
public class MyActionFilterAttribute : ActionFilterAttribute
{
public int Limit { get; set; } // some custom parameters passed from Action
private ICustomService CustomService { get; } // this must be resolved
public MyActionFilterAttribute(ICustomService service, int limit)
{
CustomService = service;
Limit = limit;
}
public override async Task OnActionExecutionAsync(ActionExecutingContext context, ActionExecutionDelegate next)
{
await next();
}
}
For me the annotation [TypeFilter(typeof(MyActionFilterAttribute), Arguments = new object[] {10})]
seems to be awkward. In order to get a more readable annotation like [MyActionFilter(Limit = 10)]
your filter has to inherit from TypeFilterAttribute
. My answer of How do I add a parameter to an action filter in asp.net? shows an example for this approach.