Revert "Teach drag start behaviors to DragGestureRecognizer (flutter#23424)" (flutter#26209)

This reverts commit 08538f9.

Author: jslavitz

examples/flutter_gallery/lib/demo/material/drawer_demo.dart

@@ -3,7 +3,6 @@
 // found in the LICENSE file.
 
 import 'package:flutter/material.dart';
-import 'package:flutter/gestures.dart' show DragStartBehavior;
 
 import '../../gallery/demo.dart';
 
@@ -80,7 +79,6 @@ class _DrawerDemoState extends State<DrawerDemo> with TickerProviderStateMixin {
   @override
   Widget build(BuildContext context) {
     return Scaffold(
-      drawerDragStartBehavior: DragStartBehavior.down,
       key: _scaffoldKey,
       appBar: AppBar(
         leading: IconButton(
@@ -108,7 +106,6 @@ class _DrawerDemoState extends State<DrawerDemo> with TickerProviderStateMixin {
               ),
               otherAccountsPictures: <Widget>[
                 GestureDetector(
-                  dragStartBehavior: DragStartBehavior.down,
                   onTap: () {
                     _onOtherAccountsTap(context);
                   },
@@ -123,7 +120,6 @@ class _DrawerDemoState extends State<DrawerDemo> with TickerProviderStateMixin {
                   ),
                 ),
                 GestureDetector(
-                  dragStartBehavior: DragStartBehavior.down,
                   onTap: () {
                     _onOtherAccountsTap(context);
                   },
@@ -153,7 +149,6 @@ class _DrawerDemoState extends State<DrawerDemo> with TickerProviderStateMixin {
               removeTop: true,
               child: Expanded(
                 child: ListView(
-                  dragStartBehavior: DragStartBehavior.down,
                   padding: const EdgeInsets.only(top: 8.0),
                   children: <Widget>[
                     Stack(

examples/flutter_gallery/lib/demo/material/text_form_field_demo.dart

@@ -6,7 +6,6 @@ import 'dart:async';
 
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
-import 'package:flutter/gestures.dart' show DragStartBehavior;
 
 import '../../gallery/demo.dart';
 
@@ -68,7 +67,6 @@ class _PasswordFieldState extends State<PasswordField> {
         labelText: widget.labelText,
         helperText: widget.helperText,
         suffixIcon: GestureDetector(
-          dragStartBehavior: DragStartBehavior.down,
           onTap: () {
             setState(() {
               _obscureText = !_obscureText;
@@ -169,7 +167,6 @@ class TextFormFieldDemoState extends State<TextFormFieldDemo> {
   @override
   Widget build(BuildContext context) {
     return Scaffold(
-      drawerDragStartBehavior: DragStartBehavior.down,
       key: _scaffoldKey,
       appBar: AppBar(
         title: const Text('Text fields'),
@@ -183,7 +180,6 @@ class TextFormFieldDemoState extends State<TextFormFieldDemo> {
           autovalidate: _autovalidate,
           onWillPop: _warnUserAboutInvalidData,
           child: SingleChildScrollView(
-            dragStartBehavior: DragStartBehavior.down,
             padding: const EdgeInsets.symmetric(horizontal: 16.0),
             child: Column(
               crossAxisAlignment: CrossAxisAlignment.stretch,

examples/stocks/lib/stock_home.dart

@@ -5,7 +5,6 @@
 import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart' show debugDumpRenderTree, debugDumpLayerTree, debugDumpSemanticsTree, DebugSemanticsDumpOrder;
 import 'package:flutter/scheduler.dart' show timeDilation;
-import 'package:flutter/gestures.dart' show DragStartBehavior;
 import 'stock_data.dart';
 import 'stock_list.dart';
 import 'stock_strings.dart';
@@ -111,7 +110,6 @@ class StockHomeState extends State<StockHome> {
   Widget _buildDrawer(BuildContext context) {
     return Drawer(
       child: ListView(
-        dragStartBehavior: DragStartBehavior.down,
         children: <Widget>[
           const DrawerHeader(child: Center(child: Text('Stocks'))),
           const ListTile(
@@ -319,13 +317,11 @@ class StockHomeState extends State<StockHome> {
     return DefaultTabController(
       length: 2,
       child: Scaffold(
-        drawerDragStartBehavior: DragStartBehavior.down,
         key: _scaffoldKey,
         appBar: _isSearching ? buildSearchBar() : buildAppBar(),
         floatingActionButton: buildFloatingActionButton(),
         drawer: _buildDrawer(context),
         body: TabBarView(
-          dragStartBehavior: DragStartBehavior.down,
           children: <Widget>[
             _buildStockTab(context, StockHomeTab.market, widget.stocks.allSymbols),
             _buildStockTab(context, StockHomeTab.portfolio, portfolioSymbols),

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

@@ -52,16 +52,12 @@ import 'thumb_painter.dart';
 ///  * <https://developer.apple.com/ios/human-interface-guidelines/controls/switches/>
 class CupertinoSwitch extends StatefulWidget {
   /// Creates an iOS-style switch.
-  ///
-  /// [dragStartBehavior] must not be null.
   const CupertinoSwitch({
     Key key,
     @required this.value,
     @required this.onChanged,
     this.activeColor,
-    this.dragStartBehavior = DragStartBehavior.start,
-  }) : assert(dragStartBehavior != null),
-       super(key: key);
+  }) : super(key: key);
 
   /// Whether this switch is on or off.
   final bool value;
@@ -96,26 +92,6 @@ class CupertinoSwitch extends StatefulWidget {
   /// [CupertinoTheme] in accordance to native iOS behavior.
   final Color activeColor;
 
-  /// {@template flutter.cupertino.switch.dragStartBehavior}
-  /// Determines the way that drag start behavior is handled.
-  ///
-  /// If set to [DragStartBehavior.start], the drag behavior used to move the
-  /// switch from on to off will begin upon the detection of a drag gesture. If
-  /// set to [DragStartBehavior.down] it will begin when a down event is first
-  /// detected.
-  ///
-  /// In general, setting this to [DragStartBehavior.start] will make drag
-  /// 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].
-  ///
-  /// See also:
-  ///
-  ///  * [DragGestureRecognizer.dragStartBehavior], which gives an example for the different behaviors.
-  /// {@endtemplate}
-  final DragStartBehavior dragStartBehavior;
-
   @override
   _CupertinoSwitchState createState() => _CupertinoSwitchState();
 
@@ -135,7 +111,6 @@ class _CupertinoSwitchState extends State<CupertinoSwitch> with TickerProviderSt
       activeColor: widget.activeColor ?? CupertinoColors.activeGreen,
       onChanged: widget.onChanged,
       vsync: this,
-      dragStartBehavior: widget.dragStartBehavior,
     );
   }
 }
@@ -147,14 +122,12 @@ class _CupertinoSwitchRenderObjectWidget extends LeafRenderObjectWidget {
     this.activeColor,
     this.onChanged,
     this.vsync,
-    this.dragStartBehavior = DragStartBehavior.start,
   }) : super(key: key);
 
   final bool value;
   final Color activeColor;
   final ValueChanged<bool> onChanged;
   final TickerProvider vsync;
-  final DragStartBehavior dragStartBehavior;
 
   @override
   _RenderCupertinoSwitch createRenderObject(BuildContext context) {
@@ -164,7 +137,6 @@ class _CupertinoSwitchRenderObjectWidget extends LeafRenderObjectWidget {
       onChanged: onChanged,
       textDirection: Directionality.of(context),
       vsync: vsync,
-      dragStartBehavior: dragStartBehavior
     );
   }
 
@@ -175,8 +147,7 @@ class _CupertinoSwitchRenderObjectWidget extends LeafRenderObjectWidget {
       ..activeColor = activeColor
       ..onChanged = onChanged
       ..textDirection = Directionality.of(context)
-      ..vsync = vsync
-      ..dragStartBehavior = dragStartBehavior;
+      ..vsync = vsync;
   }
 }
 
@@ -200,7 +171,6 @@ class _RenderCupertinoSwitch extends RenderConstrainedBox {
     ValueChanged<bool> onChanged,
     @required TextDirection textDirection,
     @required TickerProvider vsync,
-    DragStartBehavior dragStartBehavior = DragStartBehavior.start,
   }) : assert(value != null),
        assert(activeColor != null),
        assert(vsync != null),
@@ -218,8 +188,7 @@ class _RenderCupertinoSwitch extends RenderConstrainedBox {
     _drag = HorizontalDragGestureRecognizer()
       ..onStart = _handleDragStart
       ..onUpdate = _handleDragUpdate
-      ..onEnd = _handleDragEnd
-      ..dragStartBehavior = dragStartBehavior;
+      ..onEnd = _handleDragEnd;
     _positionController = AnimationController(
       duration: _kToggleDuration,
       value: value ? 1.0 : 0.0,
@@ -307,14 +276,6 @@ class _RenderCupertinoSwitch extends RenderConstrainedBox {
     markNeedsPaint();
   }
 
-  DragStartBehavior get dragStartBehavior => _drag.dragStartBehavior;
-  set dragStartBehavior(DragStartBehavior value) {
-    assert(value != null);
-    if (_drag.dragStartBehavior == value)
-      return;
-    _drag.dragStartBehavior = value;
-  }
-
   bool get isInteractive => onChanged != null;
 
   TapGestureRecognizer _tap;

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

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'package:flutter/foundation.dart';
-
 import 'arena.dart';
 import 'constants.dart';
 import 'drag_details.dart';
@@ -50,36 +48,7 @@ typedef GestureDragCancelCallback = void Function();
 ///  * [PanGestureRecognizer], for drags that are not locked to a single axis.
 abstract class DragGestureRecognizer extends OneSequenceGestureRecognizer {
   /// Initialize the object.
-  ///
-  /// [dragStartBehavior] must not be null.
-  DragGestureRecognizer({
-    Object debugOwner,
-    this.dragStartBehavior = DragStartBehavior.start,
-  }) : assert(dragStartBehavior != null),
-       super(debugOwner: debugOwner);
-
-  /// Configure the behavior of offsets sent to [onStart].
-  ///
-  /// If set to [DragStartBehavior.start], the [onStart] callback will be called at the time and
-  /// position when the gesture detector wins the arena. If [DragStartBehavior.down],
-  /// [onStart] will be called at the time and position when a down event was
-  /// first detected.
-  ///
-  /// For more information about the gesture arena:
-  /// https://flutter.io/docs/development/ui/advanced/gestures#gesture-disambiguation
-  ///
-  /// By default, the drag start behavior is [DragStartBehavior.start].
-  ///
-  /// ## Example:
-  ///
-  /// A finger presses down on the screen with offset (500.0, 500.0),
-  /// and then moves to position (510.0, 500.0) before winning the arena.
-  /// With [dragStartBehavior] set to [DragStartBehavior.down], the [onStart]
-  /// callback will be called at the time corresponding to the touch's position
-  /// at (500.0, 500.0). If it is instead set to [DragStartBehavior.start],
-  /// [onStart] will be called at the time corresponding to the touch's position
-  /// at (510.0, 500.0).
-  DragStartBehavior dragStartBehavior;
+  DragGestureRecognizer({ Object debugOwner }) : super(debugOwner: debugOwner);
 
   /// A pointer has contacted the screen and might begin to move.
   ///
@@ -91,11 +60,6 @@ abstract class DragGestureRecognizer extends OneSequenceGestureRecognizer {
   ///
   /// The position of the pointer is provided in the callback's `details`
   /// argument, which is a [DragStartDetails] object.
-  ///
-  /// Depending on the value of [dragStartBehavior], this function will be
-  /// called on the initial touch down, if set to [DragStartBehavior.down] or
-  /// when the drag gesture is first detected, if set to
-  /// [DragStartBehavior.start].
   GestureDragStartCallback onStart;
 
   /// A pointer that is in contact with the screen and moving has moved again.
@@ -199,16 +163,6 @@ abstract class DragGestureRecognizer extends OneSequenceGestureRecognizer {
       _state = _DragState.accepted;
       final Offset delta = _pendingDragOffset;
       final Duration timestamp = _lastPendingEventTimestamp;
-      Offset updateDelta;
-      switch (dragStartBehavior) {
-        case DragStartBehavior.start:
-          _initialPosition = _initialPosition + delta;
-          updateDelta = Offset.zero;
-          break;
-        case DragStartBehavior.down:
-          updateDelta = _getDeltaForDetails(delta);
-          break;
-      }
       _pendingDragOffset = Offset.zero;
       _lastPendingEventTimestamp = null;
       if (onStart != null) {
@@ -217,12 +171,13 @@ abstract class DragGestureRecognizer extends OneSequenceGestureRecognizer {
           globalPosition: _initialPosition,
         )));
       }
-      if (updateDelta != Offset.zero && onUpdate != null) {
+      if (delta != Offset.zero && onUpdate != null) {
+        final Offset deltaForDetails = _getDeltaForDetails(delta);
         invokeCallback<void>('onUpdate', () => onUpdate(DragUpdateDetails(
           sourceTimeStamp: timestamp,
-          delta: updateDelta,
-          primaryDelta: _getPrimaryValueFromOffset(updateDelta),
-          globalPosition: _initialPosition + updateDelta, // Only adds delta for down behaviour
+          delta: deltaForDetails,
+          primaryDelta: _getPrimaryValueFromOffset(delta),
+          globalPosition: _initialPosition + deltaForDetails,
         )));
       }
     }
@@ -277,11 +232,6 @@ abstract class DragGestureRecognizer extends OneSequenceGestureRecognizer {
     _velocityTrackers.clear();
     super.dispose();
   }
-  @override
-  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
-    super.debugFillProperties(properties);
-    properties.add(EnumProperty<DragStartBehavior>('Start Behavior', dragStartBehavior));
-  }
 }
 
 /// Recognizes movement in the vertical direction.
@@ -330,8 +280,7 @@ class VerticalDragGestureRecognizer extends DragGestureRecognizer {
 ///    track each touch point independently.
 class HorizontalDragGestureRecognizer extends DragGestureRecognizer {
   /// Create a gesture recognizer for interactions in the horizontal axis.
-  HorizontalDragGestureRecognizer({ Object debugOwner }) :
-        super(debugOwner: debugOwner);
+  HorizontalDragGestureRecognizer({ Object debugOwner }) : super(debugOwner: debugOwner);
 
   @override
   bool _isFlingGesture(VelocityEstimate estimate) {

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

@@ -24,24 +24,6 @@ export 'pointer_router.dart' show PointerRouter;
 /// anonymous functions that return objects of particular types.
 typedef RecognizerCallback<T> = T Function();
 
-/// Configuration of offset passed to [DragStartDetails].
-///
-/// The settings determines when a drag formally starts when the user
-/// initiates a drag.
-///
-/// See also:
-///
-///   * [DragGestureRecognizer.dragStartBehavior], which gives an example for the different behaviors.
-enum DragStartBehavior {
-  /// Set the initial offset, at the position where the first down even was
-  /// detected.
-  down,
-
-  /// Set the initial position at the position where the drag start event was
-  /// detected.
-  start,
-}
-
 /// The base class that all gesture recognizers inherit from.
 ///
 /// Provides a basic API that can be used by classes that work with