崩溃ListView.builder

Question

我正在尝试在Flutter应用中设置搜索页面。此小组件显示搜索字段，监视用户正在键入的内容，并在搜索字段中的每个更改时更新建议的匹配列表。相关的片段在这里：

List<Text> suggestList = [new Text('')];

@override
Widget build(BuildContext context) {
  return Column(
    children: <Widget>[
      new Form(
        child: new TextFormField(
          // _controller listens for changes and updates suggestList
          controller: _controller, 
          autocorrect: false,
          decoration: InputDecoration(labelText: 'Search here'),
          onSaved: (str) => print(str),
        ),
      ),
      new ListView.builder(
        itemBuilder: (context, index) => suggestList[index],
        itemCount: suggestList.length,
      )
    ],
  );
}

此小部件崩溃时出现页面长的错误消息，但包含此文本表明我的错误是布局问题。我是Flutter和Dart的新手，无法将这些建议真正地应用于我的问题。

══╡ EXCEPTION CAUGHT BY RENDERING LIBRARY ╞═════════════════════════════════════════════════════════
The following assertion was thrown during performResize():
Vertical viewport was given unbounded height.
Viewports expand in the scrolling direction to fill their container.
In this case, a vertical
viewport was given an unlimited amount of vertical space in which to expand. 
This situation
typically happens when a scrollable widget is nested inside another 
scrollable widget.
If this widget is always nested in a scrollable widget there is no 
need to use a viewport because
there will always be enough vertical space for the children. 
In this case, consider using a Column
instead. Otherwise, consider using the "shrinkWrap" property 
(or a ShrinkWrappingViewport) to size
the height of the viewport to the sum of the heights of its children.

在下面的代码片段中，我尝试通过呈现一系列Text小部件来模拟我想要的效果：

@override
Widget build(BuildContext context) {
  return Column(
    children: <Widget>[
      new Form(
        child: new TextFormField(
          controller: _controller,
          autocorrect: false,
          decoration: InputDecoration(labelText: 'Search here'),
          onSaved: (str) => print(str),
        ),
      ),
      // Present the two first items manually as Text widgets
      suggestList[0],
      suggestList.length > 1 ? suggestList[1] : new Text('...'),
    ],
  );
}

这完美无缺，但看起来很丑陋，显然是我在最终应用中不想要的黑客。此外，我已经确认我的逻辑工作正常 - 我已经检查过suggestList总是填充了至少一个适合显示的Text小部件。关于如何修复ListView方法的任何想法？

Answer 1

一种方法是像这样构建Column子项

  @override
  Widget build(BuildContext context) {
    List<Widget> columnChildren = [
      new Form(
        child: new TextFormField(
          // _controller listens for changes and updates suggestList
          //controller: _controller,
          autocorrect: false,
          decoration: InputDecoration(labelText: 'Search here'),
          onSaved: (str) => print(str),
        ),
      )
    ];
    columnChildren.addAll(suggestList);

    return new Scaffold(
      appBar: new AppBar(
        title: new Text(widget.title),
      ),
      body: new Column(
        children: columnChildren,
      ),
    );
  }

或更好仍然只是将suggestList保持为List

  List<String> suggestList = [
    'hello',
    'world',
  ];

  @override
  Widget build(BuildContext context) {
    List<Widget> columnChildren = [
      new Form(
        child: new TextFormField(
          // _controller listens for changes and updates suggestList
          //controller: _controller,
          autocorrect: false,
          decoration: InputDecoration(labelText: 'Search here'),
          onSaved: (str) => print(str),
        ),
      )
    ];
    columnChildren.addAll(suggestList.map((s) => new Text(s)).toList());

或者，将ListView包装在Expanded

中

  body: new Column(
    children: <Widget>[
      new Form(
        child: new TextFormField(
          // _controller listens for changes and updates suggestList
          //controller: _controller,
          autocorrect: false,
          decoration: InputDecoration(labelText: 'Search here'),
          onSaved: (str) => print(str),
        ),
      ),
      new Expanded(
        child: new ListView.builder(
          itemBuilder: (context, i) => new Text(wordList[i]),
          itemCount: wordList.length,
        ),
      ),
    ],
  ),

这允许在固定表单下方的无限滚动列表。