WinForms: How to programatically fire an event handler?

Question

i want to programatically invoke an event handler for a control. For example:

DateTimePicker dtpLastConsummated;

i want to trigger the TextChanged event handler for the dtpLastConsummated, how can i do it?

In other languages i would call something akin to:

dtpLastConsummated.TextChanged(this, new EventArgs());

but in .NET you can have multiple event handlers:

dtpLastConsummated.Click +=new EventHandler(dtpLastConsummated_TextChanged);
dtpLastConsummated.Click +=new EventHandler(dtpLastConsummated_AnotherHandler);
dtpLastConsummated.Click +=new EventHandler(dtpLastConsummated_MoreHandlers);
...
dtpLastConsummated.Click +=new EventHandler(dtpLastConsummated_Nminus1);

so you need a way to trigger all the attached event handlers.

---

Answer

The following code will fire the event:

Toolkit.FireEvent(dtpLastConsummated, "TextChanged", new EventArgs());

And here's the code of the static toolkit function:

/// <summary>
/// Programatically fire an event handler of an object
/// </summary>
/// <param name="targetObject"></param>
/// <param name="eventName"></param>
/// <param name="e"></param>
public static void FireEvent(Object targetObject, string eventName, EventArgs e)
{
   /*
    * By convention event handlers are internally called by a protected
    * method called OnEventName
    * e.g.
    *     public event TextChanged
    * is triggered by
    *     protected void OnTextChanged
    * 
    * If the object didn't create an OnXxxx protected method,
    * then you're screwed. But your alternative was over override
    * the method and call it - so you'd be screwed the other way too.
    */

   //Event thrower method name //e.g. OnTextChanged
   String methodName = "On" + eventName;

   MethodInfo mi = targetObject.GetType().GetMethod(
         methodName, 
         BindingFlags.Instance | BindingFlags.NonPublic);

   if (mi == null)
      throw new ArgumentException("Cannot find event thrower named "+methodName);

   mi.Invoke(targetObject, new object[] { e });
}

---

Note: i'm not creating a subclass of every control in the .NET framework, and every 3rd party control, and convincing an enterprise worth of developers to retrofit every form to use my custom controls.

Answer 1

Button in Windows Forms is a special case, because it has a PerformClick method to do exactly what you're talking about. For other events in other controls, though, there's really nothing similar.

Answer 2

You can inherit from that class and create a new method that calls the protected OnSomeEvent() method.

class MyButton : Button
{
    public void CauseClick()
    {
        this.OnClick();
    }
}

As Matt pointed out, you can use PerformClick() for this specific example. However, most events don't have corresponding public functions to trigger them.

Answer 3

3 suggestions to fire the TextChanged Event:

Manually change the text:

        string s = dateTimePicker1.Text;
        dateTimePicker1.Text = String.Empty;
        dateTimePicker1.Text = s;

or

Inherit from DateTimePicker and create a new method that exposes / calls DateTimePicker's protected OnTextChanged

public class MyDateTimePicker : DateTimePicker
{
    public void OnTextChanged(EventArgs e)
    {
        base.OnTextChanged(e);
    }
}

or

If you don't like OOP and want to break encapsulation, you can access the protected OnTextChanged method through reflection:

        MethodInfo onTextChanged = dateTimePicker1.GetType().GetMethod("OnTextChanged", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance);
        onTextChanged.Invoke(dateTimePicker1, new object[] { new EventArgs() });