deliciouslytyped/andrexpmt

andrexpmt's Issues

Drag and drop bug

To run the app just press the play button in intellij.
Im using the android 30 image in the emulator, but the jetpack compose preview feature also exhibits the below behaviour, you just cant run the debugger against that IIUC.

The drag and drop code is from

andrexpmt/comp/src/main/java/com/example/comp/dnd/author

Lines 1 to 4 in f775839

	https://www.youtube.com/watch?v=ST99k8qK6SM
	(Android Drag and Drop in Jetpack Compose (with Animation) - Android Studio Tutorial with Kotlin)
	(K Apps, Matthias Kerat, 2022)
	https://github.com/MatthiasKerat/DragAndDropYT/tree/main

Problem description

Hi folks, I'm doing a homework project in jetpack compose and I have a bug I havent been able to track down after hours of debugging. I only have a basic knowledge of jetpack; the issue is that I'm either getting some stale, or refreshed data in a lambda closure in a composable, I cant tell.

i.e. dataToDrop is wrong in this scope, but everywhere else I've managed to look in the debugger, at any given time the data seems to be correct (except when this code runs):

andrexpmt/comp/src/main/java/com/example/comp/dnd/DragAndDrop.kt

Lines 74 to 79 in f775839

	detectDragGestures(onDragStart = {
	viewModel.startDragging()
	currentState.dataToDrop = dataToDrop
	currentState.isDragging = true
	currentState.dragPosition = currentPosition + it
	currentState.draggableComposable = content

It's passed here:

andrexpmt/comp/src/main/java/com/example/comp/dnd/DragAndDrop.kt

Line 59 in f775839

dataToDrop: T,

and I would hope it is a constant reference to the appropriate LetterTileModel object.

I'm trying to drag and drop some tiles onto a game grid, and the drag operation passes a tile model object around, I have a "list" of tiles the user can drag from, and that works fine-ish; when I take a tile out of the list and put it on the grid, the remaining tiles get relabeled just fine, however somehow the stored drop data (the internal identity of the tile) somehow retains the original ordering, and I find this completely incomprehensible.

So if my tiles are [ H Y D P E ] and I take out H and put it on the grid, the remaining tiles show as [ Y D P E ] but their identities are [ H Y D P ], or at least debugging shows that when picking up the remaining tile, the onDrag data will have the labels H Y D P respectively. Placing the Y tile will result in a crash because the "owner" of the H tile is now a TileSocket which doesnt implement move(), and move() is called on the owner.

(This results in various odd behaviors such as the fact that placing every other tile will work (presumably because the incrementing off-by-one issue will not have assigned an already placed identity to the tile yet))

The specific issue is that the dataToDrop argument passed through DropTarget to the onDrag callback is the wrong offset list data (but I don't understand how it can end up like that)

The game crashes when placing a tile located after a previously placed tile because the "owner" of the previous tile is now a socket, which doesn't implement move() and throws a TODO() exception, but the actual problem is that the identity of the second tile refers to the first tile's identity, and not that the exception happens

Sidestepping the exception results in placing the identity of the first tile any number of times
(because its not removing the new tile from the playable tile set)

(I don't understand how the displaying list can be correct, but the identities can be offset, when Im not doing any sort of mutation on which tile has which identity, and I don't even have a data structure that manages that as an aggregate, its assigned to tiles individually...I think.)