颤振:如何防止重建整个可重新排序的列表视图?

Question

目前我正在使用颤振包"可重新排序"来显示包含多个图像的可重新排序列表视图。这些图像可以通过一个按钮从列表视图中删除，一切正常。但是每次删除图像时，列表视图都会重建。我正在使用一个名为"ReorderableListviewManager"的类与ChangeNotifier一起更新图像，并Provider.of<ReorderableListviewManager>(context)以获取最新图像。现在的问题是，每次删除图像时，使用Provider.of<ReorderableListviewManager>(context)都会调用build()，因此列表视图 rebuid。我呜 可以使用 Consumer 来仅重建小部件树的一部分，但似乎没有地方可以将 Consumer 放在此列表视图children。有没有办法只重建图像而不是整个可重新排序列表视图？非常感谢！

下面是我的代码：

class NotePicturesEditScreen extends StatefulWidget {
final List<Page> notePictures;
final NotePicturesEditBloc bloc;
NotePicturesEditScreen({@required this.notePictures, @required this.bloc});
static Widget create(BuildContext context, List<Page> notePictures) {
return Provider<NotePicturesEditBloc>(
create: (context) => NotePicturesEditBloc(),
child: Consumer<NotePicturesEditBloc>(
builder: (context, bloc, _) =>
ChangeNotifierProvider<ReorderableListviewManager>(
create: (context) => ReorderableListviewManager(),
child: NotePicturesEditScreen(
bloc: bloc,
notePictures: notePictures,
),
)),
dispose: (context, bloc) => bloc.dispose(),
);
}
@override
_NotePicturesEditScreenState createState() => _NotePicturesEditScreenState();
}
class _NotePicturesEditScreenState extends State<NotePicturesEditScreen> {
PreloadPageController _pageController;
ScrollController _reorderableScrollController;
List<Page> notePicturesCopy;
int longPressIndex;
List<double> smallImagesWidth;
double scrollOffset = 0;
_reorderableScrollListener() {
scrollOffset = _reorderableScrollController.offset;
}
@override
void initState() {
Provider.of<ReorderableListviewManager>(context, listen: false)
.notePictures = widget.notePictures;
notePicturesCopy = widget.notePictures;
_reorderableScrollController = ScrollController();
_pageController = PreloadPageController();
_reorderableScrollController.addListener(_reorderableScrollListener);
Provider.of<ReorderableListviewManager>(context, listen: false)
.getSmallImagesWidth(notePicturesCopy, context)
.then((imagesWidth) {
smallImagesWidth = imagesWidth;
});
super.initState();
}
@override
void dispose() {
_pageController.dispose();
_reorderableScrollController.dispose();
super.dispose();
}
@override
Widget build(BuildContext context) {
ReorderableListviewManager reorderableManager =
Provider.of<ReorderableListviewManager>(context, listen: false);
return SafeArea(
child: Scaffold(
appBar: AppBar(
backgroundColor: Colors.white,
shape: Border(bottom: BorderSide(color: Colors.black12)),
iconTheme: IconThemeData(color: Colors.black87),
elevation: 0,
automaticallyImplyLeading: false,
titleSpacing: 0,
centerTitle: true,
title: Row(
mainAxisAlignment: MainAxisAlignment.start,
crossAxisAlignment: CrossAxisAlignment.center,
children: <Widget>[
Container(
child: IconButton(
padding: EdgeInsets.only(left: 20, right: 12),
onPressed: () => Navigator.of(context).pop(),
icon: Icon(Icons.close),
),
),
Text('編輯',
style: TextStyle(color: Colors.black87, fontSize: 18))
],
),
actions: <Widget>[
FlatButton(
onPressed: () {},
child: Text(
'下一步',
),
)
],
),
backgroundColor: Color(0xffeeeeee),
body: Column(
mainAxisAlignment: MainAxisAlignment.start,
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
Spacer(),
StreamBuilder<List<Page>>(
initialData: widget.notePictures,
stream: widget.bloc.notePicturesStream,
builder: (context, snapshot) {
notePicturesCopy = snapshot.data;
return Container(
margin: EdgeInsets.symmetric(horizontal: 20),
height: MediaQuery.of(context).size.height * 0.65,
child: PreloadPageView.builder(
preloadPagesCount: snapshot.data.length,
controller: _pageController,
itemCount: snapshot.data.length,
onPageChanged: (index) {
reorderableManager.updateCurrentIndex(index);
reorderableManager.scrollToCenter(
smallImagesWidth,
index,
scrollOffset,
_reorderableScrollController,
context);
},
itemBuilder: (context, index) {
return Container(
child: Image.memory(
File.fromUri(
snapshot.data[index].polygon.isNotEmpty
? snapshot.data[index]
.documentPreviewImageFileUri
: snapshot.data[index]
.originalPreviewImageFileUri)
.readAsBytesSync(),
gaplessPlayback: true,
alignment: Alignment.center,
),
);
}),
);
},
),
Spacer(),
Container(
height: MediaQuery.of(context).size.height * 0.1,
margin: EdgeInsets.symmetric(horizontal: 20),
child: SingleChildScrollView(
scrollDirection: Axis.horizontal,
