这是我的代码:
@override
Widget build(BuildContext context) {
return new Material(
color: Colors.deepPurpleAccent,
child: new Column(
mainAxisAlignment: MainAxisAlignment.center,
children:<Widget>[new GridView.count(crossAxisCount: _column,children: new List.generate(_row*_column, (index) {
return new Center(
child: new CellWidget()
);
}),)]
)
);
}
例外情况如下:
I/flutter ( 9925): ══╡ EXCEPTION CAUGHT BY RENDERING LIBRARY ╞═════════════════════════════════════════════════════════
I/flutter ( 9925): The following assertion was thrown during performResize():
I/flutter ( 9925): Vertical viewport was given unbounded height.
I/flutter ( 9925): Viewports expand in the scrolling direction to fill their container.In this case, a vertical
I/flutter ( 9925): viewport was given an unlimited amount of vertical space in which to expand. This situation
I/flutter ( 9925): typically happens when a scrollable widget is nested inside another scrollable widget.
I/flutter ( 9925): If this widget is always nested in a scrollable widget there is no need to use a viewport because
I/flutter ( 9925): there will always be enough vertical space for the children. In this case, consider using a Column
I/flutter ( 9925): instead. Otherwise, consider using the "shrinkWrap" property (or a ShrinkWrappingViewport) to size
I/flutter ( 9925): the height of the viewport to the sum of the heights of its children.
I/flutter ( 9925):
I/flutter ( 9925): When the exception was thrown, this was the stack:
I/flutter ( 9925): #0 RenderViewport.performResize.<anonymous closure> (package:flutter/src/rendering/viewport.dart:827:15)
I/flutter ( 9925): #1 RenderViewport.performResize (package:flutter/src/rendering/viewport.dart:880:6)
I/flutter ( 9925): #2 RenderObject.layout (package:flutter/src/rendering/object.dart:1555:9)
Container(
height: 100,
child: ListView.builder(
scrollDirection: Axis.vertical,
physics: BouncingScrollPhysics(),
shrinkWrap: true,
itemCount: 5,
itemBuilder: (context, index) {
return Text("Hello World $index");
},
),
);
这通常发生在你试图在一个列中使用一个ListView/GridView时，有很多方法来解决它，我在这里列出了几个。
将ListView包装为Expanded
列(
孩子们:<部件> (
Expanded(// wrap in Expanded .
孩子:列表视图(…),
)，
),
）
在sizebox中包装ListView并给出一个有界的高度
列(
孩子们:<部件> (
SizedBox (
高度:400，//固定高度
孩子:列表视图(…),
)，
),
）
在ListView中使用shrinkWrap: true。
列(
孩子们:<部件> (
列表视图(
shrinkWrap: true， //使用这个
)，
),
）
所以，每个人都上传了答案，但没有人愿意解释原因:
我将复制关于shrinkWrap的文档:
Whether the extent of the scroll view in the [scrollDirection] should be
determined by the contents being viewed.
If the scroll view does not shrink wrap, then the scroll view will expand
to the maximum allowed size in the [scrollDirection]. If the scroll view
has unbounded constraints in the [scrollDirection], then [shrinkWrap] must
be true.
Shrink wrapping the content of the scroll view is significantly more
expensive than expanding to the maximum allowed size because the content
can expand and contract during scrolling, which means the size of the
scroll view needs to be recomputed whenever the scroll position changes.
Defaults to false.
所以，从文档的词汇表来看，这里发生的是我们的ListView处于一个无限约束的情况(在我们滚动的方向上)，因此ListView会抱怨:
．.． 垂直视口被赋予无限的垂直空间
它需要扩展。
通过简单地将shrinkWrap设置为true，将确保它包装由内容定义的大小。示例代码说明:
// ...
ListView(
// Says to the `ListView` that it must wrap its
// height (if it's vertical) and width (if it's horizontal).
shrinkWrap: true,
),
// ...
这就是你的代码，尽管如此，@Rémi建议是最好的，使用Align而不是Column。
我做了一个自定义函数来解决你的问题。
你可以直接在你的代码库中使用这个函数:
Widget horizontalListView(height, width, color, child, margin) {
return Column(
children: [
SizedBox(
height: 200,
child: ListView.builder(
itemCount: 10,
shrinkWrap: true,
scrollDirection: Axis.horizontal,
itemBuilder: (context,index) {
return Container(
height: height,
width: width,
margin: EdgeInsets.all(margin),
color: color,
child: child
);
}
),
),
],
);
})
附注:对不起，代码对齐不好。
