我似乎无法理解问题所在。应该输出带有16个按钮的两个Text小部件。相反，我得到的是空白的空白屏幕。任何帮助将不胜感激，谢谢！
/ *我只是为了使我的问题通过而添加此内容。我真的没有什么要补充的主要问题了。 * /
import 'package:flutter/cupertino.dart';
void main() => runApp(MainScreen());
class MainScreen extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
home: SafeArea(
child: Scaffold(
body: Column(
children: <Widget>[
/* -------------------------------------------------------------------------- */
/* Display section */
/* -------------------------------------------------------------------------- */
Column(
crossAxisAlignment: CrossAxisAlignment.end,
children: <Widget>[
Container(width: double.infinity),
Text('Hello World', style: TextStyle(fontSize: 20)),
Text('I\'m smaller!')
],
),
/* -------------------------------------------------------------------------- */
/* Button section */
/* -------------------------------------------------------------------------- */
Row(
children: <Widget>[
createButtonColumn(),
createButtonColumn(),
createButtonColumn(),
createButtonColumn()
],
)
],
)
)
)
);
}
}
Column createButtonColumn() {
return Column(
children: <Widget>[
createButton(),
createButton(),
createButton(),
createButton()
],
);
}
createButton() {
return Expanded(
// flex: 1,
child: RaisedButton(
onPressed: () {
},
child: Text('Hello')
),
);
}```
Console log
----------------------
Restarted application in 3,271ms.
I/flutter ( 5199): ══╡ EXCEPTION CAUGHT BY RENDERING LIBRARY ╞═════════════════════════════════════════════════════════
I/flutter ( 5199): The following assertion was thrown during performResize():
I/flutter ( 5199): Vertical viewport was given unbounded height.
I/flutter ( 5199): Viewports expand in the scrolling direction to fill their container. In this case, a vertical
I/flutter ( 5199): viewport was given an unlimited amount of vertical space in which to expand. This situation
I/flutter ( 5199): typically happens when a scrollable widget is nested inside another scrollable widget.
I/flutter ( 5199): If this widget is always nested in a scrollable widget there is no need to use a viewport because
I/flutter ( 5199): there will always be enough vertical space for the children. In this case, consider using a Column
I/flutter ( 5199): instead. Otherwise, consider using the "shrinkWrap" property (or a ShrinkWrappingViewport) to size
I/flutter ( 5199): the height of the viewport to the sum of the heights of its children.
I/flutter ( 5199):
I/flutter ( 5199): The relevant error-causing widget was:
[38;5;248mI/flutter ( 5199): GridView[39;49m
I/flutter ( 5199):
I/flutter ( 5199): When the exception was thrown, this was the stack:
[38;5;244mI/flutter ( 5199): #0 RenderViewport.performResize.<anonymous closure>[39;49m
[38;5;244mI/flutter ( 5199): #1 RenderViewport.performResize[39;49m
[38;5;244mI/flutter ( 5199): #2 RenderObject.layout[39;49m
[38;5;244mI/flutter ( 5199): #3 RenderProxyBoxMixin.performLayout[39;49m
[38;5;244mI/flutter ( 5199): #4 RenderObject.layout[39;49m
[38;5;244mI/flutter ( 5199): #5 RenderProxyBoxMixin.performLayout[39;49m
[38;5;244mI/flutter ( 5199): #6 RenderObject.layout[39;49m
[38;5;244mI/flutter ( 5199): #7 RenderProxyBoxMixin.performLayout[39;49m
[38;5;244mI/flutter ( 5199): #8 RenderObject.layout[39;49m
[38;5;244mI/flutter ( 5199): #9 RenderProxyBoxMixin.performLayout[39;49m
[38;5;244mI/flutter ( 5199): #10 RenderObject.layout[39;49m
[38;5;244mI/flutter ( 5199): #11 RenderProxyBoxMixin.performLayout[39;49m
[38;5;244mI/flutter ( 5199): #12 RenderObject.layout[39;49m
[38;5;244mI/flutter ( 5199): #13 RenderProxyBoxMixin.performLayout[39;49m
[38;5;244mI/flutter ( 5199): #14 RenderObject.layout[39;49m
[38;5;244mI/flutter ( 5199): #15 RenderProxyBoxMixin.performLayout[39;49m
[38;5;244mI/flutter ( 5199): #16 RenderObject.layout[39;49m
