CODEWITHSUNDEEP
c#.netvb.net
anaval
anaval

Reputation: 1138

c# creating events without delegates like VB.net

My Code in VB.net

Public Class Form1
    'step 1. declare the event
    Private Event TestEvent(ByVal msg As String)

    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        'step 2. raise the event
        RaiseEvent TestEvent("Hello World")
    End Sub

Private Sub Form1_load()
    'step 3. add the event handler
    AddHandler Me.TestEvent, AddressOf test_handler
Sub

Private Sub test_handler(ByVal message As String)
    MsgBox(message)
End Sub
End Class

My Code in C#

namespace CSharp_Event_Test
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        //step 1. declare delegate of event
        private delegate void TestEventHandler(string msg);
        //step 2. declare the event
        private event TestEventHandler ActualTestEvent;

        private void button1_Click(object sender, EventArgs e)
        {
            //step 3. raise the event
            ActualTestEvent("Hello World");
        }
        private void Form1_Load(object sender, EventArgs e)
        {
            //step 4. Specify the event handler
            this.ActualTestEvent += new TestEventHandler(test_event);
        }

        private  void test_event(string M) {
            MessageBox.Show(text: M, caption: "Event Raised");
        }
    }
}

Both of them work actually. Im just curious why I was able to declare an event in VB even without a delegate but in C# making events without delegate gives me an error.

Upvotes: 1

Views: 1094

Answers (2)

Adam
Adam

Reputation: 1885

See also C# event with custom arguments

class Program
{
    public static event Action<string> myEvent;

    static void Main(string[] args)
    {
        myEvent += Program_myEvent1;
        myEvent("Cheese");
    }

    private static void Program_myEvent1(string val)
    {
        Console.WriteLine(val);
        Console.ReadKey();
    }
}

The trick is to use Action<T> instead of EventHandler

Upvotes: 3

sstan
sstan

Reputation: 36483

Q: I'm just curious why I was able to declare an event in VB even without a delegate but in C# making events without delegate gives me an error.

As explained in this article on delegates, it's because VB.NET is capable of implicitly declaring a delegate type for you when declaring an event:

Although you can create your own delegates, in most cases Visual Basic creates the delegate and takes care of the details for you. For example, an Event statement implicitly defines a delegate class named <EventName>EventHandler as a nested class of the class containing the Event statement, and with the same signature as the event.

Unfortunately, C# doesn't provide this convenient syntactic sugar, so you have to explicitly declare the delegate type before declaring the event. (Or, as observed in Adam's answer, you can reuse existing delegate types)

Upvotes: 7

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