Broken Map Tiles cached?

[codeOfJannik]

Hi @JaffaKetchup and thanks again for the great package!

We've encountered an issue where, under certain conditions like poor internet connection, high network load, or heavy memory usage, map tiles fail to load correctly and appear grey. Strangely, these grey tiles persist even after the app process is killed and restarted under stable conditions.

This seems to suggest that tiles that failed to download properly are being cached and then treated as valid on future launches, preventing the app from retrying to fetch the correct tiles.

Is there any mechanism in the package that could explain this behavior? Are failed tile fetches (e.g., due to timeouts or incomplete responses) ever written to the cache as if they were successful?

Thanks in advance!

[JaffaKetchup]

Hi @codeOfJannik,
Sorry about this. I'm very busy for the next couple weeks so not much time to look into things immediately.

But in the meantime, FMTC should be attempting to decode the tile before storing it:

flutter_map_tile_caching/lib/src/providers/image_provider/internal_tile_browser.dart

Lines 167 to 183 in 022bbe0

	try {
	isValidImageData = (await (await instantiateImageCodec(
	response.bodyBytes,
	targetWidth: 8,
	targetHeight: 8,
	))
	.getNextFrame())
	.image
	.width >
	0
	? null
	: Exception('Image was decodable, but had a width of 0');
	// We don't care about the exact error
	// ignore: avoid_catches_without_on_clauses
	} catch (e) {
	isValidImageData = e;
	}

So I'm surprised it's grey. Here's a couple suggestions for debugging:

• If you can find the tile coordinates, load the tile using provideTile on the tile provider and copy the bytes to see if they reveal anything
• Check the tile loading interceptor
• If you can export a small store with error tiles, you can send it to me and I'll see what I can do when I get time.

[codeOfJannik]

Thanks for your reply! I will continue debugging with your suggestions and let you know once I have found something.

[codeOfJannik]

@JaffaKetchup Apparently there is no problem that broken tiles are cached. We were able to reolve the behaviour by:

1. Adding a RetryClient as HttpClient of the TileProvider
2. Emit a reset event on the TileLayer once we detect a network connected event (disconnected -> connected)

[JaffaKetchup]

Glad you could fix it! I wonder if the Flutter image cache was causing problems again (caching the failed response and using it before it could actually use FMTC logic). Are you running v10 or the v11 prerelease?

[codeOfJannik]

We use the v11 prerelease