Removing an EventHandler (ComboBox)

[Salte2]

There is a ComboBox on my Windows Form. I have two different methods that are called when the Form is made visible, depending on what action the user intends to perform. In one case, i want the ComboBox to be tied to an EventHandler, and in the other case, i dont want it to be. So how can i make sure that the EventHandler is not triggered? Here are the two methods in question:

public void ShowFormWithEHandler()
{
cbx.SelectedIndexChanged += new EventHandler(TypeValgt);
ShowDialog();
}

public void ShowFormWithoutEHandler()
{
<?????>
ShowDialog();
}

What do i put where the ????? are now (to remove the eventhandler that might have been added previously)? And will the "+=" in the first method give me problems (it might be executed several times).

 

[dalchri]

1) If you truely do not want the event fired, I would track this in the VisibleChanged event and use a module level boolean to track the status.

//This is at the module level
private bool m_blnShowFormWithEHandler = true;

private void Form_VisibleChanged(EventArgs evt) {
//Do not deal with the event handler at all
//unless the flag is set
if (m_blnShowFormWithEHandler) {
   if (this.Visible) {
      //Enable the event handler when the form is shown
      cbx.SelectedIndexChanged += new EventHandler(TypeValgt);
   } else {
      //Remove the event handler after the form is hidden
      //because the event will fire multiple times if it
      //is added several times without being removed
      cbx.SelectedIndexChanged -= new EventHandler(TypeValgt);
}

public void ShowFormWithEHandler()
{
m_blnShowFormWithEHandler = true;
ShowDialog();
}

public void ShowFormWithoutEHandler()
{
m_blnShowFormWithEHandler = false;
ShowDialog();
}

2) The easier and less risky approach would be to always fire the event but use a module level boolean to ignore or enable the event.

//This is at the module level
private bool m_blnShowFormWithEHandler = true;

private void cbx_SelectedIndexChanged(EventArgs evt) {
if (m_blnShowFormWithHandler) {
   //Do stuff here
}
}

public void ShowFormWithEHandler()
{
m_blnShowFormWithEHandler = true;
ShowDialog();
}

public void ShowFormWithoutEHandler()
{
m_blnShowFormWithEHandler = false;
ShowDialog();
}

 

[Salte2]

Thank you very much dalchri. That is very helpful.