fix(mobile): handle image stream completion when no image is emitted (#25984)

* Fix image cancellation to be stream-scoped instead of widget-scoped

* fix(OneFramePlaceholderImageStreamCompleter): make onLastListenerRemoved callback synchronous with removing the last listener

* fix(OneFrameMultiImageStreamCompleter): remove unnecessary blank line in code

* fix(OneFramePlaceholderImageStreamCompleter): cancel pending requests when only cache listener remains

* fix(OneFrameMultiImageStreamCompleter): ensure onLastListenerRemoved callback is invoked only once

mobile/lib/presentation/widgets/images/local_image_provider.dart

@@ -31,7 +31,7 @@ class LocalThumbProvider extends CancellableImageProvider<LocalThumbProvider>
         DiagnosticsProperty<String>('Id', key.id),
         DiagnosticsProperty<Size>('Size', key.size),
       ],
-      onDispose: cancel,
+      onLastListenerRemoved: cancel,
     );
   }
 
@@ -76,7 +76,7 @@ class LocalFullImageProvider extends CancellableImageProvider<LocalFullImageProv
         DiagnosticsProperty<String>('Id', key.id),
         DiagnosticsProperty<Size>('Size', key.size),
       ],
-      onDispose: cancel,
+      onLastListenerRemoved: cancel,
     );
   }
 

mobile/lib/presentation/widgets/images/one_frame_multi_image_stream_completer.dart

@@ -9,7 +9,10 @@ import 'package:flutter/painting.dart';
 
 /// An ImageStreamCompleter with support for loading multiple images.
 class OneFramePlaceholderImageStreamCompleter extends ImageStreamCompleter {
-  void Function()? _onDispose;
+  void Function()? _onLastListenerRemoved;
+  int _listenerCount = 0;
+  // True once setImage() has been called at least once.
+  bool didProvideImage = false;
 
   /// The constructor to create an OneFramePlaceholderImageStreamCompleter. The [images]
   /// should be the primary images to display (typically asynchronously as they load).
@@ -19,14 +22,18 @@ class OneFramePlaceholderImageStreamCompleter extends ImageStreamCompleter {
     Stream<ImageInfo> images, {
     ImageInfo? initialImage,
     InformationCollector? informationCollector,
-    void Function()? onDispose,
+    void Function()? onLastListenerRemoved,
   }) {
     if (initialImage != null) {
+      didProvideImage = true;
       setImage(initialImage);
     }
-    _onDispose = onDispose;
+    _onLastListenerRemoved = onLastListenerRemoved;
     images.listen(
-      setImage,
+      (image) {
+        didProvideImage = true;
+        setImage(image);
+      },
       onError: (Object error, StackTrace stack) {
         reportError(
           context: ErrorDescription('resolving a single-frame image stream'),
@@ -40,12 +47,24 @@ class OneFramePlaceholderImageStreamCompleter extends ImageStreamCompleter {
   }
 
   @override
-  void onDisposed() {
-    final onDispose = _onDispose;
-    if (onDispose != null) {
-      _onDispose = null;
-      onDispose();
+  void addListener(ImageStreamListener listener) {
+    super.addListener(listener);
+    _listenerCount = _listenerCount + 1;
+  }
+
+  @override
+  void removeListener(ImageStreamListener listener) {
+    super.removeListener(listener);
+    _listenerCount = _listenerCount - 1;
+
+    final bool onlyCacheListenerLeft = _listenerCount == 1 && !didProvideImage;
+    final bool noListenersAfterImage = _listenerCount == 0 && didProvideImage;
+
+    final onLastListenerRemoved = _onLastListenerRemoved;
+
+    if (onLastListenerRemoved != null && (noListenersAfterImage || onlyCacheListenerLeft)) {
+      _onLastListenerRemoved = null;
+      onLastListenerRemoved();
     }
-    super.onDisposed();
   }
 }

mobile/lib/presentation/widgets/images/remote_image_provider.dart

@@ -32,7 +32,7 @@ class RemoteImageProvider extends CancellableImageProvider<RemoteImageProvider>
         DiagnosticsProperty<ImageProvider>('Image provider', this),
         DiagnosticsProperty<String>('URL', key.url),
       ],
-      onDispose: cancel,
+      onLastListenerRemoved: cancel,
     );
   }
 
@@ -76,7 +76,7 @@ class RemoteFullImageProvider extends CancellableImageProvider<RemoteFullImagePr
         DiagnosticsProperty<ImageProvider>('Image provider', this),
         DiagnosticsProperty<String>('Asset Id', key.assetId),
       ],
-      onDispose: cancel,
+      onLastListenerRemoved: cancel,
     );
   }
 

mobile/lib/presentation/widgets/images/thumb_hash_provider.dart

@@ -17,7 +17,7 @@ class ThumbHashProvider extends CancellableImageProvider<ThumbHashProvider>
 
   @override
   ImageStreamCompleter loadImage(ThumbHashProvider key, ImageDecoderCallback decode) {
-    return OneFramePlaceholderImageStreamCompleter(_loadCodec(key, decode), onDispose: cancel);
+    return OneFramePlaceholderImageStreamCompleter(_loadCodec(key, decode), onLastListenerRemoved: cancel);
   }
 
   Stream<ImageInfo> _loadCodec(ThumbHashProvider key, ImageDecoderCallback decode) {

mobile/lib/presentation/widgets/images/thumbnail.widget.dart

@@ -233,16 +233,6 @@ class _ThumbnailState extends State<Thumbnail> with SingleTickerProviderStateMix
 
   @override
   void dispose() {
-    final imageProvider = widget.imageProvider;
-    if (imageProvider is CancellableImageProvider) {
-      imageProvider.cancel();
-    }
-
-    final thumbhashProvider = widget.thumbhashProvider;
-    if (thumbhashProvider is CancellableImageProvider) {
-      thumbhashProvider.cancel();
-    }
-
     _fadeController.removeStatusListener(_onAnimationStatusChanged);
     _fadeController.dispose();
     _stopListeningToStream();