Flutter tips: various fancy nesting of listview and pageview

This time Flutter The trick is ListView and PageView Fancy nesting , Different Scrollable I believe you will not be unfamiliar with the nested conflict problem of , Passed today ListView and PageView The three nesting modes of take you to gain some different tips .

Normal nesting

The most common nesting should be horizontal PageView Plus longitudinal ListView The combination of , In general, there will be no problem with this combination , Unless you insist on sliding sideways .

Recently, I happened to meet several people asking at the same time ：“ Oblique slip ListView Easy to switch to PageView slide ” The problem of , as follows GIF Shown , When the user is sliding ListView when , After the sliding angle belt is tilted , What may cause sliding is PageView instead of ListView .

Although I don't think this is a problem from my personal experience , But if the product insists on your modification , Do you want to rewrite it yourself PageView Are your gestures responsive ？

Let's look at it briefly , Whether it's PageView still ListView Their sliding effect comes from Scrollable , and Scrollable Internal response to different directions , It's through RawGestureDetector complete ：

• VerticalDragGestureRecognizer Handle vertical gestures
• HorizontalDragGestureRecognizer Handle horizontal gestures

So simply look at the judgment logic of their response , You can see a very interesting method computeHitSlop ： according to pointer The type of determines, of course, the smallest pixel needed to hit , Touch the default is kTouchSlop (18.0).

Do you have a flash of inspiration when you see this ： If we put PageView Of touchSlop Revised , Is it possible to adjust the sensitivity of its response ？ It happens to be computeHitSlop In the method , It can go through DeviceGestureSettings To configure the , and DeviceGestureSettings From MediaQuery , So the following code shows ：

body: MediaQuery(  /// Raise height  touchSlop  To  50 , such  pageview  Sliding may have a little effect ,  /// But the problem of oblique sliding trigger is probably handled   data: MediaQuery.of(context).copyWith(      gestureSettings: DeviceGestureSettings(    touchSlop: 50,  )),  child: PageView(    scrollDirection: Axis.horizontal,    pageSnapping: true,    children: [      HandlerListView(),      HandlerListView(),    ],  ),),

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Tip 1 ： By nesting a MediaQuery , Then adjust gestureSettings Of touchSlop To modify PageView The lightness of , And don't forget , You need to put ListView Of touchSlop Switching will default Of kTouchSlop ：

class HandlerListView extends StatefulWidget {  @override  _MyListViewState createState() => _MyListViewState();}class _MyListViewState extends State<HandlerListView> {  @override  Widget build(BuildContext context) {    return MediaQuery(      /// here  touchSlop   You need to return to the default       data: MediaQuery.of(context).copyWith(          gestureSettings: DeviceGestureSettings(        touchSlop: kTouchSlop,      )),      child: ListView.separated(        itemCount: 15,        itemBuilder: (context, index) {          return ListTile(            title: Text('Item $index'),          );        },        separatorBuilder: (context, index) {          return const Divider(            thickness: 3,          );        },      ),    );  }}

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Finally, let's see the effect , as follows GIF Shown , Now even if you slide sideways , It also triggers PageView Horizontal sliding of , Triggered only when moving laterally PageView The gesture , Of course , If there is any problem with this rough writing , It's probably reduced PageView Sensitivity of response .

In the same direction PageView nesting ListView

After introducing the general use , Then something different , Switch vertically PageView Nested vertically scrolling ListView , Is your first feeling unreliable , Why is there such a scene ？

For products , They won't think about how you achieve it , They just slap their heads and say Taobao can , Why can't you , So if it's you , What would you do ？

And about this demand , The result of the current discussion in the community is ： hold PageView and ListView Sliding of is disabled , And then through RawGestureDetector Manage yourself .

If you are not interested in implementing logical analysis , You can see directly at the end of this section Source link .

Don't panic when you see your own management , Although we should realize it by ourselves PageView and ListView Gesture distribution , But there is no need to rewrite PageView and ListView , We can reuse their Darg Response logic , As shown in the following code ：

• adopt NeverScrollableScrollPhysics It's forbidden PageView and ListView The rolling effect of
• Through the top RawGestureDetector Of VerticalDragGestureRecognizer Manage gesture events by yourself
• To configure PageController and ScrollController Used to get status

body: RawGestureDetector(  gestures: <Type, GestureRecognizerFactory>{    VerticalDragGestureRecognizer: GestureRecognizerFactoryWithHandlers<            VerticalDragGestureRecognizer>(        () => VerticalDragGestureRecognizer(),        (VerticalDragGestureRecognizer instance) {      instance        ..onStart = _handleDragStart        ..onUpdate = _handleDragUpdate        ..onEnd = _handleDragEnd        ..onCancel = _handleDragCancel;    })  },  behavior: HitTestBehavior.opaque,  child: PageView(    controller: _pageController,    scrollDirection: Axis.vertical,    /// Mask the default sliding response     physics: const NeverScrollableScrollPhysics(),    children: [      ListView.builder(        controller: _listScrollController,        /// Mask the default sliding response         physics: const NeverScrollableScrollPhysics(),        itemBuilder: (context, index) {          return ListTile(title: Text('List Item $index'));        },        itemCount: 30,      ),      Container(        color: Colors.green,        child: Center(          child: Text(            'Page View',            style: TextStyle(fontSize: 50),          ),        ),      )    ],  ),),

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And then let's see _handleDragStart Realization , As shown in the following code , Making gestures details when , We mainly judge ：

• adopt ScrollController Judge ListView Whether or not visible
• Judge whether the touch position is ListIView Within the scope of
• Judge which one to pass according to the status Controller To produce Drag object , Used to respond to subsequent sliding events

​  void _handleDragStart(DragStartDetails details) {    /// First judge  Listview  Whether it is visible or can be called     /// Generally invisible  hasClients false , because  PageView  either  keepAlive    if (_listScrollController?.hasClients == true &&        _listScrollController?.position.context.storageContext != null) {      /// obtain  ListView  Of   renderBox      final RenderBox? renderBox = _listScrollController          ?.position.context.storageContext          .findRenderObject() as RenderBox;​      /// Judge whether the touch position is  ListView  Inside       /// Generally, it is not within the scope because  ListView  It has slid up , The coordinate position is inconsistent with the touch position       if (renderBox?.paintBounds              .shift(renderBox.localToGlobal(Offset.zero))              .contains(details.globalPosition) ==          true) {        _activeScrollController = _listScrollController;        _drag = _activeScrollController?.position.drag(details, _disposeDrag);        return;      }    }​    /// At this time, it can be regarded as  PageView  Need to slide     _activeScrollController = _pageController;    _drag = _pageController?.position.drag(details, _disposeDrag);  }

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We are mainly at the beginning of touch , When judging the object that needs response ListView still PageView , And then through _activeScrollController Save the response object of course , And through Controller Generate Drag object .

In short ： When the sliding event occurs , By default, a Drag Used to handle subsequent sliding events ,Drag The original event will be processed and then given ScrollPosition To trigger the subsequent sliding effect .

And then _handleDragUpdate In the method , It mainly determines whether the response needs to be switched to PageView:

• If you don't need it, continue to use what you got before _drag?.update(details) Respond to ListView rolling
• If necessary, pass _pageController Switch to new _drag Object is used to respond to

void _handleDragUpdate(DragUpdateDetails details) {  if (_activeScrollController == _listScrollController &&​      /// Move your fingers up , That is, it is about to show the bottom  PageView      details.primaryDelta! < 0 &&​      /// At the bottom , Switch to  PageView      _activeScrollController?.position.pixels ==          _activeScrollController?.position.maxScrollExtent) {    /// Switch the corresponding controller     _activeScrollController = _pageController;    _drag?.cancel();​    /// Reference resources   Scrollable  in     /// Because it is switching controller , That is to update  Drag    /// Drag and drop the process to switch to  PageView  in , So we need to   DragStartDetails    /// So we need to  DragUpdateDetails  become  DragStartDetails    /// Extract  PageView  Inside  Drag  The corresponding  details    _drag = _pageController?.position.drag(        DragStartDetails(            globalPosition: details.globalPosition,            localPosition: details.localPosition),        _disposeDrag);  }  _drag?.update(details);}

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Here is a little knowledge ： As shown in the above code , We can simply go through details.primaryDelta Judge whether the sliding direction and moving is the spindle

Finally, as follows GIF Shown , You can see PageView nesting ListView Sliding in the same direction can work normally , But there are still two small problems , As can be seen from the illustration ：

• After switching ListView The location of has not been saved
• The product requires removal ListView Edge overflow effect

So we need to deal with ListView Make one KeepAlive , Then use a simple method to remove Android Edge sliding Material effect ：

• adopt with AutomaticKeepAliveClientMixin Give Way ListView Keep the sliding position after switching
• adopt ScrollConfiguration.of(context).copyWith(overscroll: false) Rapid removal Scrollable The edge of Material effect

child: PageView(  controller: _pageController,  scrollDirection: Axis.vertical,  /// Get rid of  Android  On the default edge drag effect   scrollBehavior:      ScrollConfiguration.of(context).copyWith(overscroll: false),​​/// Yes  PageView  Inside  ListView  do  KeepAlive  Remember the location class KeepAliveListView extends StatefulWidget {  final ScrollController? listScrollController;  final int itemCount;​  KeepAliveListView({    required this.listScrollController,    required this.itemCount,  });​  @override  KeepAliveListViewState createState() => KeepAliveListViewState();}​class KeepAliveListViewState extends State<KeepAliveListView>    with AutomaticKeepAliveClientMixin {  @override  Widget build(BuildContext context) {    super.build(context);    return ListView.builder(      controller: widget.listScrollController,​      /// Mask the default sliding response       physics: const NeverScrollableScrollPhysics(),      itemBuilder: (context, index) {        return ListTile(title: Text('List Item $index'));      },      itemCount: widget.itemCount,    );  }​  @override  bool get wantKeepAlive => true;}

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So here we have another trick to unlock ： adopt ScrollConfiguration.of(context).copyWith(overscroll: false) Rapid removal Android Sliding to the edge Material 2 effect , Why do you say Material2, because Material3 Change up , concrete ： Flutter 3 Under the ThemeExtensions and Material3 .

The source code of this section can be seen ： https://github.com/CarGuo/gsy_flutter_demo/blob/7838971cefbf19bb53a71041cd100c4c15eb6443/lib/widget/vp_list_demo_page.dart#L75

In the same direction ListView nesting PageView

Is there anything more unconventional ？ The answer is yes , After all, the small head of the product , How can I not think of Sliding vertically ListView Nested vertically switched PageView This demand .

With the front idea , In fact, the realization of this logic is similar ： hold PageView and ListView Sliding of is disabled , And then through RawGestureDetector Manage yourself , The difference is the difference in gesture distribution .

RawGestureDetector(          gestures: <Type, GestureRecognizerFactory>{            VerticalDragGestureRecognizer: GestureRecognizerFactoryWithHandlers<                    VerticalDragGestureRecognizer>(                () => VerticalDragGestureRecognizer(),                (VerticalDragGestureRecognizer instance) {              instance                ..onStart = _handleDragStart                ..onUpdate = _handleDragUpdate                ..onEnd = _handleDragEnd                ..onCancel = _handleDragCancel;            })          },          behavior: HitTestBehavior.opaque,          child: ListView.builder(                /// Mask the default sliding response                 physics: NeverScrollableScrollPhysics(),                controller: _listScrollController,                itemCount: 5,                itemBuilder: (context, index) {                  if (index == 0) {                    return Container(                      height: 300,                      child: KeepAlivePageView(                        pageController: _pageController,                        itemCount: itemCount,                      ),                    );                  }                  return Container(                      height: 300,                      color: Colors.greenAccent,                      child: Center(                        child: Text(                          "Item $index",                          style: TextStyle(fontSize: 40, color: Colors.blue),                        ),                      ));                }),        )

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It's also in _handleDragStart In the method , First of all, we need to judge ：

• ListView If it has slipped , Will not respond to the top PageView Events
• If at this time ListView Not sliding at the top , Judge whether the gesture position is PageView in , If it's a response PageView Events

  void _handleDragStart(DragStartDetails details) {    /// As long as it's not the top , No response  PageView  The slide of     /// So this judgment only supports vertical  PageView  stay   ListView  At the top of the     if (_listScrollController.offset > 0) {      _activeScrollController = _listScrollController;      _drag = _listScrollController.position.drag(details, _disposeDrag);      return;    }​    /// At this time   ListView  At the top of the     if (_pageController.hasClients) {      /// obtain  PageView      final RenderBox renderBox =          _pageController.position.context.storageContext.findRenderObject()              as RenderBox;​      /// Judge whether the touch range is  PageView      final isDragPageView = renderBox.paintBounds          .shift(renderBox.localToGlobal(Offset.zero))          .contains(details.globalPosition);​      /// If in  PageView  Switch to  PageView      if (isDragPageView) {        _activeScrollController = _pageController;        _drag = _activeScrollController.position.drag(details, _disposeDrag);        return;      }    }​    /// be not in  PageView  I will continue to respond  ListView    _activeScrollController = _listScrollController;    _drag = _listScrollController.position.drag(details, _disposeDrag);  }

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And then _handleDragUpdate In the method , Determine if the PageView Has slid to the last page , Also switch the sliding event to ListView

void _handleDragUpdate(DragUpdateDetails details) {  var scrollDirection = _activeScrollController.position.userScrollDirection;​  /// Judge if the response at this time is still  _pageController, Is it the last page   if (_activeScrollController == _pageController &&      scrollDirection == ScrollDirection.reverse &&​      /// Is it the last page , Switch back to... On the last page  pageController      (_pageController.page != null &&          _pageController.page! >= (itemCount - 1))) {    /// Switch back to the  ListView    _activeScrollController = _listScrollController;    _drag?.cancel();    _drag = _listScrollController.position.drag(        DragStartDetails(            globalPosition: details.globalPosition,            localPosition: details.localPosition),        _disposeDrag);  }  _drag?.update(details);}

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Of course , As well as KeepAlive And remove the list Material Edge effect , The results are as follows GIF Shown .

