Avoid accessing bounds of widget that has never been laid out (#424)

Fixes a bug in visibility_detector.

Author: dnfield

packages/visibility_detector/CHANGELOG.md

@@ -1,5 +1,9 @@
 # CHANGELOG
 
+## 0.4.0+2
+
+* Fix a bug for updates to render objects that have not been laid out yet.
+
 ## 0.4.0+1
 
 * Correct Flutter SDK version dependency to 3.1.0.

packages/visibility_detector/lib/src/render_visibility_detector.dart

@@ -140,7 +140,14 @@ mixin RenderVisibilityDetectorBase on RenderObject {
     }
     bool isFirstUpdate = _updates.isEmpty;
     _updates[key] = () {
-      _fireCallback(layer, bounds);
+      if (bounds == null) {
+        // This can happen if set onVisibilityChanged was called with a non-null
+        // value but this render object has not been laid out. In that case,
+        // it has no size or geometry, and we should not worry about firing
+        // an update since it never has been visible.
+        return;
+      }
+      _fireCallback(layer, bounds!);
     };
     final updateInterval = VisibilityDetectorController.instance.updateInterval;
     if (updateInterval == Duration.zero) {
@@ -228,7 +235,9 @@ mixin RenderVisibilityDetectorBase on RenderObject {
 
   /// Used to get the bounds of the render object when it is time to update
   /// clients about visibility.
-  Rect get bounds;
+  ///
+  /// A null value means bounds are not available.
+  Rect? get bounds;
 
   Matrix4? _lastPaintTransform;
   Rect? _lastPaintClipBounds;
@@ -280,7 +289,7 @@ class RenderVisibilityDetector extends RenderProxyBox
   final Key key;
 
   @override
-  Rect get bounds => semanticBounds;
+  Rect? get bounds => hasSize ? semanticBounds : null;
 }
 
 /// The [RenderObject] corresponding to the [SliverVisibilityDetector] widget.
@@ -302,7 +311,11 @@ class RenderSliverVisibilityDetector extends RenderProxySliver
   final Key key;
 
   @override
-  Rect get bounds {
+  Rect? get bounds {
+    if (geometry == null) {
+      return null;
+    }
+
     Size widgetSize;
     Offset widgetOffset;
     switch (applyGrowthDirectionToAxisDirection(

packages/visibility_detector/pubspec.yaml

@@ -1,5 +1,5 @@
 name: visibility_detector
-version: 0.4.0+1
+version: 0.4.0+2
 description: >
   A widget that detects the visibility of its child and notifies a callback.
 repository: https://github.com/google/flutter.widgets/tree/master/packages/visibility_detector

packages/visibility_detector/test/render_visibility_detector_test.dart

@@ -134,4 +134,44 @@ void main() {
 
     expect(detector.debugScheduleUpdateCount, 0);
   });
+
+  testWidgets('RVS can schedule an update for a RO that is not laid out',
+      (WidgetTester tester) async {
+    final RenderVisibilityDetector detector = RenderVisibilityDetector(
+      key: Key('test'),
+      onVisibilityChanged: (_) {
+        fail('should not get called');
+      },
+    );
+
+    // Force an out of band update to get scheduled without laying out.
+    detector.onVisibilityChanged = (_) {
+      fail('This should also not get called');
+    };
+
+    expect(detector.debugScheduleUpdateCount, 1);
+
+    detector.dispose();
+  });
+
+  testWidgets(
+      'RVS (Sliver) can schedule an update for a RO that is not laid out',
+      (WidgetTester tester) async {
+    final RenderSliverVisibilityDetector detector =
+        RenderSliverVisibilityDetector(
+      key: Key('test'),
+      onVisibilityChanged: (_) {
+        fail('should not get called');
+      },
+    );
+
+    // Force an out of band update to get scheduled without laying out.
+    detector.onVisibilityChanged = (_) {
+      fail('This should also not get called');
+    };
+
+    expect(detector.debugScheduleUpdateCount, 1);
+
+    detector.dispose();
+  });
 }