Text.change

Is there a way to work with numbers in a textbox as the text changes? I have a app I am trying to build & I want to do math with the numbers entered in a few text boxes but I don't want to have to click a button to calculate it. I would like it to work as the text is changed. I can use get or lost focus but then I need something like on error resume next so it wont error if there is blank text.
 Just wondering

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Test before calculating with the is a number Math block.

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but I don't want to have to click a button to calculate it.

use a cock component to do the calculation 

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 I figured out the is a number block it works the same as If isnumeric in vb. But trying to get my math equations into the blocks is kicking my but. 

This is what I am trying to do but not sure yet if I can with this?

        Tf = TextBox1.Text

        RH = TextBox2.Text

        P = TextBox3.Text

        P = P * 33.863867

        TC = (Tf - 32) * (5 / 9)

        tk = TC + 273.16

        Es = 6.11 * 10.0# ^ (7.5 * TC / (237.7 + TC))

        E1 = RH * Es / 100

        Tv = tk / (1 - (E1 / P) * (1 - 0.622))

        Tv = Tv - 273.16

        Tv = (9 / 5) * Tv + 32

        Tv = Tv + 460

        psta = P / 33.863867

        x = (17.326 * psta) / Tv

        Da = 145366 * (1 - (x ^ 0.235))

        dap = psta - E1

        z = 1 - (0.01 * RH)

        TextBox5.Text = Math.Round(Da, 2)

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just do it... step by step... see also http://stackoverflow.com/a/26041125/1545993

and

Top 5 Tips: How to learn App Inventor

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Wow. Thanks Taifun. That was a big help. One more question and I will try to stop bugging you and get this figured out. Is there a way to make temporary fields like TC, TK, ect or will have to add hidden fields to hold them? For example is there a way to say Dim TC as single and then TC = 100 and then use TC in my math or will I have to add a hidden label or something to hold TC ?  

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Is there a way to make temporary fields like TC, TK, ect or will have to add hidden fields to hold them? 

what about using variables?

A very good way to learn App Inventor is to read the free Inventor's Manual here in the AI2 free online eBook   http://www.appinventor.org/book2 ... the links are at the bottom of the Web page.  The book 'teaches' users how to program with AI2 blocks.

There is a free programming course here http://www.appinventor.org/content/CourseInABox/Intro  and the aia files for the projects in the book are here:  http://www.appinventor.org/bookFiles  

How to do a lot of basic things with App Inventor are described here:  http://www.appinventor.org/content/howDoYou/eventHandling  .

Also do the tutorials http://appinventor.mit.edu/explore/ai2/tutorials.html to learn the basics of AppInventor, then try something and follow the

 Top 5 Tips: How to learn App Inventor

You will not find a tutorial, which does exactly what you are looking for. But doing the tutorials (not only reading a little bit) help you to understand, how things are working. This is important and this is the first step to do.

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Look in particular for local variables.

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