C# - Can someone tell me why and where I should use delegates? [duplicate]

Answer 1

Is there an advantage to use a delegate when dealing with external calls to a database?

For example can code A :

static void Main(string[] args) {

           DatabaseCode("test");

}

public void DatabaseCode(string arg) {

           .... code here ...

}

Be improved in code B :

static void Main(string[] args) {

           DatabaseCodeDelegate slave = DatabaseCode;
           slave ("test");

}

public void DatabaseCode(string arg) {

           .... code here ...

}
public delegate void DatabaseCodeDelegate(string arg);

It seems that this is subjective, but an area where there are strong conflicting view points?

Answer 2

I primarily use the for easy asynch programming. Kicking off a method using a delegates Begin... method is really easy if you want to fire and forget.

A delegate can also be used like an interface when interfaces are not available. E.g. calling methods from COM classes, external .Net classes etc.

Answer 3

The .NET 1.0 delegates:

this.myButton.Click += new EventHandler(this.MyMethod);

The .NET 2.0 delegates:

this.myOtherButton.Click += delegate {
    var res = PerformSomeAction();
    if(res > 5)
        PerformSomeOtherAction();
};

They seem pretty useful. How about:

new Thread(new ThreadStart(delegate {
    // do some worker-thread processing
})).Start();

Answer 4

One of the benefits of Delegates is in asynchronous execution.

when you call a method asynchronously you do not know when it will finish executing, so you need to pass a delegate to that method that point to another method that will be called when the first method has completed execution. In the second method you can write some code that inform you the execution has completed.

Answer 5

For example in multithread apps. If you want several threads to use some control, You shoul use delegates. Sorry, the code is in VisualBasic.

First you declare a delegate

Private Delegate Sub ButtonInvoke(ByVal enabled As Boolean)

Write a function to enable/disable button from several threads

Private Sub enable_button(ByVal enabled As Boolean)
    If Me.ButtonConnect.InvokeRequired Then

        Dim del As New ButtonInvoke(AddressOf enable_button)
        Me.ButtonConnect.Invoke(del, New Object() {enabled})
    Else
        ButtonConnect.Enabled = enabled
    End If

End Sub

Answer 6

there isn't really anything delgates will solve that can't be solved with other methods, but they provide a more elegant solution.

With delegates, any function can be used as long as it has the required parameters.

The alternative is often to use a kind of custom built event system in the program, creating extra work and more areas for bugs to creep in