[BUG] [CancellableNetworkTileProvider] Exception: Buffer parameter must not be null

[lonelyteapot]

What is the bug?

I use CancellableNetworkTileProvider from the plugin. Frequently, when requests are cancelled, an unhandled Exception: Buffer parameter must not be null is shown in the console.

I haven't found where this exception comes from, but I think I've found the root cause:

_CNTPImageProvider uses an ImmutableBuffer that has been disposed:

https://github.com/fleaflet/flutter_map_cancellable_tile_provider/blob/dac6a1dddab0bdfda34049331ff6c2aee3379c64/lib/flutter_map_cancellable_tile_provider.dart#L147

Here, an ImmutableBuffer is created from TileProvider.transparentImage once, and then cached in tileProvider._cancelledImage for the whole lifetime of the TileProvider.

However, during the decode call, this buffer is disposed by sky_engine:

https://github.com/flutter/engine/blob/d379d53b8ab1f53244cce9fc6e9918bbdd18ecd6/lib/ui/painting.dart#L2317

How can we reproduce it?

https://github.com/fleaflet/flutter_map/blob/master/example/lib/pages/cancellable_tile_provider.dart

Do you have a potential solution?

Replacing ??= with ?? in the line linked above (therefore creating a new ImmutableBuffer on each cancelled request) seems to resolve the issue.

Platforms

Android 12 (Samsung Galaxy M21)

Severity

Minimum: Allows normal functioning

[JaffaKetchup]

Thanks for reporting. I can't remember getting this issue myself, but I guess it makes sense that it would occur.

We'll look into this along with the other issues from v6.

[JaffaKetchup]

Fixed in the latest 'main' on the plugin repo.

[tijee]

Hi @JaffaKetchup thank you for the fix. Do you have an ETA for the next release?

[JaffaKetchup]

We may be able to release a version for the plugin before the main repo. No planned date yet though.