Merge pull request #674 from Hixie/duplicate-keys-in-stocks

Fix crash when going back in stocks app.

examples/stocks/lib/stock_home.dart

@@ -199,8 +199,9 @@ class StockHomeState extends State<StockHome> {
     ));
   }
 
-  Widget buildStockList(BuildContext context, Iterable<Stock> stocks) {
+  Widget _buildStockList(BuildContext context, Iterable<Stock> stocks, StockHomeTab tab) {
     return new StockList(
+      keySalt: tab,
       stocks: stocks.toList(),
       onAction: _buyStock,
       onOpen: (Stock stock, Key arrowKey) {
@@ -214,6 +215,13 @@ class StockHomeState extends State<StockHome> {
     );
   }
 
+  Widget _buildStockTab(BuildContext context, StockHomeTab tab, List<String> stockSymbols) {
+    return new Container(
+      key: new ValueKey<StockHomeTab>(tab),
+      child: _buildStockList(context, _filterBySearchQuery(_getStockList(stockSymbols)).toList(), tab)
+    );
+  }
+
   static const List<String> portfolioSymbols = const <String>["AAPL","FIZZ", "FIVE", "FLAT", "ZINC", "ZNGA"];
 
   static GlobalKey searchFieldKey = new GlobalKey();
@@ -259,13 +267,6 @@ class StockHomeState extends State<StockHome> {
     );
   }
 
-  Widget buildStockTab(BuildContext context, StockHomeTab tab, List<String> stockSymbols) {
-    return new Container(
-      key: new ValueKey<StockHomeTab>(tab),
-      child: buildStockList(context, _filterBySearchQuery(_getStockList(stockSymbols)).toList())
-    );
-  }
-
   double _viewWidth = 100.0;
   void _handleSizeChanged(Size newSize) {
     setState(() {
@@ -282,14 +283,14 @@ class StockHomeState extends State<StockHome> {
         onSizeChanged: _handleSizeChanged,
         child: new TabBarView<StockHomeTab>(
           selection: _tabBarSelection,
-          items: [StockHomeTab.market, StockHomeTab.portfolio],
+          items: <StockHomeTab>[StockHomeTab.market, StockHomeTab.portfolio],
           itemExtent: _viewWidth,
           itemBuilder: (BuildContext context, StockHomeTab tab, _) {
             switch (tab) {
               case StockHomeTab.market:
-                return buildStockTab(context, tab, config.symbols);
+                return _buildStockTab(context, tab, config.symbols);
               case StockHomeTab.portfolio:
-                return buildStockTab(context, tab, portfolioSymbols);
+                return _buildStockTab(context, tab, portfolioSymbols);
               default:
                 assert(false);
             }

examples/stocks/lib/stock_list.dart

@@ -5,8 +5,9 @@
 part of stocks;
 
 class StockList extends StatelessComponent {
-  StockList({ Key key, this.stocks, this.onOpen, this.onShow, this.onAction }) : super(key: key);
+  StockList({ Key key, this.keySalt, this.stocks, this.onOpen, this.onShow, this.onAction }) : super(key: key);
 
+  final Object keySalt;
   final List<Stock> stocks;
   final StockRowActionCallback onOpen;
   final StockRowActionCallback onShow;
@@ -18,6 +19,7 @@ class StockList extends StatelessComponent {
       itemExtent: StockRow.kHeight,
       itemBuilder: (BuildContext context, Stock stock, int index) {
         return new StockRow(
+          keySalt: keySalt,
           stock: stock,
           onPressed: onOpen,
           onDoubleTap: onShow,

examples/stocks/lib/stock_row.dart

@@ -7,18 +7,22 @@ part of stocks;
 enum StockRowPartKind { arrow }
 
 class StockRowPartKey extends Key {
-  const StockRowPartKey(this.stock, this.part) : super.constructor();
+  const StockRowPartKey(this.keySalt, this.stock, this.part) : super.constructor();
+  final Object keySalt;
   final Stock stock;
   final StockRowPartKind part;
   bool operator ==(dynamic other) {
-    if (other is! StockRowPartKey)
+    if (identical(this, other))
+      return true;
+    if (other.runtimeType != runtimeType)
       return false;
     final StockRowPartKey typedOther = other;
-    return stock == typedOther.stock &&
-           part == typedOther.part;
+    return keySalt == typedOther.keySalt
+        && stock == typedOther.stock
+        && part == typedOther.part;
   }
-  int get hashCode => 37 * (37 * (373) + identityHashCode(stock)) + identityHashCode(part);
-  String toString() => '[StockRowPartKey ${stock.symbol}:${part.toString().split(".")[1]})]';
+  int get hashCode => 37 * (37 * (37 * (373) + identityHashCode(keySalt)) + identityHashCode(stock)) + identityHashCode(part);
+  String toString() => '[$runtimeType ${keySalt.toString().split(".")[1]}:${stock.symbol}:${part.toString().split(".")[1]}]';
 }
 
 typedef void StockRowActionCallback(Stock stock, Key arrowKey);
@@ -26,11 +30,12 @@ typedef void StockRowActionCallback(Stock stock, Key arrowKey);
 class StockRow extends StatelessComponent {
   StockRow({
     Stock stock,
+    Object keySalt,
     this.onPressed,
     this.onDoubleTap,
     this.onLongPressed
   }) : this.stock = stock,
-       _arrowKey = new StockRowPartKey(stock, StockRowPartKind.arrow),
+       _arrowKey = new StockRowPartKey(keySalt, stock, StockRowPartKind.arrow),
        super(key: new ObjectKey(stock));
 
   final Stock stock;

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

@@ -88,6 +88,8 @@ class HeroController extends NavigatorObserver {
   }
 
   Set<Key> _getMostValuableKeys() {
+    assert(_from != null);
+    assert(_to != null);
     Set<Key> result = new Set<Key>();
     if (_from.settings.mostValuableKeys != null)
       result.addAll(_from.settings.mostValuableKeys);

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

@@ -107,7 +107,19 @@ class Hero extends StatefulComponent {
         assert(tag != null);
         Key key = hero.widget.key;
         final Map<Key, HeroState> tagHeroes = heroes.putIfAbsent(tag, () => <Key, HeroState>{});
-        assert(!tagHeroes.containsKey(key));
+        assert(() {
+          if (tagHeroes.containsKey(key)) {
+            debugPrint('Tag: $tag   Key: $key');
+            assert(() {
+              'There are multiple heroes that share the same key within the same subtree.               '
+              'Within each subtree for which heroes are to be animated (typically a PageRoute subtree), '
+              'either each Hero must have a unique tag, or, all the heroes with a particular tag must   '
+              'have different keys. The relevant tag and key were dumped above.                         ';
+              return false;
+            });
+          }
+          return true;
+        });
         tagHeroes[key] = hero.state;
       }
       element.visitChildren(visitor);