child: ReorderableRow(
scrollController: _reorderableScrollController,
buildDraggableFeedback: (context, constraints, __) =>
Container(
width: constraints.maxWidth,
height: constraints.maxHeight,
child: Image.memory(File.fromUri(
notePicturesCopy[longPressIndex]
.polygon
.isNotEmpty
? notePicturesCopy[longPressIndex]
.documentPreviewImageFileUri
: notePicturesCopy[longPressIndex]
.originalPreviewImageFileUri)
.readAsBytesSync()),
),
onReorder: (oldIndex, newIndex) async {
List<Page> result = await widget.bloc.reorderPictures(
oldIndex,
newIndex,
reorderableManager.notePictures);
_pageController.jumpToPage(newIndex);
reorderableManager.updateNotePictures(result);
reorderableManager
.getSmallImagesWidth(result, context)
.then((imagesWidth) {
smallImagesWidth = imagesWidth;
});
},
footer: Container(
width: 32,
height: 32,
margin: EdgeInsets.only(left: 16),
child: SizedBox(
child: FloatingActionButton(
backgroundColor: Colors.white,
elevation: 1,
disabledElevation: 0,
highlightElevation: 1,
child: Icon(Icons.add, color: Colors.blueAccent),
onPressed: notePicturesCopy.length >= 20
? () {
Scaffold.of(context)
.showSnackBar(SnackBar(
content: Text('筆記上限為20頁 !'),
));
}
: () async {
List<Page> notePictures =
await widget.bloc.addPicture(
reorderableManager.notePictures);
List<double> imagesWidth =
await reorderableManager
.getSmallImagesWidth(
notePictures, context);
smallImagesWidth = imagesWidth;
reorderableManager.updateCurrentIndex(
notePictures.length - 1);
reorderableManager
.updateNotePictures(notePictures);
_pageController
.jumpToPage(notePictures.length - 1);
},
),
),
),
children: Provider.of<ReorderableListviewManager>(
context) 
.notePictures
.asMap()
.map((index, page) {
return MapEntry(
index,
Consumer<ReorderableListviewManager>(
key: ValueKey('value$index'),
builder: (context, manager, _) =>
GestureDetector(
onTapDown: (_) {
longPressIndex = index;
},
onTap: () {
reorderableManager.scrollToCenter(
smallImagesWidth,
index,
scrollOffset,
_reorderableScrollController,
context);
_pageController.jumpToPage(index);
},
child: Container(
margin: EdgeInsets.only(
left: index == 0 ? 0 : 12),
decoration: BoxDecoration(
border: Border.all(
width: 1.5,
color: index ==
manager
.getCurrentIndex
? Colors.blueAccent
: Colors.transparent)),
child: index + 1 <=
manager.notePictures.length
? Image.memory(
File.fromUri(manager
.notePictures[
index]
.polygon
.isNotEmpty
? manager
.notePictures[
index]
.documentPreviewImageFileUri
: manager
.notePictures[
index]
.originalPreviewImageFileUri)
.readAsBytesSync(),
gaplessPlayback: true,
)
: null),
),
));
})
.values
.toList()),
)),
Spacer(),
Container(
decoration: BoxDecoration(
color: Colors.white,
border: Border(top: BorderSide(color: Colors.black12))),
child: Row(
mainAxisAlignment: MainAxisAlignment.spaceEvenly,
children: <Widget>[
FlatButton(
onPressed: () async => await widget.bloc
.cropNotePicture(reorderableManager.notePictures,
_pageController.page.round())
.then((notePictures) {
reorderableManager.updateNotePictures(notePictures);
reorderableManager
.getSmallImagesWidth(notePictures, context)
.then((imagesWidth) {
smallImagesWidth = imagesWidth;
});
}),
child: Column(
children: <Widget>[
Icon(
Icons.crop,
color: Colors.blueAccent,
),
Container(
margin: EdgeInsets.only(top: 1),
child: Text(
'裁切',
style: TextStyle(color: Colors.blueAccent),
),
)
],
),
),
FlatButton(
onPressed: () {
int deleteIndex = _pageController.page.round();
widget.bloc
.deletePicture(
reorderableManager.notePictures, deleteIndex)
.then((notePictures) {
if (deleteIndex == notePictures.length) {
reorderableManager
.updateCurrentIndex(notePictures.length - 1);
}
reorderableManager.updateNotePictures(notePictures);
reorderableManager
.getSmallImagesWidth(notePictures, context)
.then((imagesWidth) {
smallImagesWidth = imagesWidth;
});
if (reorderableManager.notePictures.length == 0) {
Navigator.pop(context);
}
});
},
child: Column(
children: <Widget>[
Icon(
Icons.delete_outline,
color: Colors.blueAccent,
),
Container(
margin: EdgeInsets.only(top: 1),
child: Text(
'刪除',
style: TextStyle(color: Colors.blueAccent),
),
),
],
),
)
],
),
)
],
)),
);
}
}

Answer 1

您无法阻止在可重新排序列表视图小部件上重新生成，因为每次提供程序上有更新时都会重新生成它。您可以在此处执行的操作是跟踪所有可见 ListView 项的当前索引。当应显示来自提供程序的新数据时，可以保留以前 ListView 项的当前索引，并将新添加的项添加到列表末尾或所需的任何位置。