我有一个工作页面，它是使用 Listview.builder 的动态消息 ListView 。 itembuilder 调用创建卡片的小部件。我想要做的是将第一个列表更改为一个分隔符，它将是一个日期，然后将调用该日期之前的项目列表。正在创建所有数据调用和列表，但不断出现 hasSize is not true 错误，并且看不出大小哪里有问题，我只是使用了相同的布局。

不确定要显示什么代码以获得帮助，所以如果您有任何想法以及可能需要查看哪些代码，请告诉我。

这是在更改之前有效的开始:

var _children = <Widget>[

  new Expanded(
    child: new RefreshIndicator(
      child: new ListView.builder(
        itemBuilder: _divBuilder,
        itemCount: listcount,
      ),
      onRefresh: _onRefresh,
    ),
  ),
  new Stack(
    alignment: Alignment.centerRight,
    children: <Widget>[
      new TextField(
        decoration: const InputDecoration(
          hintText: 'Chat Reply',
          labelText: 'Chat Reply:',
        ),
        autofocus: false,
        focusNode: _focusnode,
        maxLines: 2,
        controller: _newreplycontroller,
        keyboardType: TextInputType.url,
      ),
      new IconButton(
        icon: new Icon(Icons.send),
        onPressed: _sendReply,
        alignment: Alignment.centerRight,
      )
    ],
  ),
];
return new Scaffold(
  appBar: new AppBar(
    title: mytitle,
    actions: getAppBarActions(context),
  ),
  body: new Column(
    mainAxisSize: MainAxisSize.max,
    children: _children,
  ),
);

现在我有 2 个正在使用的小部件。

    class MyChatWidget extends StatefulWidget {
  MyChatWidget({Key key, this.datediv, this.msgkey}) : super(key: key);

  final DateTime datediv;
  final String msgkey;

  @override
  _MyChatWidgetState createState() => new _MyChatWidgetState();
}

class _MyChatWidgetState extends State<MyChatWidget> {
  List messagelist;
  int messagecount = 0;
  var jsonCodec = const JsonCodec();

  _getMessages() async {
    var _url = 'http://$baseurl/csapi/messages/getbydate';
    DateChatMessage dcm = new DateChatMessage(widget.msgkey, widget.datediv.toString());
    var json = jsonCodec.encode(dcm);
    var http = createHttpClient();
    var response = await http.post(_url, headers: getAuthHeader(), body: json);

    var messages = await jsonCodec.decode(response.body);

    if (mounted) {
      setState(() {
        messagelist = messages.toList();
        messagecount = messagelist.length;
        //replysub = 'Re: ' + chatlist[0]['sub'];
      });
    }
  }

  @override
  void initState() {
    super.initState();
    //controller = new TabController(length: 4, vsync: this);
    _getMessages();
  }

  @override
  Widget build(BuildContext context) {
    var _children = <Widget>[
      new Divider(height: 5.0,color: Colors.red,),
      new Expanded(
        child: new ListView.builder(
          itemBuilder: _itemBuilder,
          itemCount: messagecount,
        ),
      ),

    ];


    return new Column(
        mainAxisSize: MainAxisSize.min,
        children: _children,
      );
  }

  Widget _itemBuilder(BuildContext context, int index) {
    ChatMessage mychat = getChat(index);
    return new ChatWidget(
      mychat: mychat,
    );
  }

  ChatMessage getChat(int index) {
    //prefs.setInt('pid', myReferralList[index]['pid']);
    return new ChatMessage(
      messagelist[index]['msgkey'],
      messagelist[index]['referralname'],
      messagelist[index]['sub'],
      messagelist[index]['oid'],
      messagelist[index]['oname'],
      messagelist[index]['pid'],
      messagelist[index]['pname'],
      messagelist[index]['sender'],
      messagelist[index]['sendname'],
      messagelist[index]['receiver'],
      messagelist[index]['receivename'],
      messagelist[index]['message'],
      messagelist[index]['submitdate'],
      messagelist[index]['pgrpid'],
      messagelist[index]['prid'],
      messagelist[index]['fcmtoken'],
    );
  }
}


class ChatWidget extends StatefulWidget {
  ChatWidget({Key key, this.mychat}) : super(key: key);

  final ChatMessage mychat;

  @override
  _ChatWidgetState createState() => new _ChatWidgetState();
}

class _ChatWidgetState extends State<ChatWidget> {
  @override
  Widget build(BuildContext context) {
    DateTime submitdate = DateTime.parse(widget.mychat.submitdate).toLocal();

    return new Card(
      child: new Container(
        width: 150.0,
        padding: new EdgeInsets.all(10.0),
        child: new Column(
          mainAxisAlignment: MainAxisAlignment.start,
          crossAxisAlignment: CrossAxisAlignment.start,
          mainAxisSize: MainAxisSize.min,
          children: <Widget>[
            new Row(
              children: <Widget>[
                new Text(
                  widget.mychat.sendname,
                  style: new TextStyle(
                      fontSize: 15.0, fontWeight: FontWeight.bold),
                ),
                new Text(' @ '),
                new Text(new DateFormat.yMd().add_Hm().format(submitdate)),
                //new Text(submitdate.toLocal().toString())
              ],
            ),

