Run a code when form is activated

Hi,

I want to run a code when the form is activaed. I added MessageBox.Show("HELLO") in the activated event and then opened the form, then I opened some Form as dialog but when I close I was expecting to get the Message HELLO but I didn't get it.

So what's the best way to run a code when the fom is activated or brought to front?

Thanks

Jassim