how do i check or validate data in app inventor?

[ali jafari]

I would like to have validation key properties in my application .for example i need to force user to enter numerical data in textbox and show some special message to user when they dont enter numerical. data. I really appreciate if someone help me.

[Hal Abelson]

If you are wondering about general validation, then you need to examine the input when it is done and write a program to examine the input and decide if it's OK.

If you are asking specifically about making sure that the input is a number, then set the NumbersOnly property of the text box.