C# – Action vs delegate event

cdelegates

I have seen developers using the below codes quite alternatively. What is the exact difference between these, and which ones go by the standard? Are they same, as Action and Func<T> is a delegate as well:

public event Action<EmployeeEventAgs> OnLeave;
public void Leave()
{
    OnLeave(new EmployeeEventAgs(this.ID));
}

public delegate void GoOnLeave(EmployeeEventAgs e);
public event GoOnLeave OnLeave;
public void Leave()
{
    OnLeave(new EmployeeEventAgs(this.ID));
}

Best Answer

Fwiw, neither example uses standard .NET conventions. The EventHandler<T> generic should declare the event:

public event EventHandler<EmployeeEventArgs> Leave;

The "On" prefix should be reserved for a protected method that raises the event:

protected virtual void OnLeave(EmployeeEventArgs e) {
    var handler = Leave;
    if (handler != null) handler(this, e);
}

You don't have to do it this way, but anybody will instantly recognize the pattern, understand your code and know how to use and customize it.

And it has the great advantage of not being forced to choose between a custom delegate declaration and Action<>, EventHandler<> is the best way. Which answers your question.

Related Solutions

C# – Func delegate with no return type

All Func delegates return something; all the Action delegates return void.

Func<TResult> takes no arguments and returns TResult:

public delegate TResult Func<TResult>()

Action<T> takes one argument and does not return a value:

public delegate void Action<T>(T obj)

Action is the simplest, 'bare' delegate:

public delegate void Action()

There's also Func<TArg1, TResult> and Action<TArg1, TArg2> (and others up to 16 arguments). All of these (except for Action<T>) are new to .NET 3.5 (defined in System.Core).

C# – Action returning void and taking parameter, with ternary operator

You'll need to cast one side or other - or not use the conditional operator.

Basically, ignore the assignment - because the compiler does. It doesn't use the fact that you're trying to assign to a variable to work out the type of the conditional expression. We're left with just:

(i > 5) ? action1 : action2

as the expression. What's the type of that? What delegate type should the method groups be converted to? The compiler has no way of knowing. If you cast one of the operands, the compiler can check that the other can be converted though:

(i > 5) ? (Action<PerformanceCounterCategory>) action1 : action2

Alternatively:

Action<PerformanceCounterCategory> action = action2;
if (i > 5)
{
    action = action1;
}

It's unfortunate, but that's life I'm afraid :(

Best Answer

Related Solutions

C# – Func delegate with no return type

C# – Action returning void and taking parameter, with ternary operator

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