展开原因“ BoxConstraints强制无限宽度和无限高度”。在某些情况下

Question

摘要

当我的自定义窗口小部件位于扩展窗口小部件（扩展>行> CustomWidget）内部的行中时，它的效果很好。但是，如果我随后将自定义窗口小部件包装在行内的一列内（展开>行>列> CustomWidget），则会引发一个断言：“ BoxConstraints强制无限宽度和无限高度。”

我了解断言的要旨，但我不明白为什么在行和自定义小部件之间添加列会导致问题出现，而以前根本就不存在。如果没有该列，则必须将约束从父项传递到树状结构的子项。将专栏放在那里似乎打破了这一链条。

尝试的解决方案

我尝试过：

• 设置列mainAxisSize：MainAxisSize.min

• 在“展开”（在“行”和“列”小部件之间）中包装列

• 使用LayoutBuilder创建一个SizedBox，其高度为BoxConstraints的maxHeight，用于包装列

• 使用ConstrainedBox（也用于LayoutBuilder）

代码段

Expanded(
  flex: 2,
  child: Row(
    mainAxisAlignment: MainAxisAlignment.spaceEvenly,
    crossAxisAlignment: CrossAxisAlignment.center,
    mainAxisSize: MainAxisSize.min,
    children: <Widget>[
      Column(
        mainAxisSize: MainAxisSize.min,
        children: <Widget>[
          Text('Title goes here'),
          Stack(
            alignment: Alignment.center,
            children: <Widget>[
              restWidget,
              if (!_appBarStopwatch.isRunning)
                ...startButton,
            ],
          ),
        ],
      ),
    ],
  ),
),

restWidget是一个引用类型为RestIndicator的自定义窗口小部件的变量

Expanded是以下树的“ SafeArea”>“ Padding”>“ Column”的子代。

错误

flutter: ══╡ EXCEPTION CAUGHT BY RENDERING LIBRARY ╞═════════════════════════════════════════════════════════
flutter: The following assertion was thrown during performLayout():
flutter: BoxConstraints forces an infinite width and infinite height.
.
.
.
flutter: The following RenderObject was being processed when the exception was fired:
flutter:   RenderConstrainedBox#7d17f relayoutBoundary=up10 NEEDS-LAYOUT NEEDS-PAINT
flutter:   creator: SizedBox.expand ← Stack ← LayoutBuilder ← WorkoutRestIndicator ← StreamBuilder<Duration>
flutter:   ← StreamBuilder<RestStep> ← RestIndicator ← Stack ← Column ← Row ← Expanded ← Column ← ⋯
flutter:   parentData: not positioned; offset=Offset(0.0, 0.0) (can use size)
flutter:   constraints: BoxConstraints(unconstrained)
flutter:   size: MISSING
flutter:   additionalConstraints: BoxConstraints(biggest)

从树中删除Column小部件可以解决该错误，但是我无法创建所需的设计。有没有一种方法可以重新建立约束，使其像我介绍《专栏》之前一样工作？我需要放弃使用扩展功能吗？