The source code of this section can be seen ：https://github.com/CarGuo/gsy_flutter_demo/blob/7838971cefbf19bb53a71041cd100c4c15eb6443/lib/widget/vp_list_demo_page.dart#L262

Finally, add a little trick ： If you need Flutter Print the process of gesture competition , You can configure the debugPrintGestureArenaDiagnostics = true; To make the Flutter The processing process of outputting gesture competition .

import 'package:flutter/gestures.dart';void main() {  debugPrintGestureArenaDiagnostics = true;  runApp(MyApp());}

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Last

So to conclude , This chapter introduces how to pass Darg Solve various gesture conflicts caused by nesting , I believe you also know how to use Controller and Darg To quickly customize some sliding requirements , for example ListView linkage ListView Differential sliding effect ：

///listView  linkage  listViewclass ListViewLinkListView extends StatefulWidget {  @override  _ListViewLinkListViewState createState() => _ListViewLinkListViewState();}​class _ListViewLinkListViewState extends State<ListViewLinkListView> {  ScrollController _primaryScrollController = ScrollController();  ScrollController _subScrollController = ScrollController();​  Drag? _primaryDrag;  Drag? _subDrag;​  @override  void initState() {    super.initState();  }​  @override  void dispose() {    _primaryScrollController.dispose();    _subScrollController.dispose();    super.dispose();  }​  void _handleDragStart(DragStartDetails details) {    _primaryDrag =        _primaryScrollController.position.drag(details, _disposePrimaryDrag);    _subDrag = _subScrollController.position.drag(details, _disposeSubDrag);  }​  void _handleDragUpdate(DragUpdateDetails details) {    _primaryDrag?.update(details);​    /// Divide 10 Achieve the difference effect     _subDrag?.update(DragUpdateDetails(        sourceTimeStamp: details.sourceTimeStamp,        delta: details.delta / 30,        primaryDelta: (details.primaryDelta ?? 0) / 30,        globalPosition: details.globalPosition,        localPosition: details.localPosition));  }​  void _handleDragEnd(DragEndDetails details) {    _primaryDrag?.end(details);    _subDrag?.end(details);  }​  void _handleDragCancel() {    _primaryDrag?.cancel();    _subDrag?.cancel();  }​  void _disposePrimaryDrag() {    _primaryDrag = null;  }​  void _disposeSubDrag() {    _subDrag = null;  }​  @override  Widget build(BuildContext context) {    return Scaffold(        appBar: AppBar(          title: Text("ListViewLinkListView"),        ),        body: RawGestureDetector(          gestures: <Type, GestureRecognizerFactory>{            VerticalDragGestureRecognizer: GestureRecognizerFactoryWithHandlers<                    VerticalDragGestureRecognizer>(                () => VerticalDragGestureRecognizer(),                (VerticalDragGestureRecognizer instance) {              instance                ..onStart = _handleDragStart                ..onUpdate = _handleDragUpdate                ..onEnd = _handleDragEnd                ..onCancel = _handleDragCancel;            })          },          behavior: HitTestBehavior.opaque,          child: ScrollConfiguration(            /// Get rid of  Android  On the default edge drag effect             behavior:                ScrollConfiguration.of(context).copyWith(overscroll: false),            child: Row(              children: [                new Expanded(                    child: ListView.builder(​                        /// Mask the default sliding response                         physics: NeverScrollableScrollPhysics(),                        controller: _primaryScrollController,                        itemCount: 55,                        itemBuilder: (context, index) {                          return Container(                              height: 300,                              color: Colors.greenAccent,                              child: Center(                                child: Text(                                  "Item $index",                                  style: TextStyle(                                      fontSize: 40, color: Colors.blue),                                ),                              ));                        })),                new SizedBox(                  width: 5,                ),                new Expanded(                  child: ListView.builder(​                      /// Mask the default sliding response                       physics: NeverScrollableScrollPhysics(),                      controller: _subScrollController,                      itemCount: 55,                      itemBuilder: (context, index) {                        return Container(                          height: 300,                          color: Colors.deepOrange,                          child: Center(                            child: Text(                              "Item $index",                              style:                                  TextStyle(fontSize: 40, color: Colors.white),                            ),                          ),                        );                      }),                ),              ],            ),          ),        ));  }}

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