[38;5;244mI/flutter ( 5199): #17 RenderProxyBoxMixin.performLayout[39;49m
[38;5;244mI/flutter ( 5199): #18 RenderObject.layout[39;49m
[38;5;244mI/flutter ( 5199): #19 RenderProxyBoxMixin.performLayout[39;49m
[38;5;244mI/flutter ( 5199): #20 RenderObject.layout[39;49m
[38;5;244mI/flutter ( 5199): #21 RenderFlex.performLayout[39;49m
[38;5;244mI/flutter ( 5199): #22 RenderObject.layout[39;49m
[38;5;244mI/flutter ( 5199): #23 RenderPadding.performLayout[39;49m
[38;5;244mI/flutter ( 5199): #24 RenderObject.layout[39;49m
[38;5;244mI/flutter ( 5199): #25 MultiChildLayoutDelegate.layoutChild[39;49m
[38;5;244mI/flutter ( 5199): #26 _ScaffoldLayout.performLayout[39;49m
[38;5;244mI/flutter ( 5199): #27 MultiChildLayoutDelegate._callPerformLayout[39;49m
[38;5;244mI/flutter ( 5199): #28 RenderCustomMultiChildLayoutBox.performLayout[39;49m
[38;5;244mI/flutter ( 5199): #29 RenderObject.layout[39;49m
[38;5;244mI/flutter ( 5199): #30 RenderProxyBoxMixin.performLayout[39;49m
[38;5;244mI/flutter ( 5199): #31 RenderObject.layout[39;49m
[38;5;244mI/flutter ( 5199): #32 RenderProxyBoxMixin.performLayout[39;49m
[38;5;244mI/flutter ( 5199): #33 _RenderCustomClip.performLayout[39;49m
[38;5;244mI/flutter ( 5199): #34 RenderObject.layout[39;49m
[38;5;244mI/flutter ( 5199): #35 RenderProxyBoxMixin.performLayout[39;49m
[38;5;244mI/flutter ( 5199): #36 RenderObject.layout[39;49m
[38;5;244mI/flutter ( 5199): #37 RenderProxyBoxMixin.performLayout[39;49m
[38;5;244mI/flutter ( 5199): #38 RenderObject.layout[39;49m
[38;5;244mI/flutter ( 5199): #39 RenderProxyBoxMixin.performLayout[39;49m
[38;5;244mI/flutter ( 5199): #40 RenderObject.layout[39;49m
[38;5;244mI/flutter ( 5199): #41 RenderProxyBoxMixin.performLayout[39;49m
[38;5;244mI/flutter ( 5199): #42 RenderObject.layout[39;49m
[38;5;244mI/flutter ( 5199): #43 RenderProxyBoxMixin.performLayout[39;49m
[38;5;244mI/flutter ( 5199): #44 RenderObject.layout[39;49m
[38;5;244mI/flutter ( 5199): #45 RenderProxyBoxMixin.performLayout[39;49m
[38;5;244mI/flutter ( 5199): #46 RenderObject.layout[39;49m
[38;5;244mI/flutter ( 5199): #47 RenderProxyBoxMixin.performLayout[39;49m
[38;5;244mI/flutter ( 5199): #48 RenderObject.layout[39;49m
[38;5;244mI/flutter ( 5199): #49 RenderProxyBoxMixin.performLayout[39;49m
[38;5;244mI/flutter ( 5199): #50 RenderOffstage.performLayout[39;49m
[38;5;244mI/flutter ( 5199): #51 RenderObject.layout[39;49m
[38;5;244mI/flutter ( 5199): #52 RenderStack.performLayout[39;49m
[38;5;244mI/flutter ( 5199): #53 RenderObject.layout[39;49m
[38;5;244mI/flutter ( 5199): #54 RenderProxyBoxMixin.performLayout[39;49m
[38;5;244mI/flutter ( 5199): #55 RenderObject.layout[39;49m
[38;5;244mI/flutter ( 5199): #56 RenderProxyBoxMixin.performLayout[39;49m
[38;5;244mI/flutter ( 5199): #57 RenderObject.layout[39;49m
[38;5;244mI/flutter ( 5199): #58 RenderProxyBoxMixin.performLayout[39;49m
[38;5;244mI/flutter ( 5199): #59 RenderObject.layout[39;49m
[38;5;244mI/flutter ( 5199): #60 RenderProxyBoxMixin.performLayout[39;49m
[38;5;244mI/flutter ( 5199): #61 RenderObject.layout[39;49m
[38;5;244mI/flutter ( 5199): #62 RenderProxyBoxMixin.performLayout[39;49m
[38;5;244mI/flutter ( 5199): #63 RenderObject.layout[39;49m
[38;5;244mI/flutter ( 5199): #64 RenderProxyBoxMixin.performLayout[39;49m
[38;5;244mI/flutter ( 5199): #65 RenderObject.layout[39;49m
[38;5;244mI/flutter ( 5199): #66 RenderProxyBoxMixin.performLayout[39;49m
[38;5;244mI/flutter ( 5199): #67 RenderObject.layout[39;49m
[38;5;244mI/flutter ( 5199): #68 RenderView.performLayout[39;49m
[38;5;244mI/flutter ( 5199): #69 RenderObject._layoutWithoutResize[39;49m
[38;5;244mI/flutter ( 5199): #70 PipelineOwner.flushLayout[39;49m
[38;5;244mI/flutter ( 5199): #71 RendererBinding.drawFrame[39;49m
