iOS crash with geo json source on symbol layer?

[sqcsabbey]

I'm trying to use a symbol layer to show a dynamic location on the map, but I'm getting a crash with iOS (works on Android). I'm not sure if I'm doing something wrong or not; I was hoping someone could either tell me how I'm calling MapLibre incorrectly, or let me know it's a bug so I can write up an issue.

In the onStyleLoadedCallback, I have:

      await _maplibreController.removeSource(_symbolSource);
      await _maplibreController.addGeoJsonSource(
          _symbolSource, {"type": "FeatureCollection", "features": []});

      var crossHairsLayerId = "$_symbolSource-layer";
      var crossHairsIconName = "$_symbolSource-icon";
      await addImageFromAsset(_maplibreController, crossHairsIconName,
          "assets/map/sensor_location.png");

      await _maplibreController.removeLayer(crossHairsLayerId);
      await _maplibreController.addLayer(
          _symbolSource,
          crossHairsLayerId,
          SymbolLayerProperties(
              iconImage:
                  crossHairsIconName), //, visibility: Visibility.visible),
          belowLayerId: "com.mapbox.annotations.points",
          enableInteraction: false);

I'm adding the source here so I can call setGeoJsonSource whenever my dynamic location gets updated.

The crash comes when I use _symbolSource as the sourceId in the addLayer call; the _symbolSource value ("sensor_location") shows in an error message of Source sensor_location already exists.

... and here's the full stack trace:

Fatal Exception: MGLRedundantSourceIdentifierException
0  CoreFoundation                 0xec870 __exceptionPreprocess
1  libobjc.A.dylib                0x2bc00 objc_exception_throw
2  CoreFoundation                 0x171654 -[NSException initWithCoder:]
3  Mapbox                         0x3971fc -[MGLStyle addSource:] + 215 (MGLStyle.mm:215)
4  maplibre_gl                    0x1c574 MapboxMapController.addSourceGeojson(sourceId:geojson:) + 1431 (MapboxMapController.swift:1431)
5  maplibre_gl                    0x1744c MapboxMapController.onMethodCall(methodCall:result:) + 715 (MapboxMapController.swift:715)
6  maplibre_gl                    0x1013c closure #1 in MapboxMapController.init(withFrame:viewIdentifier:arguments:registrar:) + 51 (MapboxMapController.swift:51)
7  maplibre_gl                    0x2c864 thunk for @escaping @callee_guaranteed (@guaranteed FlutterMethodCall, @guaranteed @escaping @callee_guaranteed (@in_guaranteed Any?) -> ()) -> () (<compiler-generated>)
8  Flutter                        0x5d6050 (Missing UUID 4c4c448255553144a1489826506458ca)
9  Flutter                        0x435a4 (Missing UUID 4c4c448255553144a1489826506458ca)
10 libdispatch.dylib              0x26a8 _dispatch_call_block_and_release
11 libdispatch.dylib              0x4300 _dispatch_client_callout
12 libdispatch.dylib              0x12998 _dispatch_main_queue_drain
13 libdispatch.dylib              0x125b0 _dispatch_main_queue_callback_4CF
14 CoreFoundation                 0x3720c __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__
15 CoreFoundation                 0x33f18 __CFRunLoopRun
16 CoreFoundation                 0x33668 CFRunLoopRunSpecific
17 GraphicsServices               0x35ec GSEventRunModal
18 UIKitCore                      0x22c2b4 -[UIApplication _run]
19 UIKitCore                      0x22b8f0 UIApplicationMain
20 Runner                         0x6628 main + 5 (AppDelegate.swift:5)
21 ???                            0x1ba91edcc (Missing)

[m0nac0]

This seems like a bug. It seems that the layer is not actually deleted when await _maplibreController.removeSource(_symbolSource); completes.

Can you try to wait a second between the first and the second line of your snippet (e.g. with await Future.delayed(const Duration(seconds: 1));, or less time should probably also be sufficient)?

[sqcsabbey]

If I change _symbolSource to crossHairsLayerId in the _maplibreController.addLayer call, then I don't get the crash, but then this source is not tied to this layer, so nothing shows.

