onStyleLoaded never fires on Android

[sirawatGG]

Platforms

Android

Version of flutter-maplibre

0.3.3+2

Bug Description

onStyleLoaded (and MapEventStyleLoaded) never fires on Android. The map loads visually but the callback is never invoked.

Ai was able to resolve this issue by this code change

1. Missing onStyleLoaded$async = true
   The JNI bridge defaults to onStyleLoaded$async = false, which attempts to call Dart synchronously from the Android main thread. Since Dart runs on a separate isolate, this is undefined behavior and silently fails.

Compare: _CameraMovementCallback correctly sets onCancel$async = true and onFinish$async = true, but _StyleLoadedCallback was missing the equivalent.

2. WeakReference wrapping a method tearoff
   // Before (broken)

_StyleLoadedCallback(WeakReference(onStyleLoaded))
onStyleLoaded written this way creates a temporary tearoff object with no strong holder. Dart's GC collects it almost immediately. By the time MapLibre fires the callback asynchronously (after downloading/parsing the style), weakCallback.target is null and the callback does nothing.

Steps to Reproduce

1. Run on an Android device or emulator
2. Wait for the map to fully render
3. Observe that onStyleLoaded is never called — no print, no state update, nothing

Expected Results

It should call onStyleLoaded

Actual Results

It never call onStyleLoaded

[sszajbely]

Just to add to this, I have observed the same behavior (map loads visually but onStyleLoaded is never called) on iOS on version 0.3.3+1. I've never actually observed it on android though.

[josxha]

Not sure how to reproduce this issue, it works fine for me. @sirawatGG could you post a video showcasing the problem so that I have a better chance to reproduce it?

---

@sszajbely Yes, I think there was a problem in calling the onStyleLoaded callback on iOS. It should be resolved on the main branch if I'm not mistaken. If the problem persists after the 0.3.4 release, let me know and I'll take another look.

[sszajbely]

Hi, thank you for the answer @josxha. I've tried out the new version and sadly the issue still persists. AI seemingly was able to track down the issue which was (apparently) due to the sync nature of the local json loading and the flutter api not being available at that time resulting in a race condition. I'm not sure if this makes sense as I do not know anything about platform specific code, but the changes seem to have fixed the issue.

In MapLibreView.swift it changed lines 34-37 to

_mapView.autoresizingMask = [.flexibleWidth, .flexibleHeight]  
MapLibreRegistry.addMap(viewId: viewId, map: _mapView)  
_view.addSubview(_mapView)  
  
// Defer delegate setting to ensure FlutterApi is registered first  
// Poll for api availability since style might load synchronously  
waitForApiAndSetDelegate()  

where waitForApiAndSetDelegate is defined as

private func waitForApiAndSetDelegate(attempt: Int = 0) {  
  if api != nil {  
  // Api is ready, set delegate  
  _mapView.delegate = self  
    
  // If style was already loaded before delegate was set, manually trigger the callback  
  if let style = _[mapView.style](http://mapview.style/) {  
    mapView(_mapView, didFinishLoading: style)  
  }  
  } else if attempt < 20 {  
    // Api not ready yet, retry after a short delay (max 2 seconds)  
    DispatchQueue.main.asyncAfter(deadline: .now() + 0.1) { [weak self] in  
    self?.waitForApiAndSetDelegate(attempt: attempt + 1)  
  }  
  } else {  
    // Timeout: set delegate anyway to at least catch future events  
    _mapView.delegate = self  
  }  
}

As I said, I don't know if this is a correct fix, but it has fixed the issue for me at least, so I'm posting it just to let you know.