[38;5;244mI/flutter ( 5199): #72 WidgetsBinding.drawFrame[39;49m
[38;5;244mI/flutter ( 5199): #73 RendererBinding._handlePersistentFrameCallback[39;49m
[38;5;244mI/flutter ( 5199): #74 SchedulerBinding._invokeFrameCallback[39;49m
[38;5;244mI/flutter ( 5199): #75 SchedulerBinding.handleDrawFrame[39;49m
[38;5;244mI/flutter ( 5199): #76 SchedulerBinding.scheduleWarmUpFrame.<anonymous closure>[39;49m
[38;5;244mI/flutter ( 5199): #85 _Timer._runTimers (dart:isolate-patch/timer_impl.dart:384:19)[39;49m
[38;5;244mI/flutter ( 5199): #86 _Timer._handleMessage (dart:isolate-patch/timer_impl.dart:418:5)[39;49m
[38;5;244mI/flutter ( 5199): #87 _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:174:12)[39;49m
I/flutter ( 5199): (elided 8 frames from package dart:async and package dart:async-patch)
I/flutter ( 5199):
I/flutter ( 5199): The following RenderObject was being processed when the exception was fired: RenderViewport#9f404 NEEDS-LAYOUT NEEDS-PAINT NEEDS-COMPOSITING-BITS-UPDATE:
I/flutter ( 5199): needs compositing
I/flutter ( 5199): creator: Viewport ← IgnorePointer-[GlobalKey#317b3] ← Semantics ← _PointerListener ← Listener ←
I/flutter ( 5199): _GestureSemantics ← RawGestureDetector-[LabeledGlobalKey<RawGestureDetectorState>#d3688] ←
I/flutter ( 5199): _PointerListener ← Listener ← _ScrollableScope ← _ScrollSemantics-[GlobalKey#d8d85] ←
I/flutter ( 5199): RepaintBoundary ← ⋯
I/flutter ( 5199): parentData: <none> (can use size)
I/flutter ( 5199): constraints: BoxConstraints(0.0<=w<=411.4, 0.0<=h<=Infinity)
I/flutter ( 5199): size: MISSING
I/flutter ( 5199): axisDirection: down
I/flutter ( 5199): crossAxisDirection: right
I/flutter ( 5199): offset: ScrollPositionWithSingleContext#a94d8(offset: 0.0, range: null..null, viewport: null,
I/flutter ( 5199): ScrollableState, AlwaysScrollableScrollPhysics -> ClampingScrollPhysics, IdleScrollActivity#cbf73,
I/flutter ( 5199): ScrollDirection.idle)
I/flutter ( 5199): anchor: 0.0
I/flutter ( 5199): This RenderObject had the following descendants (showing up to depth 5):
I/flutter ( 5199): center child: RenderSliverPadding#a6421 NEEDS-LAYOUT NEEDS-PAINT NEEDS-COMPOSITING-BITS-UPDATE
I/flutter ( 5199): child: RenderSliverGrid#b12d1 NEEDS-LAYOUT NEEDS-PAINT
I/flutter ( 5199): ════════════════════════════════════════════════════════════════════════════════════════════════════
I/flutter ( 5199): Another exception was thrown: RenderBox was not laid out: RenderViewport#9f404 NEEDS-LAYOUT NEEDS-PAINT NEEDS-COMPOSITING-BITS-UPDATE
I/flutter ( 5199): Another exception was thrown: RenderBox was not laid out: RenderViewport#9f404 NEEDS-PAINT NEEDS-COMPOSITING-BITS-UPDATE
I/flutter ( 5199): Another exception was thrown: RenderBox was not laid out: RenderIgnorePointer#4f70f relayoutBoundary=up11 NEEDS-PAINT NEEDS-COMPOSITING-BITS-UPDATE
I/flutter ( 5199): Another exception was thrown: RenderBox was not laid out: RenderSemanticsAnnotations#63f8a relayoutBoundary=up10 NEEDS-PAINT NEEDS-COMPOSITING-BITS-UPDATE
I/flutter ( 5199): Another exception was thrown: RenderBox was not laid out: RenderPointerListener#05d0a relayoutBoundary=up9 NEEDS-PAINT NEEDS-COMPOSITING-BITS-UPDATE
I/flutter ( 5199): Another exception was thrown: RenderBox was not laid out: RenderSemanticsGestureHandler#cd528 relayoutBoundary=up8 NEEDS-PAINT NEEDS-COMPOSITING-BITS-UPDATE
I/flutter ( 5199): Another exception was thrown: RenderBox was not laid out: RenderPointerListener#821d7 relayoutBoundary=up7 NEEDS-PAINT NEEDS-COMPOSITING-BITS-UPDATE
I/flutter ( 5199): Another exception was thrown: RenderBox was not laid out: _RenderScrollSemantics#2700b relayoutBoundary=up6 NEEDS-PAINT NEEDS-COMPOSITING-BITS-UPDATE
