Question

I am working on a UserControl for selecting special files, in this control there is a TreeView which gets populated with nodes when user selects some file. Also user can remove the files from this treeview!

I am using this control in a wizard form. In this wizard form there is a button named buttonNext and this button is disabled by default.

How can I create an event for the treeview in the usercontrol that when it gets populated it notify the next button in wizard form to get enabled and if user removes all files from that treeview it notify the button to get disabled again.

P.S: Selecting files (browser dialog and stuff like that) are all done within this usercontrol, so in my wizard form I have no access to the things that is going on in this component, but only I set the TreeView itself as public so I can read its nodes in my wizard form.

I know how to subscribe to events but never created any event myself 🙁

Answer 1

Declare events on your CustomControl:

public event EventHandler DataPopulated;
public event EventHandler DataRemoved;

Common practice is creating protected virtual methods (for possible overriding them in descendant classes), named On<EventName> which will verify that event has attached handlers and raise event, passing required arguments:

protected virtual void OnDataPopulated()
{
    if (DataPopulated != null)
        DataPopulated(this, EventArgs.Empty);
}

NOTE: If you need to pass some data to event handlers, then use generic EventHandler<DataPopulatedEventArgs> delegate as event type, where DataPopulatedEventArgs is a class, inherited from EventArgs.

Then just call this method just after your data was populated:

treeView.Nodes = GetNodes();
OnDataPopulated();

Then just subscribe to this event and enable your next button:

private void CustomControl_DataPopulated(object sender, EventArgs e)
{
   buttonNext.Enabled = true;
}