            //new Text(widget.mychat.receivename,style: new TextStyle(fontSize: 15.0, fontWeight: FontWeight.bold),),
            //new Text(new DateFormat.yMd().add_Hm().format(submitdate)),
            new Text('${widget.mychat.message}'),
          ],
        ),
      ),
    );
    /*return new ListTile(
      leading: new CircleAvatar(child: new Text(widget.mychat.oname[0])),
      title: new Text(widget.mychat.referralname),
      subtitle: new Text(new DateFormat.yMd().add_Hm().format(submitdate)),
      trailing: new Text(widget.mychat.sendname),
      onTap: _onTap,
    );*/
  }



void _onTap() {
    Route route = new MaterialPageRoute(
      settings: new RouteSettings(name: "/chats/chatconvodetil"),
      builder: (BuildContext context) =>
      new ChatConvoDetail(mychat: widget.mychat),
    );
    Navigator.of(context).push(route);
  }
}

任何指导都会很棒

完整错误堆栈

══╡ EXCEPTION CAUGHT BY RENDERING LIBRARY 

╞═════════════════════════════════════════════════════════
RenderFlex children have non-zero flex but incoming height constraints are unbounded.
When a column is in a parent that does not provide a finite height constraint, for example if it is
in a vertical scrollable, it will try to shrink-wrap its children along the vertical axis. Setting a
space in the vertical direction.
These two directives are mutually exclusive. If a parent is to shrink-wrap its child, the child
cannot simultaneously expand to fit its parent.
Consider setting mainAxisSize to MainAxisSize.min and using FlexFit.loose fits for the flexible
themselves to less than the infinite remaining space they would otherwise be forced to take, and
then will cause the RenderFlex to shrink-wrap the children rather than expanding to fit the maximum
constraints provided by the parent.
The affected RenderFlex is:
RenderFlex#d88d8 relayoutBoundary=up8 NEEDS-LAYOUT NEEDS-PAINT
The creator information is set to:
Column ← MyChatWidget ← RepaintBoundary-[<0>] ← NotificationListener<KeepAliveNotification> ←
KeepAlive ← AutomaticKeepAlive ← SliverList ← ShrinkWrappingViewport ← _ScrollableScope ←
IgnorePointer-[GlobalKey#ac8f6] ← Listener ← _GestureSemantics ← ⋯
See also: https://flutter.io/layout/
https://flutter.io/debugging/#rendering-layer
http://docs.flutter.io/flutter/rendering/debugDumpRenderTree.html
If none of the above helps enough to fix this problem, please don't hesitate to file a bug:
https://github.com/flutter/flutter/issues/new

When the exception was thrown, this was the stack:

The following RenderObject was being processed when the exception was fired:
RenderFlex#d88d8 relayoutBoundary=up8 NEEDS-LAYOUT NEEDS-PAINT
creator: Column ← MyChatWidget ← RepaintBoundary-[<0>] ←
NotificationListener<KeepAliveNotification> ← KeepAlive ← AutomaticKeepAlive ← SliverList ←
ShrinkWrappingViewport ← _ScrollableScope ← IgnorePointer-[GlobalKey#ac8f6] ← Listener ←
_GestureSemantics ← ⋯
size: MISSING
direction: vertical
mainAxisAlignment: start
mainAxisSize: min
crossAxisAlignment: center
verticalDirection: down
RenderConstrainedBox#1d682 relayoutBoundary=up9 NEEDS-PAINT
RenderPositionedBox#d9c42 relayoutBoundary=up10 NEEDS-PAINT
RenderPadding#c357c relayoutBoundary=up11 NEEDS-PAINT
RenderConstrainedBox#3ad51 relayoutBoundary=up12 NEEDS-PAINT
RenderDecoratedBox#e68e0 relayoutBoundary=up13 NEEDS-PAINT
RenderSemanticsGestureHandler#83b48 NEEDS-LAYOUT NEEDS-PAINT
RenderPointerListener#9b129 NEEDS-LAYOUT NEEDS-PAINT
RenderIgnorePointer#aa9c2 NEEDS-LAYOUT NEEDS-PAINT
RenderShrinkWrappingViewport#f658c NEEDS-LAYOUT NEEDS-PAINT
RenderSliverList#7b88e NEEDS-LAYOUT NEEDS-PAINT
════════════════════════════════════════════════════════════════════════════════════════════════════
Another exception was thrown: 'package:flutter/src/rendering/box.dart': Failed assertion: line 1433 pos 12: 'hasSize': is not true.
Another exception was thrown: 'package:flutter/src/rendering/sliver_multi_box_adaptor.dart': Failed assertion: line 455 pos 12: 'child.hasSize': is not true.

最佳答案

'hasSize': is not true 通常与具有不受约束大小的 Column 或 Row 有关，因此 Flutter 无法识别它应该在多大空间内呈现这两个小部件。但是，在您的情况下，我相信这是由您的 ListView.builder 引起的，请尝试在 中设置 shr​​inkWrap 属性>ListView.builder 设置为 true 并查看它是否解决了您的问题，否则它是由 Column 或 Row 引起的。但我想设置 shr​​inkWrap:true 应该可以解决它，所以先试试吧。

在深入了解有关错误的详细信息后，似乎将 Expanded 更改为 Flexible 已解决问题。

关于Flutter Listview of items as divider 与 Listview of items Size 问题，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/47244779/