Reverts default DragStartBehavior to DragStartBehavior.down (#26734)

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

@@ -59,7 +59,7 @@ class CupertinoSwitch extends StatefulWidget {
     @required this.value,
     @required this.onChanged,
     this.activeColor,
-    this.dragStartBehavior = DragStartBehavior.start,
+    this.dragStartBehavior = DragStartBehavior.down,
   }) : assert(dragStartBehavior != null),
        super(key: key);
 
@@ -96,6 +96,7 @@ class CupertinoSwitch extends StatefulWidget {
   /// [CupertinoTheme] in accordance to native iOS behavior.
   final Color activeColor;
 
+  // TODO(jslavitz): Set the DragStartBehavior default to be start across all widgets.
   /// {@template flutter.cupertino.switch.dragStartBehavior}
   /// Determines the way that drag start behavior is handled.
   ///
@@ -108,7 +109,7 @@ class CupertinoSwitch extends StatefulWidget {
   /// animation smoother and setting it to [DragStartBehavior.down] will make
   /// drag behavior feel slightly more reactive.
   ///
-  /// By default, the drag start behavior is [DragStartBehavior.start].
+  /// By default, the drag start behavior is [DragStartBehavior.down].
   ///
   /// See also:
   ///
@@ -147,7 +148,7 @@ class _CupertinoSwitchRenderObjectWidget extends LeafRenderObjectWidget {
     this.activeColor,
     this.onChanged,
     this.vsync,
-    this.dragStartBehavior = DragStartBehavior.start,
+    this.dragStartBehavior = DragStartBehavior.down,
   }) : super(key: key);
 
   final bool value;
@@ -200,7 +201,7 @@ class _RenderCupertinoSwitch extends RenderConstrainedBox {
     ValueChanged<bool> onChanged,
     @required TextDirection textDirection,
     @required TickerProvider vsync,
-    DragStartBehavior dragStartBehavior = DragStartBehavior.start,
+    DragStartBehavior dragStartBehavior = DragStartBehavior.down,
   }) : assert(value != null),
        assert(activeColor != null),
        assert(vsync != null),

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

@@ -54,7 +54,7 @@ abstract class DragGestureRecognizer extends OneSequenceGestureRecognizer {
   /// [dragStartBehavior] must not be null.
   DragGestureRecognizer({
     Object debugOwner,
-    this.dragStartBehavior = DragStartBehavior.start,
+    this.dragStartBehavior = DragStartBehavior.down,
   }) : assert(dragStartBehavior != null),
        super(debugOwner: debugOwner);
 

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

@@ -251,7 +251,7 @@ class DayPicker extends StatelessWidget {
     @required this.lastDate,
     @required this.displayedMonth,
     this.selectableDayPredicate,
-    this.dragStartBehavior = DragStartBehavior.start,
+    this.dragStartBehavior = DragStartBehavior.down,
   }) : assert(selectedDate != null),
        assert(currentDate != null),
        assert(onChanged != null),
@@ -284,6 +284,7 @@ class DayPicker extends StatelessWidget {
   /// Optional user supplied predicate function to customize selectable days.
   final SelectableDayPredicate selectableDayPredicate;
 
+  // TODO(jslavitz): Set the DragStartBehavior default to be start across all widgets.
   /// Determines the way that drag start behavior is handled.
   ///
   /// If set to [DragStartBehavior.start], the drag gesture used to scroll a
@@ -295,7 +296,7 @@ class DayPicker extends StatelessWidget {
   /// animation smoother and setting it to [DragStartBehavior.down] will make
   /// drag behavior feel slightly more reactive.
   ///
-  /// By default, the drag start behavior is [DragStartBehavior.start].
+  /// By default, the drag start behavior is [DragStartBehavior.down].
   ///
   /// See also:
   ///
@@ -524,7 +525,7 @@ class MonthPicker extends StatefulWidget {
     @required this.firstDate,
     @required this.lastDate,
     this.selectableDayPredicate,
-    this.dragStartBehavior = DragStartBehavior.start,
+    this.dragStartBehavior = DragStartBehavior.down,
   }) : assert(selectedDate != null),
        assert(onChanged != null),
        assert(!firstDate.isAfter(lastDate)),
@@ -787,7 +788,7 @@ class YearPicker extends StatefulWidget {
     @required this.onChanged,
     @required this.firstDate,
     @required this.lastDate,
-    this.dragStartBehavior = DragStartBehavior.start,
+    this.dragStartBehavior = DragStartBehavior.down,
   }) : assert(selectedDate != null),
        assert(onChanged != null),
        assert(!firstDate.isAfter(lastDate)),

