Nut_Sort (1).aia (475.5 KB)
I am building a Ball/Nut Sort puzzle game in MIT App Inventor using lists of lists (each rod is a list, stored inside a global rods list).
Each move should:
Take the top item (last item) from fromRod
Add it to the end of toRod
Only allow the move if:
toRod is not full
AND (toRod is empty OR top color of toRod equals moving color)
The problem
Even though I select a green nut from rod 2 and move it to rod 3:
The nut arrives as a different color (e.g. red)
At the same time, other rods change colors automatically
Sometimes two items appear in the destination rod after one move
It looks like colors are being swapped or corrupted, even though I never change colors directly.
What I have already tried
Using copy list for fromList and toList
Ensuring remove/add only happens inside if canMove = true
Making sure only one place in the code modifies the lists
Fixing insert index errors (length + 1)
Fixing color comparison logic (topTo = movingColor)
Rendering images only from the list values
My current move logic (simplified)
fromList = copy of rods[fromRod]
toList = copy of rods[toRod]
movingColor = last item of fromList
if toList is full → canMove = false
else if toList is empty → canMove = true
else if topTo = movingColor → canMove = true
else → canMove = false
if canMove:
remove last item from fromList
insert movingColor at end of toList
replace rods[fromRod] = fromList
replace rods[toRod] = toList
Render()
Expected behavior
Only the selected nut moves
Colors remain consistent
Other rods are not affected
Actual behavior
Colors randomly change
Other rods get modified
Destination rod sometimes gets duplicate items
Question
Is this caused by:
List reference issues in App Inventor?
insert list item behavior?
Rendering logic?
Something else I am missing?
Any guidance or example of a stable list-of-lists move pattern in App Inventor would be greatly appreciated.
It is similar (but not equal to) the Towers of Hanoi puzzle, with three fixed height rods representing limited height stacks, and different legality constraints.
For list manipulation of stacks, you would typically use two list blocks:
add item to list (if stacked vertically like the video) and
remove item (length of list) from list
If stacked in the other direction, you would use
insert at item 1
remove item 1
I'm going back into your code, to see how it works, but if it was me, I would got for a value function based approach, where you avoid doing in-place manipulation of lists, but instead pass around freshly built altered copies of the data structures.
to see which way the rod (bolt) faces, to see how that constrains the stacking.
I can't envision how you could combine these images to show a bolt sticking through a series of nuts.
You might fix them by pasting sections of bolt shaft over their top parts, since the nuts themselves won't appear away from a bolt anyway. The none image would just be a section of bolt shaft, not empty space.
Setting target nut slot buttons as enabled or disabled is a needless aggravation.
Testing your app, I got stuck with no enabled buttons in my target bolt:
