Fix Scrollable.of()

Make ancestorStateOfType() and ancestorRenderObjectOfType() support
subclassing.

Fixes https://github.com/flutter/flutter/issues/1087

packages/flutter/lib/src/material/debug.dart

@@ -8,7 +8,7 @@ import 'material.dart';
 
 bool debugCheckHasMaterial(BuildContext context) {
   assert(() {
-    if (context.widget is Material || context.ancestorWidgetOfType(Material) != null)
+    if (context.widget is Material || context.ancestorWidgetOfExactType(Material) != null)
       return true;
     Element element = context;
     debugPrint('${context.widget} needs to be placed inside a Material widget. Ownership chain:\n${element.debugGetOwnershipChain(10)}');

packages/flutter/lib/src/material/icon_theme.dart

@@ -20,7 +20,7 @@ class IconTheme extends InheritedWidget {
 
   /// The data from the closest instance of this class that encloses the given context.
   static IconThemeData of(BuildContext context) {
-    IconTheme result = context.inheritFromWidgetOfType(IconTheme);
+    IconTheme result = context.inheritFromWidgetOfExactType(IconTheme);
     return result?.data;
   }
 

packages/flutter/lib/src/material/material.dart

@@ -95,7 +95,7 @@ class Material extends StatefulComponent {
 
   /// The ink controller from the closest instance of this class that encloses the given context.
   static MaterialInkController of(BuildContext context) {
-    final RenderInkFeatures result = context.ancestorRenderObjectOfType(RenderInkFeatures);
+    final RenderInkFeatures result = context.ancestorRenderObjectOfType(const TypeMatcher<RenderInkFeatures>());
     return result;
   }
 

packages/flutter/lib/src/material/material_button.dart

@@ -27,7 +27,7 @@ class ButtonTheme extends InheritedWidget {
   ///
   /// Defaults to [ButtonColor.normal] if none exists.
   static ButtonColor of(BuildContext context) {
-    ButtonTheme result = context.inheritFromWidgetOfType(ButtonTheme);
+    ButtonTheme result = context.inheritFromWidgetOfExactType(ButtonTheme);
     return result?.color ?? ButtonColor.normal;
   }
 

packages/flutter/lib/src/material/scaffold.dart

@@ -110,7 +110,7 @@ class Scaffold extends StatefulComponent {
   final Widget drawer;
 
   /// The state from the closest instance of this class that encloses the given context.
-  static ScaffoldState of(BuildContext context) => context.ancestorStateOfType(ScaffoldState);
+  static ScaffoldState of(BuildContext context) => context.ancestorStateOfType(const TypeMatcher<ScaffoldState>());
 
   ScaffoldState createState() => new ScaffoldState();
 }

packages/flutter/lib/src/material/theme.dart

@@ -26,7 +26,7 @@ class Theme extends InheritedWidget {
   ///
   /// Defaults to the fallback theme data if none exists.
   static ThemeData of(BuildContext context) {
-    Theme theme = context.inheritFromWidgetOfType(Theme);
+    Theme theme = context.inheritFromWidgetOfExactType(Theme);
     return theme?.data ?? _kFallbackTheme;
   }
 

packages/flutter/lib/src/widgets/basic.dart

@@ -1411,7 +1411,7 @@ class DefaultTextStyle extends InheritedWidget {
 
   /// The style from the closest instance of this class that encloses the given context.
   static TextStyle of(BuildContext context) {
-    DefaultTextStyle result = context.inheritFromWidgetOfType(DefaultTextStyle);
+    DefaultTextStyle result = context.inheritFromWidgetOfExactType(DefaultTextStyle);
     return result?.style;
   }
 
@@ -1737,7 +1737,7 @@ class DefaultAssetBundle extends InheritedWidget {
 
   /// The bundle from the closest instance of this class that encloses the given context.
   static AssetBundle of(BuildContext context) {
-    DefaultAssetBundle result = context.inheritFromWidgetOfType(DefaultAssetBundle);
+    DefaultAssetBundle result = context.inheritFromWidgetOfExactType(DefaultAssetBundle);
     return result?.bundle;
   }
 

packages/flutter/lib/src/widgets/focus.dart

@@ -89,7 +89,7 @@ class Focus extends StatefulComponent {
     assert(context.widget != null);
     assert(context.widget.key != null);
     assert(context.widget.key is GlobalKey);
-    _FocusScope focusScope = context.inheritFromWidgetOfType(_FocusScope);
+    _FocusScope focusScope = context.inheritFromWidgetOfExactType(_FocusScope);
     if (focusScope != null) {
       if (autofocus)
         focusScope._setFocusedWidgetIfUnset(context.widget.key);
@@ -113,7 +113,7 @@ class Focus extends StatefulComponent {
     assert(context != null);
     assert(context.widget != null);
     assert(context.widget is Focus);
-    _FocusScope focusScope = context.inheritFromWidgetOfType(_FocusScope);
+    _FocusScope focusScope = context.inheritFromWidgetOfExactType(_FocusScope);
     if (focusScope != null) {
       assert(context.widget.key != null);
       if (autofocus)
@@ -131,7 +131,7 @@ class Focus extends StatefulComponent {
   /// called from event listeners, e.g. in response to a finger tap or tab key.
   static void moveTo(GlobalKey key) {
     assert(key.currentContext != null);
-    _FocusScope focusScope = key.currentContext.ancestorWidgetOfType(_FocusScope);
+    _FocusScope focusScope = key.currentContext.ancestorWidgetOfExactType(_FocusScope);
     if (focusScope != null)
       focusScope.focusState._setFocusedWidget(key);
   }
@@ -144,7 +144,7 @@ class Focus extends StatefulComponent {
   static void moveScopeTo(GlobalKey key) {
     assert(key.currentWidget is Focus);
     assert(key.currentContext != null);
-    _FocusScope focusScope = key.currentContext.ancestorWidgetOfType(_FocusScope);
+    _FocusScope focusScope = key.currentContext.ancestorWidgetOfExactType(_FocusScope);
     if (focusScope != null)
       focusScope.focusState._setFocusedScope(key);
   }

packages/flutter/lib/src/widgets/framework.dart

@@ -198,6 +198,11 @@ class GlobalObjectKey extends GlobalKey {
   String toString() => '[$runtimeType ${value.runtimeType}(${value.hashCode})]';
 }
 
+/// This class is a work-around for the "is" operator not accepting a variable value as its right operand
+class TypeMatcher<T> {
+  const TypeMatcher();
+  bool check(dynamic object) => object is T;
+}
 
 // WIDGETS
 
@@ -585,10 +590,10 @@ typedef void ElementVisitor(Element element);
 abstract class BuildContext {
   Widget get widget;
   RenderObject findRenderObject();
-  InheritedWidget inheritFromWidgetOfType(Type targetType);
-  Widget ancestorWidgetOfType(Type targetType);
-  State ancestorStateOfType(Type targetType);
-  RenderObject ancestorRenderObjectOfType(Type targetType);
+  InheritedWidget inheritFromWidgetOfExactType(Type targetType);
+  Widget ancestorWidgetOfExactType(Type targetType);
+  State ancestorStateOfType(TypeMatcher matcher);
+  RenderObject ancestorRenderObjectOfType(TypeMatcher matcher);
   void visitAncestorElements(bool visitor(Element element));
   void visitChildElements(void visitor(Element element));
 }
@@ -876,24 +881,24 @@ abstract class Element<T extends Widget> implements BuildContext {
   RenderObject findRenderObject() => renderObject;
 
   Set<Type> _dependencies;
-  InheritedWidget inheritFromWidgetOfType(Type targetType) {
+  InheritedWidget inheritFromWidgetOfExactType(Type targetType) {
     if (_dependencies == null)
       _dependencies = new Set<Type>();
     _dependencies.add(targetType);
-    return ancestorWidgetOfType(targetType);
+    return ancestorWidgetOfExactType(targetType);
   }
 
-  Widget ancestorWidgetOfType(Type targetType) {
+  Widget ancestorWidgetOfExactType(Type targetType) {
     Element ancestor = _parent;
     while (ancestor != null && ancestor.widget.runtimeType != targetType)
       ancestor = ancestor._parent;
     return ancestor?.widget;
   }
 
-  State ancestorStateOfType(Type targetType) {
+  State ancestorStateOfType(TypeMatcher matcher) {
     Element ancestor = _parent;
     while (ancestor != null) {
-      if (ancestor is StatefulComponentElement && ancestor.state.runtimeType == targetType)
+      if (ancestor is StatefulComponentElement && matcher.check(ancestor.state))
         break;
       ancestor = ancestor._parent;
     }
@@ -901,10 +906,10 @@ abstract class Element<T extends Widget> implements BuildContext {
     return statefulAncestor?.state;
   }
 
-  RenderObject ancestorRenderObjectOfType(Type targetType) {
+  RenderObject ancestorRenderObjectOfType(TypeMatcher matcher) {
     Element ancestor = _parent;
     while (ancestor != null) {
-      if (ancestor is RenderObjectElement && ancestor.renderObject.runtimeType == targetType)
+      if (ancestor is RenderObjectElement && matcher.check(ancestor.renderObject))
         break;
       ancestor = ancestor._parent;
     }

packages/flutter/lib/src/widgets/locale_query.dart

@@ -20,7 +20,7 @@ class LocaleQuery<T extends LocaleQueryData> extends InheritedWidget {
 