I/flutter ( 5199): Another exception was thrown: RenderBox was not laid out: RenderRepaintBoundary#99506 relayoutBoundary=up5 NEEDS-PAINT NEEDS-COMPOSITING-BITS-UPDATE
I/flutter ( 5199): Another exception was thrown: RenderBox was not laid out: RenderCustomPaint#af2b0 relayoutBoundary=up4 NEEDS-PAINT NEEDS-COMPOSITING-BITS-UPDATE
I/flutter ( 5199): Another exception was thrown: RenderBox was not laid out: RenderRepaintBoundary#3e297 relayoutBoundary=up3 NEEDS-PAINT NEEDS-COMPOSITING-BITS-UPDATE
I/flutter ( 5199): Another exception was thrown: RenderBox was not laid out: RenderFlex#5c063 relayoutBoundary=up2 NEEDS-PAINT NEEDS-COMPOSITING-BITS-UPDATE
I/flutter ( 5199): Another exception was thrown: RenderBox was not laid out: RenderPadding#b3df3 relayoutBoundary=up1 NEEDS-PAINT NEEDS-COMPOSITING-BITS-UPDATE
I/flutter ( 5199): Another exception was thrown: NoSuchMethodError: The method '>' was called on null.
答案 0 :(得分：2)
如果用扩展包装行，它将非常有效。
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
void main() => runApp(MainScreen());
class MainScreen extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
home: SafeArea(
child: Scaffold(
body: Column(
crossAxisAlignment: CrossAxisAlignment.stretch,
children: <Widget>[
/* -------------------------------------------------------------------------- */
/* Display section */
/* -------------------------------------------------------------------------- */
Column(
crossAxisAlignment: CrossAxisAlignment.end,
children: <Widget>[
Container(width: double.infinity),
Text('Hello World', style: TextStyle(fontSize: 20)),
Text('I\'m smaller!')
],
),
/* -------------------------------------------------------------------------- */
/* Button section */
/* -------------------------------------------------------------------------- */
Expanded(
child: Row(
mainAxisSize: MainAxisSize.max,
children: <Widget>[
createButtonColumn(),
createButtonColumn(),
createButtonColumn(),
createButtonColumn()
],
),
)
],
))));
}
}
Widget createButtonColumn() {
return Expanded(
child: Column(
crossAxisAlignment: CrossAxisAlignment.stretch,
children: <Widget>[
createButton(),
createButton(),
createButton(),
createButton()
],
),
);
}
createButton() {
return Expanded(
// flex: 1,
child: RaisedButton(onPressed: () {}, child: Text('Hello')),
);
}
答案 1 :(得分：2)
尝试以下代码：您应该使用 Flexible 或 Expanded 小部件来包装 Column 和 Row 小部件。拥有孩子财产的一方。
import 'package:flutter/material.dart';
void main() => runApp(MainScreen());
class MainScreen extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
home: SafeArea(
child: Scaffold(
body:Body()
)
)
);
}
}
class Body extends StatelessWidget {
@override
Widget build(BuildContext context) {
var size =MediaQuery.of(context).size;
return Column(
children: <Widget>[
/* -------------------------------------------------------------------------- */
/* Display section */
/* -------------------------------------------------------------------------- */
Column(
crossAxisAlignment: CrossAxisAlignment.end,
mainAxisSize:
MainAxisSize.min,
children: <Widget>[
Container(width: double.infinity),
Text('Hello World', style: TextStyle(fontSize: 20)),
Text('I\'m smaller!')
],
),
/* -------------------------------------------------------------------------- */
/* Button section */
/* -------------------------------------------------------------------------- */
Expanded(
child: Row(mainAxisSize:
MainAxisSize.min,
children: <Widget>[
createButtonColumn(),
createButtonColumn(),
createButtonColumn(),
createButtonColumn()
],
),
)
],
);
}
}
Column createButtonColumn() {
return Column(mainAxisSize:
MainAxisSize.min,
children: <Widget>[
createButton(),
createButton(),
createButton(),
createButton()
],
);
}
createButton() {
return Expanded(
// flex: 1,
child: RaisedButton(
onPressed: () {
},
child: Text('Hello')
),
);
}