How to make a message pop up

Hey, im making a program for a school project where i have to make a shopping list using a text box to add to a list that keeps on continuing, and can use a list picker to delete items when i want to, my question is can i make it so an error message of some kind pops up if you try to delete using the list picker but there are no items listed yet?

Use logic and the notifier

Do you think you could give me an example/show me how to use it? I’m not that great at App Inventor yet, here is my code if it helps

Something like this:


Actually, you need to use a button to run the condition test (as opposed to the listpicker button) otherwise the listpicker - empty or not - will still be displayed.

You can untick the visibility of the listpicker but it will still work.


I have misunderstood what was required of me, i dont have to have an error message if there’s nothing to do delete, which brings me to my next question, is there a way to have a message pop up when there is nothing in the list? I’ll be switching between screens if i need to set it when the screen changes by a button.

Then place that list condition check in the button you press to switch screens.

Some advice on screens (although it may be a requirement of your project to actually use more than one screen?)

Use different screens wisely

If you decided to use different screens, then you should switch them correctly, else you will run out of memory after a while...      
The recommended method of switching screens in App Inventor
(Thanks Taifun)
Also see demo: multiscreen.aia


How the project is supposed to work is when you press the buttons to switch lists (there are 4 of them) the background changes and the list for each store pops up, i havent really had any success in doing this other than changing screens back and forth.

This might be just what you want ?!category-topic/mitappinventortest/K-zAr2X3nio

You could have a list viewable on each “screen” - use the listview as opposed to the listpicker

this should work, thanks, would i have to make a new text box to add to the list on each screen? or would the one work for each?

If only using one screen (so you are using “virtual screens”) then you could use one textbox, but you would need a way of identifying which list you want to add the content to (perhaps a different button for each list?)

If using multiple screens, then it is easier to have a textbox on each screen for data entry

Im using virtual screens, could i make it somehow so buttons overlap but dissapear when i change virtual screens? so it looks like its the same button but changing?

Not sure i fully understand what you mean?

You could have previous and next buttons ?

I mean is there somehow i could have different buttons to add to the different lists, but make it so when i change screens you can only see one of the add buttons at a time (that corresponds to the virtual screen)

Put that button in the virtual screen, so that it only shows when the virtual screen is displayed ?

In my tabbed screens demo app, I have a label in each screen as an identifier…