KeyUp - triggering twice

Question

had the issue that my KeyUp and the KeyDown Event both fired twice when i invoked them. Finally found a fix for this:

  this.glControl1.KeyUp -= this.glControl1_KeyUp;
  this.glControl1.KeyUp += new KeyEventHandler(this.glControl1_KeyUp);

It works, but i really cant understand why. Could anyone explain me please.

Thank you

Answer 1

You probably have some repetitive event which you use as a trigger to hook up your event handler, a classic example is a button click e.g.

public void ButtonClick(object sender, EventArgs e)
{
    this.SomeControl.KeyUp += this.SomeHandler;
}

The problem here is everytime the button is clicked the same event handler is assigned to the same event, there is nothing to prevent this from happening as it can be perfectly acceptable under certain circumstances.

To avoid this, you need to unhook the event handler before you reassign it, this is why executing the following line of code

this.SomeControl.KeyUp -= this.SomeHandler;

Before you assign the event handler prevents duplicate calls.