flutter - Flutter ListView 在列内崩溃
问题描述
我需要一些帮助来弄清楚如何呈现 ListView。
我一直在关注 Flutter 教程,但我不得不停下来,因为我无法解决这个问题。
据我所知,ListView 试图占用无限量的空间,这显然会使应用程序崩溃。
我也开始明白,您不能将 ListView 作为 Column/Row 的直接子项(我在下面解释了我试图做的事情) https://flutter.io/docs/development/ui/布局/框约束#flex
这是代码:
@override
Widget build(BuildContext context) {
return Column(
children: <Widget>[
Container(
margin: EdgeInsets.all(10),
child: ProductControl(_addProduct),
),
ListView.builder(
itemCount: _products.length,
itemBuilder: (BuildContext context, int index) => Card(
child: Column(
children: <Widget>[
Image.asset('assets/food.jpg'),
Text(_products[index])
],
),
),
)
],
);
}
这就是堆栈跟踪开头所说的内容:
flutter: ══╡ EXCEPTION CAUGHT BY RENDERING LIBRARY ╞═════════════════════════════════════════════════════════
flutter: The following assertion was thrown during performResize():
flutter: Vertical viewport was given unbounded height.
flutter: Viewports expand in the scrolling direction to fill their
container.In this case, a vertical
flutter: viewport was given an unlimited amount of vertical space in
which to expand. This situation
flutter: typically happens when a scrollable widget is nested inside
another scrollable widget.
flutter: If this widget is always nested in a scrollable widget there
is no need to use a viewport because
flutter: there will always be enough vertical space for the children.
In this case, consider using a Column
flutter: instead. Otherwise, consider using the "shrinkWrap" property
(or a ShrinkWrappingViewport) to size
flutter: the height of the viewport to the sum of the heights of its children.
这是从堆栈跟踪的底部获取的:
flutter: The following RenderObject was being processed when the
exception was fired:
flutter: RenderViewport#cab62 NEEDS-LAYOUT NEEDS-PAINT
flutter: creator: Viewport ← _ScrollableScope ← IgnorePointer-
[GlobalKey#b71f9] ← Semantics ← Listener ←
flutter: _GestureSemantics ← RawGestureDetector-
[LabeledGlobalKey<RawGestureDetectorState>#d0420] ←
flutter: _ScrollSemantics-[GlobalKey#02b55] ← Scrollable ←
PrimaryScrollController ← ListView ← Column ← ⋯
flutter: parentData: <none> (can use size)
flutter: constraints: BoxConstraints(0.0<=w<=375.0, 0.0<=h<=Infinity)
flutter: size: MISSING
flutter: axisDirection: down
flutter: crossAxisDirection: right
flutter: offset: ScrollPositionWithSingleContext#892dc(offset: 0.0,
range: null..null, viewport: null,
flutter: ScrollableState, AlwaysScrollableScrollPhysics ->
BouncingScrollPhysics, IdleScrollActivity#9455f,
flutter: ScrollDirection.idle)
flutter: anchor: 0.0
flutter: This RenderObject had the following descendants (showing up to
depth 5):
flutter: RenderSliverPadding#c8ab3 NEEDS-LAYOUT NEEDS-PAINT
flutter: RenderSliverList#66f1b NEEDS-LAYOUT NEEDS-PAINT
我试图将 ListView.builder 包装在 Expanded 小部件中,但这对我不起作用。(这是教程中正在做的事情)
我试图将 Column 包装在 IntrinsicHeight 小部件中,但没有成功。
我设法解决此问题的唯一方法是将 ListView.builder 包装在具有设置高度属性的 Container 小部件中。但是在我看来,必须使用具有设定高度的 Container 并不合适。
如果需要,我可以尝试发布完整的代码以重新创建它。
解决方案
尝试使用“扩展”而不是 Container 或其他布局:
Column(
children: <Widget>[
Expanded(
//color: Colors.white,
child:
ListView.builder(
itemCount: list.length,
itemBuilder: (BuildContext context, int index) {
return ListTile(
contentPadding: EdgeInsets.all(10.0),
title: new Text('title'),
subtitle: new Text('sub title'),
onTap: () => clicked(list[index]['url']),
onLongPress: () => downloadAndStoreFile(list[index]['url'],
list[index]['name'], list[index]['title']),
);
}),
)
],
),
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