Turning `if` chains into shorter `switch` statements (#144977)

This pull request is part of the effort to solve issue #144903.

In the past, my efforts to reduce line length involved refactoring away from switch statements, but unlike [yesterday's PR](https://github.com/flutter/flutter/pull/144905), this one is full of switch statements that make things more concise!

dev/integration_tests/wide_gamut_test/lib/main.dart

@@ -259,18 +259,13 @@ class _MyHomePageState extends State<MyHomePage> {
 
   @override
   void initState() {
-    if (widget.setup == Setup.canvasSaveLayer) {
-      _loadImage().then((ui.Image? value) {
-        setState(() {
-          _image = value;
-        });
-      });
-    } else if (widget.setup == Setup.drawnImage) {
-      _drawImage().then((ui.Image? value) {
-        setState(() {
-          _image = value;
-        });
-      });
+    switch (widget.setup) {
+      case Setup.canvasSaveLayer:
+        _loadImage().then((ui.Image? value) => setState(() { _image = value; }));
+      case Setup.drawnImage:
+        _drawImage().then((ui.Image? value) => setState(() { _image = value; }));
+      case Setup.image || Setup.blur || Setup.none:
+        break;
     }
     super.initState();
   }

examples/api/lib/widgets/focus_manager/focus_node.0.dart

@@ -55,24 +55,19 @@ class _ColorfulButtonState extends State<ColorfulButton> {
   KeyEventResult _handleKeyPress(FocusNode node, KeyEvent event) {
     if (event is KeyDownEvent) {
       debugPrint('Focus node ${node.debugLabel} got key event: ${event.logicalKey}');
-      if (event.logicalKey == LogicalKeyboardKey.keyR) {
-        debugPrint('Changing color to red.');
-        setState(() {
-          _color = Colors.red;
-        });
-        return KeyEventResult.handled;
-      } else if (event.logicalKey == LogicalKeyboardKey.keyG) {
-        debugPrint('Changing color to green.');
-        setState(() {
-          _color = Colors.green;
-        });
-        return KeyEventResult.handled;
-      } else if (event.logicalKey == LogicalKeyboardKey.keyB) {
-        debugPrint('Changing color to blue.');
-        setState(() {
-          _color = Colors.blue;
-        });
-        return KeyEventResult.handled;
+      switch (event.logicalKey) {
+        case LogicalKeyboardKey.keyR:
+          debugPrint('Changing color to red.');
+          setState(() { _color = Colors.red; });
+          return KeyEventResult.handled;
+        case LogicalKeyboardKey.keyG:
+          debugPrint('Changing color to green.');
+          setState(() { _color = Colors.green; });
+          return KeyEventResult.handled;
+        case LogicalKeyboardKey.keyB:
+          debugPrint('Changing color to blue.');
+          setState(() { _color = Colors.blue; });
+          return KeyEventResult.handled;
       }
     }
     return KeyEventResult.ignored;

examples/api/lib/widgets/focus_scope/focus.0.dart

@@ -36,24 +36,19 @@ class _FocusExampleState extends State<FocusExample> {
   KeyEventResult _handleKeyPress(FocusNode node, KeyEvent event) {
     if (event is KeyDownEvent) {
       debugPrint('Focus node ${node.debugLabel} got key event: ${event.logicalKey}');
-      if (event.logicalKey == LogicalKeyboardKey.keyR) {
-        debugPrint('Changing color to red.');
-        setState(() {
-          _color = Colors.red;
-        });
-        return KeyEventResult.handled;
-      } else if (event.logicalKey == LogicalKeyboardKey.keyG) {
-        debugPrint('Changing color to green.');
-        setState(() {
-          _color = Colors.green;
-        });
-        return KeyEventResult.handled;
-      } else if (event.logicalKey == LogicalKeyboardKey.keyB) {
-        debugPrint('Changing color to blue.');
-        setState(() {
-          _color = Colors.blue;
-        });
-        return KeyEventResult.handled;
+      switch (event.logicalKey) {
+        case LogicalKeyboardKey.keyR:
+          debugPrint('Changing color to red.');
+          setState(() { _color = Colors.red; });
+          return KeyEventResult.handled;
+        case LogicalKeyboardKey.keyG:
+          debugPrint('Changing color to green.');
+          setState(() { _color = Colors.green; });
+          return KeyEventResult.handled;
+        case LogicalKeyboardKey.keyB:
+          debugPrint('Changing color to blue.');
+          setState(() { _color = Colors.blue; });
+          return KeyEventResult.handled;
       }
     }
     return KeyEventResult.ignored;

packages/flutter/lib/src/cupertino/list_section.dart

@@ -372,34 +372,31 @@ class CupertinoListSection extends StatelessWidget {
       height: dividerHeight,
     );
 
