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flutter - Flutter：SingleChildScrollView 沿垂直轴收缩其子项错误

问题描述

在 Scaffold 我有一个容器来设置 background 。在容器的孩子中，我有SingleChildScrollView，在它的孩子中，我有Column. 在这个小部件的孩子中，我有 2Expanded个小部件：

Scaffold
    |
     Container
        |
         SingleChildScrollView
            |
             * Expanded
             * Expanded

这是代码：

 Widget build(BuildContext context) {
    return Scaffold(
      extendBodyBehindAppBar: true,
      resizeToAvoidBottomPadding: true,
      body: Container(
          decoration: BoxDecoration(
            image: DecorationImage(
              image: AssetImage("images/main_background.png"),
              fit: BoxFit.cover,
            ),
          ),
          child: SingleChildScrollView(
            child: Column(
              mainAxisAlignment: MainAxisAlignment.start,
              children: <Widget>[
                Expanded(..)
                Expanded(..)

我的问题是当在这个页面上运行时，所有页面都有粉红色意味着我收到了这个错误：

I/flutter ( 8893): ══╡ EXCEPTION CAUGHT BY RENDERING LIBRARY ╞═════════════════════════════════════════════════════════
I/flutter ( 8893): The following assertion was thrown during performLayout():
I/flutter ( 8893): RenderFlex children have non-zero flex but incoming height constraints are unbounded.
I/flutter ( 8893): When a column is in a parent that does not provide a finite height constraint, for example if it is
I/flutter ( 8893): in a vertical scrollable, it will try to shrink-wrap its children along the vertical axis. Setting a
I/flutter ( 8893): flex on a child (e.g. using Expanded) indicates that the child is to expand to fill the remaining
I/flutter ( 8893): space in the vertical direction.
I/flutter ( 8893): These two directives are mutually exclusive. If a parent is to shrink-wrap its child, the child
I/flutter ( 8893): cannot simultaneously expand to fit its parent.
I/flutter ( 8893): Consider setting mainAxisSize to MainAxisSize.min and using FlexFit.loose fits for the flexible
I/flutter ( 8893): children (using Flexible rather than Expanded). This will allow the flexible children to size
I/flutter ( 8893): themselves to less than the infinite remaining space they would otherwise be forced to take, and
I/flutter ( 8893): then will cause the RenderFlex to shrink-wrap the children rather than expanding to fit the maximum
I/flutter ( 8893): constraints provided by the parent.
I/flutter ( 8893): If this message did not help you determine the problem, consider using debugDumpRenderTree():
I/flutter ( 8893):   https://flutter.dev/debugging/#rendering-layer
I/flutter ( 8893):   http://api.flutter.dev/flutter/rendering/debugDumpRenderTree.html
I/flutter ( 8893): The affected RenderFlex is:
I/flutter ( 8893):   RenderFlex#4b35c relayoutBoundary=up13 NEEDS-LAYOUT NEEDS-PAINT NEEDS-COMPOSITING-BITS-UPDATE(creator: Column ← _SingleChildViewport ← IgnorePointer-[GlobalKey#fcff2] ← Semantics ← _PointerListener ← Listener ← _GestureSemantics ← RawGestureDetector-[LabeledGlobalKey<RawGestureDetectorState>#e245d] ← _PointerListener ← Listener ← _ScrollableScope ← _ScrollSemantics-[GlobalKey#471e6] ← ⋯, parentData: <none> (can use size), constraints: BoxConstraints(0.0<=w<=320.0, 0.0<=h<=Infinity), size: MISSING, direction: vertical, mainAxisAlignment: start, mainAxisSize: max, crossAxisAlignment: center, verticalDirection: down)
I/flutter ( 8893): The creator information is set to:
I/flutter ( 8893):   Column ← _SingleChildViewport ← IgnorePointer-[GlobalKey#fcff2] ← Semantics ← .....

问题是什么？

标签： flutterflutter-layout

解决方案

  • Expanded 会根据父Column的box约束展开
  • 看起来 SingleChildScrollView 正在将无限高度约束传递给 Column 并且 Expanded 试图扩展到无限。

尝试用 Container 或 ConstrainedBox 包裹 Column 并传递有限高度。为了了解更多，我写了一篇关于为什么会发生这种情况的文章。

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