How do you transfer an item in a list to another list without replacing the old data in the new list from another screen?

MIT App Inventor Help
#1

Hi everyone, basically I am trying to create a book reservation system. In the main page, the user will be able to click on a book from a list and the book info will then be transferred to another list called the reservationlist in another screen. So far I am able to transfer 1 data to the other screen but whenever I tried to go back to the 1st screen and I tried to send another data to the other list, it will replace the previous data in the list. I suspect the problem lies in the start value that I send to the other screen but I'm not so sure about this. Here are the sample of the coding blocks of screen 1 and 2.

Screenshot 2023-07-06 221630
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Screenshot 2023-07-06 221748
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Anyone know how to solve this? English is not my first language so I am sorry if there's any mistake.

#2

You need three tables for this:

  • books in your collection
    • unique book ID (for multiple copies)
    • book Title
  • people who can borrow books
    • unique person ID (email address?)
    • person name
  • book reservations
    • unique book ID (from book collection)
    • list of reservations, oldest first
      • unique person ID
      • date contacted of availability

Do not use ListViews as data storage.
Refresh the ListView Elements as needed from TinyDB NameSpaces and sorted and filtered lists.

#3

So I need to create another data storage to store the chosen item from the list? If so, whenever I use the block listView afterpicking, store data to book reservation. Then on the 2nd screen, I just initialize the list to display the data from the book reservation table?

#4

Also, it is a good idea to use multiple stacked Vertical Arrangements, only one visible at a time, instead of Screens, to avoid problems transfering data scross Screens.

Use Media Files to store your starting book collection and borrower list, as .csv files.
At Screen Initialize, look in TinyDB to see if you have already loaded those files into TinyDB. otherwise issue File Reads for those Files.

Do not try to keep your collection in text blocks. It would overwhelm the Blocks Editor and Build processors.

#5

Thank you for the suggestion, I will try it first and update any progress soon.

#6

Since I am still new to mit app inventor, I am still not used to using media files and csv files as a storage. I am currently approaching this problem with another method.

Screenshot 2023-07-06 234616
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How about using this method? I have tried it but still it just replaced the old data with the new data. It would be nice if I can just keep going back to add data without worrying to replace the old data in the new list.

#7

You also need to learn to use lists and tables for this project.

See the introductory section of

and do not keep lists as text, to preserve item boundaries.

#8

Alright, I'll get through the files first.

#9

I have gone through the files but I don't know how to implement it to my project. Any ideas or blocks that I can use to implement it with my project?

#10

Here is a sample project showing how to enter and store complex data into TinyDB...

#11

Thank you. I will refer to the project first.

#12

Hi, I have referred to the project and make some changes to my app but it still would not add a new data to the list and replace the old data with the new one. I have changed back the blocks to my original blocks. May I share my aia file here and may I ask you to point out what I need to change and how to do it?

#13

(Canned Reply: ABG- Export & Upload .aia)
Export your .aia file and upload it here.
export_and_upload_aia

#14

Thank you, here is my aia file.
ArchiveMaster.aia (1.2 MB)

#15

Hi, any updates regarding my app?