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

@@ -180,7 +180,7 @@ class DrawerController extends StatefulWidget {
     @required this.child,
     @required this.alignment,
     this.drawerCallback,
-    this.dragStartBehavior = DragStartBehavior.start,
+    this.dragStartBehavior = DragStartBehavior.down,
   }) : assert(child != null),
        assert(dragStartBehavior != null),
        assert(alignment != null),
@@ -200,6 +200,7 @@ class DrawerController extends StatefulWidget {
   /// Optional callback that is called when a [Drawer] is opened or closed.
   final DrawerCallback drawerCallback;
 
+  // TODO(jslavitz): Set the DragStartBehavior default to be start across all widgets.
   /// {@template flutter.material.drawer.dragStartBehavior}
   /// Determines the way that drag start behavior is handled.
   ///
@@ -212,7 +213,7 @@ class DrawerController extends StatefulWidget {
   /// animation smoother and setting it to [DragStartBehavior.down] will make
   /// drag behavior feel slightly more reactive.
   ///
-  /// By default, the drag start behavior is [DragStartBehavior.start].
+  /// By default, the drag start behavior is [DragStartBehavior.down].
   ///
   /// See also:
   ///

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

@@ -75,7 +75,7 @@ class PaginatedDataTable extends StatefulWidget {
     this.rowsPerPage = defaultRowsPerPage,
     this.availableRowsPerPage = const <int>[defaultRowsPerPage, defaultRowsPerPage * 2, defaultRowsPerPage * 5, defaultRowsPerPage * 10],
     this.onRowsPerPageChanged,
-    this.dragStartBehavior = DragStartBehavior.start,
+    this.dragStartBehavior = DragStartBehavior.down,
     @required this.source
   }) : assert(header != null),
        assert(columns != null),

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

@@ -796,7 +796,7 @@ class Scaffold extends StatefulWidget {
     this.resizeToAvoidBottomPadding,
     this.resizeToAvoidBottomInset,
     this.primary = true,
-    this.drawerDragStartBehavior = DragStartBehavior.start,
+    this.drawerDragStartBehavior = DragStartBehavior.down,
   }) : assert(primary != null),
        assert(drawerDragStartBehavior != null),
        super(key: key);

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

@@ -551,7 +551,7 @@ class TabBar extends StatefulWidget implements PreferredSizeWidget {
     this.labelPadding,
     this.unselectedLabelColor,
     this.unselectedLabelStyle,
-    this.dragStartBehavior = DragStartBehavior.start,
+    this.dragStartBehavior = DragStartBehavior.down,
     this.onTap,
   }) : assert(tabs != null),
        assert(isScrollable != null),
@@ -1043,7 +1043,7 @@ class TabBarView extends StatefulWidget {
     @required this.children,
     this.controller,
     this.physics,
-    this.dragStartBehavior = DragStartBehavior.start,
+    this.dragStartBehavior = DragStartBehavior.down,
   }) : assert(children != null),
        assert(dragStartBehavior != null),
        super(key: key);

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

@@ -143,7 +143,7 @@ class TextField extends StatefulWidget {
     this.cursorColor,
     this.keyboardAppearance,
     this.scrollPadding = const EdgeInsets.all(20.0),
-    this.dragStartBehavior = DragStartBehavior.start,
+    this.dragStartBehavior = DragStartBehavior.down,
     this.enableInteractiveSelection,
     this.onTap,
     this.buildCounter,

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

@@ -84,7 +84,7 @@ class Dismissible extends StatefulWidget {
     this.dismissThresholds = const <DismissDirection, double>{},
     this.movementDuration = const Duration(milliseconds: 200),
     this.crossAxisEndOffset = 0.0,
-    this.dragStartBehavior = DragStartBehavior.start,
+    this.dragStartBehavior = DragStartBehavior.down,
   }) : assert(key != null),
        assert(secondaryBackground != null ? background != null : true),
        assert(dragStartBehavior != null),
@@ -146,6 +146,7 @@ class Dismissible extends StatefulWidget {
   /// it is positive or negative.
   final double crossAxisEndOffset;
 
+  // TODO(jslavitz): Set the DragStartBehavior default to be start across all widgets.
   /// Determines the way that drag start behavior is handled.
   ///
   /// If set to [DragStartBehavior.start], the drag gesture used to dismiss a
@@ -156,7 +157,7 @@ class Dismissible extends StatefulWidget {
   /// animation smoother and setting it to [DragStartBehavior.down] will make
   /// drag behavior feel slightly more reactive.
   ///
-  /// By default, the drag start behavior is [DragStartBehavior.start].
+  /// By default, the drag start behavior is [DragStartBehavior.down].
   ///
   /// See also:
   ///

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

@@ -217,7 +217,7 @@ class EditableText extends StatefulWidget {
     this.cursorRadius,
     this.scrollPadding = const EdgeInsets.all(20.0),
     this.keyboardAppearance = Brightness.light,
-    this.dragStartBehavior = DragStartBehavior.start,
+    this.dragStartBehavior = DragStartBehavior.down,
     this.enableInteractiveSelection,
   }) : assert(controller != null),
        assert(focusNode != null),

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

@@ -186,7 +186,7 @@ class GestureDetector extends StatelessWidget {
     this.onScaleEnd,
     this.behavior,
     this.excludeFromSemantics = false,
-    this.dragStartBehavior = DragStartBehavior.start,
+    this.dragStartBehavior = DragStartBehavior.down,
   }) : assert(excludeFromSemantics != null),
        assert(dragStartBehavior != null),
        assert(() {
@@ -373,6 +373,7 @@ class GestureDetector extends StatelessWidget {
   /// duplication of information.
   final bool excludeFromSemantics;
 
+  // TODO(jslavitz): Set the DragStartBehavior default to be start across all widgets.
   /// Determines the way that drag start behavior is handled.
   ///
   /// If set to [DragStartBehavior.start], gesture drag behavior will
@@ -383,7 +384,7 @@ class GestureDetector extends StatelessWidget {
   /// animation smoother and setting it to [DragStartBehavior.down] will make
   /// drag behavior feel slightly more reactive.
   ///
-  /// By default, the drag start behavior is [DragStartBehavior.start].
+  /// By default, the drag start behavior is [DragStartBehavior.down].
   ///
   /// Only the [onStart] callbacks for the [VerticalDragGestureRecognizer],
   /// [HorizontalDragGestureRecognizer] and [PanGestureRecognizer] are affected

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

@@ -189,7 +189,7 @@ class NestedScrollView extends StatefulWidget {
     this.physics,
     @required this.headerSliverBuilder,
     @required this.body,
-    this.dragStartBehavior = DragStartBehavior.start,
+    this.dragStartBehavior = DragStartBehavior.down,
   }) : assert(scrollDirection != null),
        assert(reverse != null),
        assert(headerSliverBuilder != null),
@@ -371,7 +371,7 @@ class _NestedScrollViewCustomScrollView extends CustomScrollView {
     @required ScrollController controller,
     @required List<Widget> slivers,
     @required this.handle,
-    DragStartBehavior dragStartBehavior = DragStartBehavior.start,
+    DragStartBehavior dragStartBehavior = DragStartBehavior.down,
   }) : super(
          scrollDirection: scrollDirection,
          reverse: reverse,

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

@@ -424,7 +424,7 @@ class PageView extends StatefulWidget {
     this.pageSnapping = true,
     this.onPageChanged,
     List<Widget> children = const <Widget>[],
-    this.dragStartBehavior = DragStartBehavior.start,
+    this.dragStartBehavior = DragStartBehavior.down,
   }) : controller = controller ?? _defaultPageController,
        childrenDelegate = SliverChildListDelegate(children),
        super(key: key);
@@ -451,7 +451,7 @@ class PageView extends StatefulWidget {
     this.onPageChanged,
     @required IndexedWidgetBuilder itemBuilder,
     int itemCount,
-    this.dragStartBehavior = DragStartBehavior.start,
+    this.dragStartBehavior = DragStartBehavior.down,
   }) : controller = controller ?? _defaultPageController,
        childrenDelegate = SliverChildBuilderDelegate(itemBuilder, childCount: itemCount),
        super(key: key);
@@ -467,7 +467,7 @@ class PageView extends StatefulWidget {
     this.pageSnapping = true,
     this.onPageChanged,
     @required this.childrenDelegate,
-    this.dragStartBehavior = DragStartBehavior.start,
+    this.dragStartBehavior = DragStartBehavior.down,
   }) : assert(childrenDelegate != null),
        controller = controller ?? _defaultPageController,
        super(key: key);