I think this means that the addLayer call is also adding this source in the Swift code?

[m0nac0]

But the stacktrace says the exception comes from MapboxMapController.addSourceGeojson (on the swift side) and that is only called when you call MaplibreMapController.addGeoJsonSource (on the dart side)

[sqcsabbey]

Ok, I tried it. I also synchronized the calls in a block because onStyleLoaded can get called multiple times... here's what I tried:

      await _symbolLock.synchronized(() async {
        await _maplibreController.removeSource(_symbolSource);
        await Future.delayed(const Duration(seconds: 1));
        await _maplibreController.addGeoJsonSource(
            _symbolSource, {"type": "FeatureCollection", "features": []});
      });

... and here's the stack trace, from Xcode:

Thread#0	0x00000001a7fd8870 in __exceptionPreprocess ()
#1	0x00000001a02f3c00 in objc_exception_throw ()
#2	0x00000001a805d654 in +[NSException raise:format:] ()
#3	0x00000001063a31fc in -[MGLStyle addSource:] at /Users/bart/src/maplibre-native/platform/ios/platform/darwin/src/MGLStyle.mm:214
#4	0x0000000105e154ac in MapboxMapController.addSourceGeojson(sourceId:geojson:) at /Users/csabbey/homebrew/Caskroom/flutter/3.0.0/flutter/.pub-cache/git/flutter-maplibre-gl-81e35d7e8950ff06fcbf8a63c2324502b915d0cb/ios/Classes/MapboxMapController.swift:1431
#5	0x0000000105e08e24 in MapboxMapController.onMethodCall(methodCall:result:) at /Users/csabbey/homebrew/Caskroom/flutter/3.0.0/flutter/.pub-cache/git/flutter-maplibre-gl-81e35d7e8950ff06fcbf8a63c2324502b915d0cb/ios/Classes/MapboxMapController.swift:715
#6	0x0000000105df56ac in closure #1 in MapboxMapController.init(withFrame:viewIdentifier:arguments:registrar:) at /Users/csabbey/homebrew/Caskroom/flutter/3.0.0/flutter/.pub-cache/git/flutter-maplibre-gl-81e35d7e8950ff06fcbf8a63c2324502b915d0cb/ios/Classes/MapboxMapController.swift:51
#7	0x0000000105df5758 in thunk for @escaping @callee_guaranteed (@guaranteed FlutterMethodCall, @guaranteed @escaping @callee_guaranteed (@in_guaranteed Any?) -> ()) -> () ()
#8	0x0000000109953f0c in __45-[FlutterMethodChannel setMethodCallHandler:]_block_invoke ()
#9	0x00000001093b8e1c in invocation function for block in flutter::PlatformMessageHandlerIos::HandlePlatformMessage(std::_LIBCPP_ABI_NAMESPACE::unique_ptr<flutter::PlatformMessage, std::_LIBCPP_ABI_NAMESPACE::default_delete<flutter::PlatformMessage>>) ()
#10	0x0000000105f58f50 in _dispatch_call_block_and_release ()
#11	0x0000000105f5ab34 in _dispatch_client_callout ()
#12	0x0000000105f6afec in _dispatch_main_queue_drain ()
#13	0x0000000105f6aba0 in _dispatch_main_queue_callback_4CF ()
#14	0x00000001a7f2320c in __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ ()
#15	0x00000001a7f1ff18 in __CFRunLoopRun ()
#16	0x00000001a7f1f668 in CFRunLoopRunSpecific ()
#17	0x00000001eb2ea5ec in GSEventRunModal ()
#18	0x00000001aa33c2b4 in -[UIApplication _run] ()
#19	0x00000001aa33b8f0 in UIApplicationMain ()
#20	0x0000000104181ba0 in main at /Users/csabbey/code/sqsurvey-flutter/ios/Runner/AppDelegate.swift:5
#21	0x00000001ca972dcc in start ()

[sqcsabbey]

Got my code working by removing the layer using the source before removing the source.

It looks like the source can't be removed if it's on a layer; this was failing the 2nd time my onStyleLoadedCallback was called.

[m0nac0]

Ah, that makes sense, thanks for sharing your solution.