Question

I am currently working with an ASP.NET MVC 4 project, using C#.

I would like to create an extension method that accepts various types of methods, wraps those methods in a try/catch, and then returns the results of the method call if the call succeeds.

Here is what I have so far:

  public static object HandleServerError(this object obj)
        {
            object result = null;
            try
            {
                result = obj;
            }
            catch (Exception ex)
            {
                ErrorHandlers.ThrowServerErrorException(ex);
            }

            return result;
        } 

Here is an example of the extension method in use:

var test = webClient.DownloadString(uri).HandleServerError().ToString();

This works ok, but the webClient.DownloadString(uri) part is executed and then passed into HandleServerError as a string which is NOT what I want.

What I am wanting to do is INJECT webClient.DownloadString(uri) into the extension method so that the actual method call is wrapped into a try/catch.

Please note

I realize that there are arguments against try/catch statements, but not looking to start a debate over the subject–the core of this question is centered on the dependency injection problem. Thanks for all answers though!

Answer 1

You need to create an extension method for a callback (a Func<T>), not an object.

Something like this:

static class FuncExtensions  {
    public static T HandleServerError<T>(this Func<T> func) {
        T result = default(T);
        try {
            result = func();
        }
        catch (Exception ex) {
            // Handle exception here.
        }
        return result;
    }
}

And in use it would look something like this:

new Func<string>(() => webClient.DownloadString(uri)).HandleServerError();

But this whole thing would probably be better implemented with a regular method call than extension methods.