Recognizing sender button control in click event

You need to cast to the type of your custom class that has the Data field.

Something like:

YourCustomButton button = sender as YourCustomButton;

Assuming your custom button type is CustomButton, you should do this instead:

CustomButton_Click(object sender, EventArgs e){
  CustomButton button = sender as CustomButton;
  if (button != null){
      // Use your button here
  } 
}

If you dont want to set a variable the simple way to do is:

((CustomButton)sender).Click

or whatever you want.