ListView does not show on phone


I want to show a List of Details, from a Master-Detail Relation. The Master is the Customer (Kunde) and the Detail should be Test. I implemented the method in my code and the code works perfectly fine. I am able to choose a Customer by ID and the List of tests that belong to the Customer pops up.

In this image i implemented a TinyDB to store the value of the Customer ID, of which list of tests I want to show.
The TinyDB is called in the first image. But for some reason the ListView never shows the list.

What could possibly be the problem? It seems that I never get to use the TinyDB...

What is your url for the GET here:


How can a text box .text value be changed before a screen initialize runs?