🐛 Fix disposed provider throwing error when fetching assets (#493)

Co-authored-by: Alex Li <[email protected]>

Author: LeGoffMael

lib/src/provider/asset_picker_provider.dart

@@ -60,9 +60,21 @@ abstract class AssetPickerProvider<Asset, Path> extends ChangeNotifier {
     _paths.clear();
     _currentPath = null;
     _currentAssets.clear();
+    _mounted = false;
     super.dispose();
   }
 
+  @override
+  void notifyListeners() {
+    if (_mounted) {
+      super.notifyListeners();
+    }
+  }
+
+  /// Whether the provider is mounted. Set to `false` if disposed.
+  bool get mounted => _mounted;
+  bool _mounted = true;
+
   /// Get paths.
   /// 获取所有的资源路径
   Future<void> getPaths();
@@ -490,6 +502,10 @@ class DefaultAssetPickerProvider
     final PathWrapper<AssetPathEntity> wrapper = _currentPath!;
     final int assetCount =
         wrapper.assetCount ?? await wrapper.path.assetCountAsync;
+    // If the picker was disposed (#492), stop fetching the assets
+    if (!mounted) {
+      return;
+    }
     totalAssetsCount = assetCount;
     isAssetsEmpty = assetCount == 0;
     if (wrapper.assetCount == null) {