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)
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。
我们可以用两种方法来解决上述问题
1. 使用灵活的部件，
Flexible小部件可以在Row、Column和Flex中使用。扩展以填充主轴中的可用空间的灵活性(例如，水平扩展[Row]或垂直扩展[Column])
但是，请记住，与Expanded不同，The Flexible小部件不需要子部件填充可用空间。所以，最好使用Flexible。
Column(
children: <Widget>[
Flexible(
child: ListView(...),
),
],
)
2. 使用shrinkWrap: true
使用shrinkWrap为true，我们告诉Listview渲染它的List到可用空间，而不是在剩余屏幕以下。
Column(
children: <Widget>[
ListView(
shrinkWrap: true,
),
],
)
此外，物理属性可以用来允许/禁止滚动Listview
停止滚动
ListView(
shrinkWrap: true,
physics: NeverScrollableScrollPhysics(),
),
允许滚动
ListView(
shrinkWrap: true,
physics: ScrollPhysics(),
),
如果你在2021年仍然面临这个问题…这里是最好的和简单的解决方案
ListView.builder(
scrollDirection: Axis.vertical,
shrinkWrap: true,
// itemExtent: 400, use this if you give hight of your items
physics: ScrollPhysics(),)
有很多解决办法。但是他们有问题…就像我们使用ListView并使用它的属性shrinkWrap .然后你会注意到滚动在ListView上不起作用所以你必须使用物理:ScrollPhysics()
