Hook up soft keyboard "next" and "previous" buttons so that they move the focus by default (#63592)

Focus will be moved automatically if onEditingComplete is not specified, but must
by moved manually if onEditingComplete is specified.

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

@@ -1629,18 +1629,25 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
         // action; The newline is already inserted. Otherwise, finalize
         // editing.
         if (!_isMultiline)
-          _finalizeEditing(true);
+          _finalizeEditing(action, shouldUnfocus: true);
         break;
       case TextInputAction.done:
       case TextInputAction.go:
-      case TextInputAction.send:
+      case TextInputAction.next:
+      case TextInputAction.previous:
       case TextInputAction.search:
-        _finalizeEditing(true);
+      case TextInputAction.send:
+        _finalizeEditing(action, shouldUnfocus: true);
         break;
-      default:
+      case TextInputAction.continueAction:
+      case TextInputAction.emergencyCall:
+      case TextInputAction.join:
+      case TextInputAction.none:
+      case TextInputAction.route:
+      case TextInputAction.unspecified:
         // Finalize editing, but don't give up focus because this keyboard
         // action does not imply the user is done inputting information.
-        _finalizeEditing(false);
+        _finalizeEditing(action, shouldUnfocus: false);
         break;
     }
   }
@@ -1725,16 +1732,38 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
     }
   }
 
-  void _finalizeEditing(bool shouldUnfocus) {
+  void _finalizeEditing(TextInputAction action, {@required bool shouldUnfocus}) {
     // Take any actions necessary now that the user has completed editing.
     if (widget.onEditingComplete != null) {
       widget.onEditingComplete();
     } else {
       // Default behavior if the developer did not provide an
-      // onEditingComplete callback: Finalize editing and remove focus.
+      // onEditingComplete callback: Finalize editing and remove focus, or move
+      // it to the next/previous field, depending on the action.
       widget.controller.clearComposing();
-      if (shouldUnfocus)
-        widget.focusNode.unfocus();
+      if (shouldUnfocus) {
+        switch (action) {
+          case TextInputAction.none:
+          case TextInputAction.unspecified:
+          case TextInputAction.done:
+          case TextInputAction.go:
+          case TextInputAction.search:
+          case TextInputAction.send:
+          case TextInputAction.continueAction:
+          case TextInputAction.join:
+          case TextInputAction.route:
+          case TextInputAction.emergencyCall:
+          case TextInputAction.newline:
+            widget.focusNode.unfocus();
+            break;
+          case TextInputAction.next:
+            widget.focusNode.nextFocus();
+            break;
+          case TextInputAction.previous:
+            widget.focusNode.previousFocus();
+            break;
+        }
+      }
     }
 
     // Invoke optional callback with the user's submitted content.
@@ -1883,7 +1912,7 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
       _textInputConnection = null;
       _lastFormattedUnmodifiedTextEditingValue = null;
       _receivedRemoteTextEditingValue = null;
-      _finalizeEditing(true);
+      _finalizeEditing(TextInputAction.done, shouldUnfocus: true);
     }
   }
 

packages/flutter/test/widgets/editable_text_test.dart

@@ -1336,35 +1336,88 @@ void main() {
     expect(changedValue, clipboardContent);
   });
 
-  testWidgets('Does not lose focus by default when "next" action is pressed', (WidgetTester tester) async {
-    final FocusNode focusNode = FocusNode();
+  // The variants to test in the focus handling test.
+  final ValueVariant<TextInputAction> focusVariants = ValueVariant<
+      TextInputAction>(
+    TextInputAction.values.toSet(),
+  );
+
+  testWidgets('Handles focus correctly when action is invoked', (WidgetTester tester) async {
+    // The expectations for each of the types of TextInputAction.
+    const Map<TextInputAction, bool> actionShouldLoseFocus = <TextInputAction, bool>{
+      TextInputAction.none: false,
+      TextInputAction.unspecified: false,
+      TextInputAction.done: true,
+      TextInputAction.go: true,
+      TextInputAction.search: true,
+      TextInputAction.send: true,
+      TextInputAction.continueAction: false,
+      TextInputAction.join: false,
+      TextInputAction.route: false,
+      TextInputAction.emergencyCall: false,
+      TextInputAction.newline: true,
+      TextInputAction.next: true,
+      TextInputAction.previous: true,
+    };
+
+    final TextInputAction action = focusVariants.currentValue;
+    expect(actionShouldLoseFocus.containsKey(action), isTrue);
+
+    Future<void> _ensureCorrectFocusHandlingForAction(
+        TextInputAction action, {
+          @required bool shouldLoseFocus,
+          bool shouldFocusNext = false,
+          bool shouldFocusPrevious = false,
+        }) async {
+      final FocusNode focusNode = FocusNode();
+      final GlobalKey previousKey = GlobalKey();
+      final GlobalKey nextKey = GlobalKey();
 
