UserControl custom event

Question

1.00/5 (1 vote)

See more:

Hello,
i am creating a custom ComboBox UserControl formed out of a button, a textbox and a panel. I got to the point where i add the events of the control, and i got stuck. Particularly, SelectedIndexChanged event. I don't know how to add this event to my control. I tried:

VB

Public Shadows Event SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs)

AddHandler MyBase.SelectedIndexChanged, AddressOf _Combobox_SelectedIndexChanged

Private Sub _Combobox_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles MyBase.SelectedIndexChanged
        RaiseEvent SelectedIndexChanged(sender, e)
End Sub

but its obviously not the right way... Here is what i get:

Event 'SelectedIndexChanged' cannot be found. - for the Sub

'SelectedIndexChanged' is not an event of 'System.Windows.Forms.UserControl'. - for the second line of code...

What am I doing wrong? Also, I might have set the control to inherit Combobox and inherit its events, properties and methods, but for a specific reason I need it to inherit UserControl.
Thank you!

Posted 15-May-13 5:52am

rusoaica_

Add a Solution

Comments

Yuriy Loginov 15-May-13 12:27pm

try this link: http://msdn.microsoft.com/en-us/library/ms973905.aspx

Sergey Alexandrovich Kryukov 15-May-13 12:30pm

Not exactly the right MSDN page. OP needs to know declaration of event instances, the class members.
—SA

Yuriy Loginov 15-May-13 12:41pm

fair enough, what I forgot to mention is that when creating a custom control you need to create custom events as well. In this case you want to declare

Public Event SelectedIndexChanged(ByVal sender As Object, ByVal e AS EventArgs)

and then raise the event

RaiseEvent SelectedIndexChanged(this, e)

You most likely will want to raise the event in response to the SelectedIndexChanged of the child DropDown contained in the custom control.

Sergey Alexandrovich Kryukov 15-May-13 12:47pm

I provided a very detailed answer, please see.
—SA

1 solution

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Sergey Alexandrovich Kryukov · Accepted Answer · 2013-05-15T06:45:00

This is simple. Your only problem is that you seemingly know how to use the already declared events, handle them. It means, you know the usage without understanding of events, otherwise you would know how to declare and invoke then. You try to act like a user of the class declaring an even, while you need to act like an author of such class.

All you need to know is: 1) declaration of an event instance as a member of class/structure (control class, in your case), 2) event invocation. Those are two items you never could do as a mere user of some class/structure. Not that the invocation of the event is only possible from its declaring class, impossible even from the derived class. (Many asked how to fire some certain event. It makes no sense at all. If event is already declared in a library, it cannot be invoked elsewhere: this limitation is the important fool-proof feature.)

You just need to start over about learning the events and perhaps delegates. Please start here: http://msdn.microsoft.com/en-us/library/awbftdfh.aspx[^].

The general patten is simple. First, you need to have some event argument class. Use one of available classes or derive your own one from System.EventArgs class, which is only needed when you have to pass your custom parameters to a handler of an event.

C#

class MyEventArgs : System.EventArgs {/* ... */}

VB.NET

Class MyEventArgs
	Inherits System.EventArgs
	' ... 
End Class

Then, declare the control class:

C#

public class MyControl : Control {

   public event System.EventHandler<MyEventArgs> MyEvent;
   // no initialization ever needed, it cannot be initialized
   public event System.EventHandler MySimlestEvent;

   // and here is the way to invoke events:

   void InvokeMyEvent() {
      if (MyEvent != null) 
          MyEvent.Invoke(this, new MyEventArgs(/* this is how arguments are passed to the handler */));
   }

   void InvokeMySimplestEvent() {
   if (MySimplestEvent != null)
       MySimplestEvent.Invoke(this, new System.EventArgs()); // no arguments
   }

   // in case of user control, use the above two methods in the pre-set event handlers of children

}