how to contrl the state of "next" botton according to the text box?

i create a custompage to get some message frome the textbox,
so i want the "next" botton of the page is disable,when i get no string from the textbox?
how to do this?

And refuse to receive Space character?

You can't have the next button disabled, but you can check the text in the leave function of the page and call Abort if it isn't right.

That just is what i done!

just set "MinLen=1" in the [Field X] section of your textbox in your custompage ini file