-    Widget? headerWidget;
-    if (header != null) {
-      headerWidget = DefaultTextStyle(
-        style: CupertinoTheme.of(context).textTheme.textStyle.merge(
-              type == CupertinoListSectionType.base
-                  ? TextStyle(
-                      fontSize: 13.0,
-                      color: CupertinoDynamicColor.resolve(
-                          _kHeaderFooterColor, context))
-                  : const TextStyle(
-                      fontSize: 20.0, fontWeight: FontWeight.bold),
-            ),
-        child: header!,
-      );
-    }
-
-    Widget? footerWidget;
-    if (footer != null) {
-      footerWidget = DefaultTextStyle(
-        style: type == CupertinoListSectionType.base
-            ? CupertinoTheme.of(context).textTheme.textStyle.merge(TextStyle(
-                  fontSize: 13.0,
-                  color: CupertinoDynamicColor.resolve(
-                      _kHeaderFooterColor, context),
-                ))
-            : CupertinoTheme.of(context).textTheme.textStyle,
-        child: footer!,
-      );
+    TextStyle style = CupertinoTheme.of(context).textTheme.textStyle;
+
+    Widget? headerWidget, footerWidget;
+    switch (type) {
+      case CupertinoListSectionType.base:
+        style = style.merge(TextStyle(
+          fontSize: 13.0,
+          color: CupertinoDynamicColor.resolve(_kHeaderFooterColor, context),
+        ));
+        if (header != null) {
+          headerWidget = DefaultTextStyle(style: style, child: header!);
+        }
+        if (footer != null) {
+          footerWidget = DefaultTextStyle(style: style, child: footer!);
+        }
+      case CupertinoListSectionType.insetGrouped:
+        if (header != null) {
+          headerWidget = DefaultTextStyle(
+            style: style.merge(const TextStyle(fontSize: 20.0, fontWeight: FontWeight.bold)),
+            child: header!,
+          );
+        }
+        if (footer != null) {
+          footerWidget = DefaultTextStyle(style: style, child: footer!);
+        }
     }
 
     Widget? decoratedChildrenGroup;

packages/flutter/lib/src/gestures/team.dart

@@ -73,16 +73,16 @@ class _CombiningGestureArenaMember extends GestureArenaMember {
     if (_resolved) {
       return;
     }
-    if (disposition == GestureDisposition.rejected) {
-      _members.remove(member);
-      member.rejectGesture(_pointer);
-      if (_members.isEmpty) {
+    switch (disposition) {
+      case GestureDisposition.accepted:
+        _winner ??= _owner.captain ?? member;
         _entry!.resolve(disposition);
-      }
-    } else {
-      assert(disposition == GestureDisposition.accepted);
-      _winner ??= _owner.captain ?? member;
-      _entry!.resolve(disposition);
+      case GestureDisposition.rejected:
+        _members.remove(member);
+        member.rejectGesture(_pointer);
+        if (_members.isEmpty) {
+          _entry!.resolve(disposition);
+        }
     }
   }
 }

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

@@ -2754,25 +2754,20 @@ class _HighlightPainter extends CustomPainter {
       ..color = color
       ..style = PaintingStyle.fill;
 
