Dynamic event subscribe and unsubscribe to a C# event

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How to dynamically subscribe and unsubscribe to a C# event in windows Forms Application. so that given a Object instance and a String name containing the name of the event, you subscribe to that event and do something when that event has been fired?

What I have tried:

string _EventHandler = string.Empty;

_EventHandler = cntrl + @"." + _EventName;

_EventHandler += new EventHandler(SaveData);

private void SaveData(object sender, EventArgs e)
{
// doing something
}

Posted 25-Feb-18 22:16pm

Poornima Santhosh

Updated 27-Feb-18 20:02pm

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Comments

Richard MacCutchan 26-Feb-18 4:30am

You need to use reflection to find the actual event reference from the string.

2 solutions

Solution 2

Hi I got the solution here is my code

// Code for subscribing an event to call other class method
// code for adding a method in another class to the control event
// here _EventName is the name of the event (Click, Enter, Leave etc..)
// In MyEventsHandler class I have a SaveData method

EventHandler eHandler = new EventHandler(MyEventsHandler.SaveData);
AddHandler(cntrl, _EventName, eHandler);

//Function to add Eventhandler
private void AddHandler(Control c, string eventName, EventHandler handler)
{
try
{
Type t = c.GetType();
EventInfo ei = t.GetEvent(eventName);
ei.RemoveEventHandler(c, handler);
ei.AddEventHandler(c, handler);
}
catch (Exception ex)
{
MessageBox.Show(System.Reflection.MethodInfo.GetCurrentMethod().Name + " " + ex.Message,
"Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
}
}

Posted 27-Feb-18 20:02pm

Poornima Santhosh

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

OriginalGriff · Accepted Answer · 2018-02-26T01:21:00

Solution 1

Not too difficult ... just messy, because you need to play around. Try this:

private void AddHandler(Control c, string eventName, EventHandler handler)
    {
    Type t = c.GetType();
    EventInfo ei = t.GetEvent(eventName);
    ei.AddEventHandler(c, handler);
    }

But I hope you have a good reason, because it's not going to improve your code readability...

Posted 26-Feb-18 1:21am

OriginalGriff

Comments

Poornima Santhosh 27-Feb-18 0:00am

Thank you I have tried this Its working if I have a method in the same class.

if I have a SaveData method in another class. how can i add it to the eventhandler?

OriginalGriff 27-Feb-18 3:11am

Unless the event is part of the class to which it is being subscribed, you can't attach it - events don't work like that.
In order for an event handler to be called, the class that created the event has to very specifically run code to execute it:
https://www.codeproject.com/Articles/400287/A-simple-code-snippet-to-add-an-event
Shows the code you need to use in your class in order to get a handler to run.
Unless a class has the event to start with, that code would not be run, and the handler would never execute.
You can't attach a handler to an event the class doesn't expose: it doesn't exist and the handler would not be called if you could attach it!

Dynamic event subscribe and unsubscribe to a C# event

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Dynamic event subscribe and unsubscribe to a C# event

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