-    final Widget widget = MaterialApp(
-      home: EditableText(
-        backgroundCursorColor: Colors.grey,
-        controller: TextEditingController(),
-        focusNode: focusNode,
-        style: Typography.material2018(platform: TargetPlatform.android).black.subtitle1,
-        cursorColor: Colors.blue,
-        selectionControls: materialTextSelectionControls,
-        keyboardType: TextInputType.text,
-      ),
-    );
-    await tester.pumpWidget(widget);
+      final Widget widget = MaterialApp(
+        home: Column(
+          children: <Widget>[
+            TextButton(
+                child: Text('Previous Widget', key: previousKey),
+                onPressed: () {}),
+            EditableText(
+              backgroundCursorColor: Colors.grey,
+              controller: TextEditingController(),
+              focusNode: focusNode,
+              style: Typography.material2018(platform: TargetPlatform.android).black.subtitle1,
+              cursorColor: Colors.blue,
+              selectionControls: materialTextSelectionControls,
+              keyboardType: TextInputType.text,
+              autofocus: true,
+            ),
+            TextButton(
+                child: Text('Next Widget', key: nextKey), onPressed: () {}),
+          ],
+        ),
+      );
+      await tester.pumpWidget(widget);
 
-    // Select EditableText to give it focus.
-    final Finder textFinder = find.byType(EditableText);
-    await tester.tap(textFinder);
-    await tester.pump();
+      assert(focusNode.hasFocus);
 
-    assert(focusNode.hasFocus);
+      await tester.testTextInput.receiveAction(action);
+      await tester.pump();
 
-    await tester.testTextInput.receiveAction(TextInputAction.next);
-    await tester.pump();
+      expect(Focus.of(nextKey.currentContext).hasFocus, equals(shouldFocusNext));
+      expect(Focus.of(previousKey.currentContext).hasFocus, equals(shouldFocusPrevious));
+      expect(focusNode.hasFocus, equals(!shouldLoseFocus));
+    }
 
-    // Still has focus after pressing "next".
-    expect(focusNode.hasFocus, true);
-  });
+    try {
+      await _ensureCorrectFocusHandlingForAction(
+        action,
+        shouldLoseFocus: actionShouldLoseFocus[action],
+        shouldFocusNext: action == TextInputAction.next,
+        shouldFocusPrevious: action == TextInputAction.previous,
+      );
+    } on PlatformException {
+      // on Android, continueAction isn't supported.
+      expect(action, equals(TextInputAction.continueAction));
+    }
+  }, variant: focusVariants);
 
   testWidgets('Does not lose focus by default when "done" action is pressed and onEditingComplete is provided', (WidgetTester tester) async {
     final FocusNode focusNode = FocusNode();

packages/flutter_test/lib/src/widget_tester.dart

@@ -271,6 +271,61 @@ class TargetPlatformVariant extends TestVariant<TargetPlatform> {
   }
 }
 
+/// A [TestVariant] that runs separate tests with each of the given values.
+///
+/// To use this variant, define it before the test, and then access
+/// [currentValue] inside the test.
+///
+/// The values are typically enums, but they don't have to be. The `toString`
+/// for the given value will be used to describe the variant. Values will have
+/// their type name stripped from their `toString` output, so that enum values
+/// will only print the value, not the type.
+///
+/// {@tool snippet}
+/// This example shows how to set up the test to access the [currentValue]. In
+/// this example, two tests will be run, one with `value1`, and one with
+/// `value2`. The test with `value2` will fail. The names of the tests will be:
+///
+///   - `Test handling of TestScenario (value1)`
+///   - `Test handling of TestScenario (value2)`
+///
+/// ```dart
+/// enum TestScenario {
+///   value1,
+///   value2,
+///   value3,
+/// }
+///
+/// final ValueVariant<TestScenario> variants = ValueVariant<TestScenario>(
+///   <TestScenario>{value1, value2},
+/// );
+///
+/// testWidgets('Test handling of TestScenario', (WidgetTester tester) {
+///   expect(variants.currentValue, equals(value1));
+/// }, variant: variants);
+/// ```
+/// {@end-tool}
+class ValueVariant<T> extends TestVariant<T> {
+  /// Creates a [ValueVariant] that tests the given [values].
+  ValueVariant(this.values);
+
+  /// Returns the value currently under test.
+  T get currentValue => _currentValue;
+  T _currentValue;
+
+  @override
+  final Set<T> values;
+
+  @override
+  String describeValue(T value) => value.toString().replaceFirst('$T.', '');
+
+  @override
+  Future<T> setUp(T value) async => _currentValue = value;
+
+  @override
+  Future<void> tearDown(T value, T memento) async {}
+}
+
 /// The warning message to show when a benchmark is performed with assert on.
 const String kDebugWarning = '''
 ┏╍╍╍╍╍╍╍╍╍╍╍╍╍╍╍╍╍╍╍╍╍╍╍╍╍╍╍╍╍╍╍╍╍╍╍╍╍╍╍╍╍╍╍╍╍╍╍╍╍╍╍╍╍╍╍┓