-    final Rect rectLeft = Rect.fromLTWH(0, 0, size.width / 2, size.height);
-    final Rect rectRight = Rect.fromLTWH(size.width / 2, 0, size.width / 2, size.height);
+    final bool rtl = switch (textDirection) {
+      TextDirection.rtl || null => true,
+      TextDirection.ltr => false,
+    };
 
     switch (style) {
-      case _HighlightPainterStyle.highlightTrailing:
-        canvas.drawRect(
-          textDirection == TextDirection.ltr ? rectRight : rectLeft,
-          paint,
-        );
+      case _HighlightPainterStyle.highlightLeading when rtl:
+      case _HighlightPainterStyle.highlightTrailing when !rtl:
+        canvas.drawRect(Rect.fromLTWH(size.width / 2, 0, size.width / 2, size.height), paint);
       case _HighlightPainterStyle.highlightLeading:
-        canvas.drawRect(
-          textDirection == TextDirection.ltr ? rectLeft : rectRight,
-          paint,
-        );
+      case _HighlightPainterStyle.highlightTrailing:
+        canvas.drawRect(Rect.fromLTWH(0, 0, size.width / 2, size.height), paint);
       case _HighlightPainterStyle.highlightAll:
-        canvas.drawRect(
-          Rect.fromLTWH(0, 0, size.width, size.height),
-          paint,
-        );
+        canvas.drawRect(Rect.fromLTWH(0, 0, size.width, size.height), paint);
       case _HighlightPainterStyle.none:
         break;
     }

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

@@ -1281,17 +1281,13 @@ class _CurvedAnimationBuilderState extends State<_CurvedAnimationBuilder> {
         _animationDirection = status;
       });
     }
-
-    if (status == AnimationStatus.completed || status == AnimationStatus.dismissed) {
-      setState(() {
-        _preservedDirection = null;
-      });
-    }
-
-    if (_preservedDirection == null && (status == AnimationStatus.forward || status == AnimationStatus.reverse)) {
-      setState(() {
-        _preservedDirection = status;
-      });
+    switch (status) {
+      case AnimationStatus.forward || AnimationStatus.reverse when _preservedDirection != null:
+        break;
+      case AnimationStatus.forward || AnimationStatus.reverse:
+        setState(() { _preservedDirection = status; });
+      case AnimationStatus.completed || AnimationStatus.dismissed:
+        setState(() { _preservedDirection = null; });
     }
   }
 

packages/flutter/test/cupertino/nav_bar_transition_test.dart

@@ -59,26 +59,24 @@ Future<void> startTransitionBetween(
 }
 
 CupertinoPageScaffold? scaffoldForNavBar(Widget? navBar) {
-  if (navBar is CupertinoNavigationBar || navBar == null) {
-    return CupertinoPageScaffold(
-      navigationBar: navBar as CupertinoNavigationBar? ?? const CupertinoNavigationBar(),
-      child: const Placeholder(),
-    );
-  } else if (navBar is CupertinoSliverNavigationBar) {
-    return CupertinoPageScaffold(
-      child: CustomScrollView(
-        slivers: <Widget>[
+  switch (navBar) {
+    case CupertinoNavigationBar? _:
+      return CupertinoPageScaffold(
+        navigationBar: navBar ?? const CupertinoNavigationBar(),
+        child: const Placeholder(),
+      );
+    case CupertinoSliverNavigationBar():
+      return CupertinoPageScaffold(
+        child: CustomScrollView(slivers: <Widget>[
           navBar,
           // Add filler so it's scrollable.
-          const SliverToBoxAdapter(
-            child: Placeholder(fallbackHeight: 1000.0),
-          ),
-        ],
-      ),
-    );
+          const SliverToBoxAdapter(child: Placeholder(fallbackHeight: 1000.0)),
+        ]),
+      );
+    default:
+      assert(false, 'Unexpected nav bar type ${navBar.runtimeType}');
+      return null;
   }
-  assert(false, 'Unexpected nav bar type ${navBar.runtimeType}');
-  return null;
 }
 
 Finder flying(WidgetTester tester, Finder finder) {

packages/flutter/test/widgets/scrollbar_test.dart

@@ -240,17 +240,13 @@ void main() {
           painter.paint(testCanvas, size);
           final Rect rect = captureRect();
 
