How to diable "Next" button when MUI textbox have nothing?

I tried to MUI Next button set disable when textbox don't have anything(check Next button state at every key input changed), but it's difficult for me ... how is that possible?

( I am sorry I cannot write english well...🙁 )

If you use nsDialogs to create the custom page, you can use the onChange function to go to an NSIS function every time something is changed in the textbox. In that function, simply get the text out of the textbox and compare it with "".

Littlepot, You could use something like this:

${If} $variable == ""
GetDlgItem $6 $HWNDPARENT 1   
EnableWindow $6 0 ; disable 
${Else}
GetDlgItem $6 $HWNDPARENT 1   
EnableWindow $6 1 ; enable
${EndIf}