You can use the feedback app as a start. I never worked with PostGRESQL, but if B4J can do it, so can you using ABMaterial. Remember, ABMaterial is just for making the pretty UI, al the rest is done in pure B4J.
You have to first grab the component (see the demo apps). You must get all its parents too to get to the component (e.g. if the parent is a container, you first have to get the container and then the component from that container)
Example for a component added to a page:
B4X:
Dim myInput AS ABMInput = page.component("myInput")
dim variable as String = myInput.Text
For a table, it is slightly different (untested code as I'm not on my PC right now):
B4X:
Dim myTable as ABMTable = page.Component("myTable")
Dim myInput as ABMInput
for i = 0 to 10
myInput = myTable.GetComponent(i, "myInput")
dim variable as String = myInput.Text
next