   /// The data from the closest instance of this class that encloses the given context.
   static LocaleQueryData of(BuildContext context) {
-    LocaleQuery query = context.inheritFromWidgetOfType(LocaleQuery);
+    LocaleQuery query = context.inheritFromWidgetOfExactType(LocaleQuery);
     return query == null ? null : query.data;
   }
 

packages/flutter/lib/src/widgets/media_query.dart

@@ -58,7 +58,7 @@ class MediaQuery extends InheritedWidget {
   /// When that information changes, your widget will be scheduled to be rebuilt,
   /// keeping your widget up-to-date.
   static MediaQueryData of(BuildContext context) {
-    MediaQuery query = context.inheritFromWidgetOfType(MediaQuery);
+    MediaQuery query = context.inheritFromWidgetOfExactType(MediaQuery);
     return query == null ? null : query.data;
   }
 

packages/flutter/lib/src/widgets/mimic.dart

@@ -111,7 +111,7 @@ class MimicOverlayEntry {
       }
     }
 
-    RenderBox stack = context.ancestorRenderObjectOfType(RenderStack);
+    RenderBox stack = context.ancestorRenderObjectOfType(const TypeMatcher<RenderStack>());
     // TODO(abarth): Handle the case where the transform here isn't just a translation.
     Point localPosition = stack == null ? globalPosition: stack.globalToLocal(globalPosition);
     return new Positioned(

packages/flutter/lib/src/widgets/navigator.dart

@@ -144,7 +144,7 @@ class Navigator extends StatefulComponent {
   }
 
   static bool canPop(BuildContext context) {
-    NavigatorState navigator = context.ancestorStateOfType(NavigatorState);
+    NavigatorState navigator = context.ancestorStateOfType(const TypeMatcher<NavigatorState>());
     return navigator != null && navigator.canPop();
   }
 
@@ -156,7 +156,7 @@ class Navigator extends StatefulComponent {
   }
 
   static void openTransaction(BuildContext context, NavigatorTransactionCallback callback) {
-    NavigatorState navigator = context.ancestorStateOfType(NavigatorState);
+    NavigatorState navigator = context.ancestorStateOfType(const TypeMatcher<NavigatorState>());
     navigator.openTransaction(callback);
   }
 

packages/flutter/lib/src/widgets/overlay.dart

@@ -69,7 +69,7 @@ class Overlay extends StatefulComponent {
   final List<OverlayEntry> initialEntries;
 
   /// The state from the closest instance of this class that encloses the given context.
-  static OverlayState of(BuildContext context) => context.ancestorStateOfType(OverlayState);
+  static OverlayState of(BuildContext context) => context.ancestorStateOfType(const TypeMatcher<OverlayState>());
 
   OverlayState createState() => new OverlayState();
 }

packages/flutter/lib/src/widgets/page_storage.dart

@@ -79,7 +79,7 @@ class PageStorage extends StatelessComponent {
   ///
   /// Returns null if none exists.
   static PageStorageBucket of(BuildContext context) {
-    PageStorage widget = context.ancestorWidgetOfType(PageStorage);
+    PageStorage widget = context.ancestorWidgetOfExactType(PageStorage);
     return widget?.bucket;
   }
 

packages/flutter/lib/src/widgets/routes.dart

@@ -388,7 +388,7 @@ abstract class ModalRoute<T> extends TransitionRoute<T> with LocalHistoryRoute<T
   ///
   /// Returns null if the given context is not associated with a modal route.
   static ModalRoute of(BuildContext context) {
-    _ModalScopeStatus widget = context.inheritFromWidgetOfType(_ModalScopeStatus);
+    _ModalScopeStatus widget = context.inheritFromWidgetOfExactType(_ModalScopeStatus);
     return widget?.route;
   }
 

packages/flutter/lib/src/widgets/scrollable.dart

@@ -59,7 +59,7 @@ abstract class Scrollable extends StatefulComponent {
 
   /// The state from the closest instance of this class that encloses the given context.
   static ScrollableState of(BuildContext context) {
-    return context.ancestorStateOfType(ScrollableState);
+    return context.ancestorStateOfType(const TypeMatcher<ScrollableState>());
   }
 
   /// Scrolls the closest enclosing scrollable to make the given context visible.

packages/flutter/test/widget/page_forward_transitions_test.dart

@@ -5,7 +5,7 @@
 import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/animation.dart';
 import 'package:flutter/material.dart';
-import 'package:test/test.dart';
+import 'package:test/test.dart' hide TypeMatcher;
 
 class TestTransition extends TransitionComponent {
   TestTransition({
@@ -99,7 +99,7 @@ void main() {
         )
       );
 
-      NavigatorState navigator = insideKey.currentContext.ancestorStateOfType(NavigatorState);
+      NavigatorState navigator = insideKey.currentContext.ancestorStateOfType(const TypeMatcher<NavigatorState>());
 
       expect(state(), equals('BC')); // transition ->1 is at 1.0