-          switch (direction) {
-            case AxisDirection.up:
-            case AxisDirection.down:
-              expect(
-                margin,
-                textDirection == TextDirection.ltr
-                  ? size.width - rect.right
-                  : rect.left,
-              );
-            case AxisDirection.left:
-            case AxisDirection.right:
+          switch (axisDirectionToAxis(direction)) {
+            case Axis.vertical:
+              expect(margin, switch (textDirection) {
+                TextDirection.ltr => size.width - rect.right,
+                TextDirection.rtl => rect.left,
+              });
+            case Axis.horizontal:
               expect(margin, size.height - rect.bottom);
           }
         }

packages/flutter_test/lib/src/mock_canvas.dart

@@ -520,24 +520,19 @@ class _MismatchedCall extends Error {
 }
 
 bool _evaluatePainter(Object? object, Canvas canvas, PaintingContext context) {
-  if (object is _ContextPainterFunction) {
-    final _ContextPainterFunction function = object;
-    function(context, Offset.zero);
-  } else if (object is _CanvasPainterFunction) {
-    final _CanvasPainterFunction function = object;
-    function(canvas);
-  } else {
-    if (object is Finder) {
+  switch (object) {
+    case final _ContextPainterFunction function:
+      function(context, Offset.zero);
+    case final _CanvasPainterFunction function:
+      function(canvas);
+    case final Finder finder:
       TestAsyncUtils.guardSync();
-      final Finder finder = object;
-      object = finder.evaluate().single.renderObject;
-    }
-    if (object is RenderObject) {
-      final RenderObject renderObject = object;
+      final RenderObject? result = finder.evaluate().single.renderObject;
+      return (result?..paint(context, Offset.zero)) != null;
+    case final RenderObject renderObject:
       renderObject.paint(context, Offset.zero);
-    } else {
+    default:
       return false;
-    }
   }
   return true;
 }

packages/flutter_tools/lib/src/compile.dart

@@ -133,22 +133,20 @@ class StdoutHandler {
       compilerOutput?.complete(output);
       return;
     }
-    if (state == StdoutState.CollectDiagnostic) {
-      if (!_suppressCompilerMessages) {
-        _logger.printError(message);
-      } else {
+    switch (state) {
+      case StdoutState.CollectDiagnostic when _suppressCompilerMessages:
         _logger.printTrace(message);
-      }
-    } else {
-      assert(state == StdoutState.CollectDependencies);
-      switch (message[0]) {
-        case '+':
-          sources.add(Uri.parse(message.substring(1)));
-        case '-':
-          sources.remove(Uri.parse(message.substring(1)));
-        default:
-          _logger.printTrace('Unexpected prefix for $message uri - ignoring');
-      }
+      case StdoutState.CollectDiagnostic:
+        _logger.printError(message);
+      case StdoutState.CollectDependencies:
+        switch (message[0]) {
+          case '+':
+            sources.add(Uri.parse(message.substring(1)));
+          case '-':
+            sources.remove(Uri.parse(message.substring(1)));
+          default:
+            _logger.printTrace('Unexpected prefix for $message uri - ignoring');
+        }
     }
   }
 

packages/flutter_tools/lib/src/daemon.dart

@@ -101,19 +101,18 @@ class DaemonInputStreamConverter {
 
     int start = 0;
     while (start < chunk.length) {
-      if (state == _InputStreamParseState.json) {
-        start += _processChunkInJsonMode(chunk, start);
-      } else if (state == _InputStreamParseState.binary) {
-        final int bytesSent = _addBinaryChunk(chunk, start, remainingBinaryLength);
-        start += bytesSent;
-        remainingBinaryLength -= bytesSent;
-
-        if (remainingBinaryLength <= 0) {
-          assert(remainingBinaryLength == 0);
-
-          unawaited(currentBinaryStream.close());
-          state = _InputStreamParseState.json;
-        }
+      switch (state) {
+        case _InputStreamParseState.json:
+          start += _processChunkInJsonMode(chunk, start);
+        case _InputStreamParseState.binary:
+          final int bytesSent = _addBinaryChunk(chunk, start, remainingBinaryLength);
+          start += bytesSent;
+          remainingBinaryLength -= bytesSent;
+          if (remainingBinaryLength <= 0) {
+            assert(remainingBinaryLength == 0);
+            unawaited(currentBinaryStream.close());
+            state = _InputStreamParseState.json;
+          }
       }
     }
   }