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

@@ -61,7 +61,7 @@ abstract class ScrollView extends StatelessWidget {
     this.shrinkWrap = false,
     this.cacheExtent,
     this.semanticChildCount,
-    this.dragStartBehavior = DragStartBehavior.start,
+    this.dragStartBehavior = DragStartBehavior.down,
   }) : assert(reverse != null),
        assert(shrinkWrap != null),
        assert(dragStartBehavior != null),
@@ -404,7 +404,7 @@ class CustomScrollView extends ScrollView {
     double cacheExtent,
     this.slivers = const <Widget>[],
     int semanticChildCount,
-    DragStartBehavior dragStartBehavior = DragStartBehavior.start,
+    DragStartBehavior dragStartBehavior = DragStartBehavior.down,
   }) : super(
     key: key,
     scrollDirection: scrollDirection,
@@ -448,7 +448,7 @@ abstract class BoxScrollView extends ScrollView {
     this.padding,
     double cacheExtent,
     int semanticChildCount,
-    DragStartBehavior dragStartBehavior = DragStartBehavior.start,
+    DragStartBehavior dragStartBehavior = DragStartBehavior.down,
   }) : super(
     key: key,
     scrollDirection: scrollDirection,
@@ -750,7 +750,7 @@ class ListView extends BoxScrollView {
     double cacheExtent,
     List<Widget> children = const <Widget>[],
     int semanticChildCount,
-    DragStartBehavior dragStartBehavior = DragStartBehavior.start,
+    DragStartBehavior dragStartBehavior = DragStartBehavior.down,
   }) : childrenDelegate = SliverChildListDelegate(
          children,
          addAutomaticKeepAlives: addAutomaticKeepAlives,
@@ -813,7 +813,7 @@ class ListView extends BoxScrollView {
     bool addSemanticIndexes = true,
     double cacheExtent,
     int semanticChildCount,
-    DragStartBehavior dragStartBehavior = DragStartBehavior.start,
+    DragStartBehavior dragStartBehavior = DragStartBehavior.down,
   }) : childrenDelegate = SliverChildBuilderDelegate(
          itemBuilder,
          childCount: itemCount,
@@ -1265,7 +1265,7 @@ class GridView extends BoxScrollView {
     @required this.childrenDelegate,
     double cacheExtent,
     int semanticChildCount,
-    DragStartBehavior dragStartBehavior = DragStartBehavior.start,
+    DragStartBehavior dragStartBehavior = DragStartBehavior.down,
   }) : assert(gridDelegate != null),
        assert(childrenDelegate != null),
        super(
@@ -1315,7 +1315,7 @@ class GridView extends BoxScrollView {
     double cacheExtent,
     List<Widget> children = const <Widget>[],
     int semanticChildCount,
-    DragStartBehavior dragStartBehavior = DragStartBehavior.start,
+    DragStartBehavior dragStartBehavior = DragStartBehavior.down,
   }) : gridDelegate = SliverGridDelegateWithFixedCrossAxisCount(
          crossAxisCount: crossAxisCount,
          mainAxisSpacing: mainAxisSpacing,
@@ -1373,7 +1373,7 @@ class GridView extends BoxScrollView {
     bool addSemanticIndexes = true,
     List<Widget> children = const <Widget>[],
     int semanticChildCount,
-    DragStartBehavior dragStartBehavior = DragStartBehavior.start,
+    DragStartBehavior dragStartBehavior = DragStartBehavior.down,
   }) : gridDelegate = SliverGridDelegateWithMaxCrossAxisExtent(
          maxCrossAxisExtent: maxCrossAxisExtent,
          mainAxisSpacing: mainAxisSpacing,

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

@@ -81,7 +81,7 @@ class Scrollable extends StatefulWidget {
     @required this.viewportBuilder,
     this.excludeFromSemantics = false,
     this.semanticChildCount,
-    this.dragStartBehavior = DragStartBehavior.start,
+    this.dragStartBehavior = DragStartBehavior.down,
   }) : assert(axisDirection != null),
        assert(dragStartBehavior != null),
        assert(viewportBuilder != null),
@@ -182,6 +182,7 @@ class Scrollable extends StatefulWidget {
   ///  * [SemanticsConfiguration.scrollChildCount], the corresponding semantics property.
   final int semanticChildCount;
 
+  // TODO(jslavitz): Set the DragStartBehavior default to be start across all widgets.
   /// {@template flutter.widgets.scrollable.dragStartBehavior}
   /// Determines the way that drag start behavior is handled.
   ///
@@ -193,7 +194,7 @@ class Scrollable extends StatefulWidget {
   /// animation smoother and setting it to [DragStartBehavior.down] will make
   /// drag behavior feel slightly more reactive.
   ///
-  /// By default, the drag start behavior is [DragStartBehavior.start].
+  /// By default, the drag start behavior is [DragStartBehavior.down].
   ///
   /// See also:
   ///

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

@@ -193,7 +193,7 @@ class SingleChildScrollView extends StatelessWidget {
     this.physics,
     this.controller,
     this.child,
-    this.dragStartBehavior = DragStartBehavior.start,
+    this.dragStartBehavior = DragStartBehavior.down,
   }) : assert(scrollDirection != null),
        assert(dragStartBehavior != null),
        assert(!(controller != null && primary == true),

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

@@ -230,7 +230,7 @@ class TextSelectionOverlay {
     @required this.renderObject,
     this.selectionControls,
     this.selectionDelegate,
-    this.dragStartBehavior = DragStartBehavior.start,
+    this.dragStartBehavior = DragStartBehavior.down,
   }): assert(value != null),
       assert(context != null),
       _value = value {
@@ -265,6 +265,7 @@ class TextSelectionOverlay {
   /// text field.
   final TextSelectionDelegate selectionDelegate;
 
+  // TODO(jslavitz): Set the DragStartBehavior default to be start across all widgets.
   /// Determines the way that drag start behavior is handled.
   ///
   /// If set to [DragStartBehavior.start], handle drag behavior will
@@ -275,7 +276,7 @@ class TextSelectionOverlay {
   /// animation smoother and setting it to [DragStartBehavior.down] will make
   /// drag behavior feel slightly more reactive.
   ///
-  /// By default, the drag start behavior is [DragStartBehavior.start].
+  /// By default, the drag start behavior is [DragStartBehavior.down].
   ///
   /// See also:
   ///
@@ -467,7 +468,7 @@ class _TextSelectionHandleOverlay extends StatefulWidget {
     @required this.onSelectionHandleChanged,
     @required this.onSelectionHandleTapped,
     @required this.selectionControls,
-    this.dragStartBehavior = DragStartBehavior.start,
+    this.dragStartBehavior = DragStartBehavior.down,
   }) : super(key: key);
 
   final TextSelection selection;

packages/flutter/test/gestures/drag_test.dart

@@ -58,7 +58,9 @@ void main() {
     tester.route(pointer.move(const Offset(20.0, 30.0))); // moved 10 horizontally and 20 vertically which is 22 total
     expect(didStartPan, isTrue); // 22 > 18
     didStartPan = false;
-    expect(updatedScrollDelta, null);
+    // TODO(jslavitz): revert this testing change.
+    expect(updatedScrollDelta, const Offset(10.0, 20.0));
+    updatedScrollDelta = null;
     expect(didEndPan, isFalse);
     expect(didTap, isFalse);
 
@@ -164,57 +166,7 @@ void main() {
     drag.dispose();
   });
 
-  testGesture('Should report most recent point to onStart by default', (GestureTester tester) {
-    final HorizontalDragGestureRecognizer drag = HorizontalDragGestureRecognizer();
-    final VerticalDragGestureRecognizer competingDrag = VerticalDragGestureRecognizer();
-
-    Offset positionAtOnStart;
-    drag.onStart = (DragStartDetails details) {
-      positionAtOnStart = details.globalPosition;
-    };
-
-    final TestPointer pointer = TestPointer(5);
-    final PointerDownEvent down = pointer.down(const Offset(10.0, 10.0));
-    drag.addPointer(down);
-    competingDrag.addPointer(down);
-    tester.closeArena(5);
-    tester.route(down);
-
-    tester.route(pointer.move(const Offset(30.0, 0.0)));
-    drag.dispose();
-    competingDrag.dispose();
-
-    expect(positionAtOnStart, const Offset(30.0, 00.0));
-  });
-
-  testGesture('Should report most recent point to onStart with a start configuration', (GestureTester tester) {
-    final HorizontalDragGestureRecognizer drag =
-    HorizontalDragGestureRecognizer();
-    final VerticalDragGestureRecognizer competingDrag = VerticalDragGestureRecognizer();
-
-    Offset positionAtOnStart;
-    drag.onStart = (DragStartDetails details) {
-      positionAtOnStart = details.globalPosition;
-    };
-    Offset updateOffset;
-    drag.onUpdate = (DragUpdateDetails details) {
-      updateOffset = details.globalPosition;
-    };
-
-    final TestPointer pointer = TestPointer(5);
-    final PointerDownEvent down = pointer.down(const Offset(10.0, 10.0));
-    drag.addPointer(down);
-    competingDrag.addPointer(down);
-    tester.closeArena(5);
-    tester.route(down);
-
-    tester.route(pointer.move(const Offset(30.0, 0.0)));
-    drag.dispose();
-    competingDrag.dispose();
-
-    expect(positionAtOnStart, const Offset(30.0, 0.0));
-    expect(updateOffset, null);
-  });
+  // TODO(jslavitz): Revert these tests.
 
   testGesture('Should report initial down point to onStart with a down configuration', (GestureTester tester) {
     final HorizontalDragGestureRecognizer drag =