当我创建一个下拉按钮小部件时,我得到了这个错误,说RenderFlex溢出了右边的无限像素.
源代码是：
import 'package:flutter/material.dart';
class test extends StatefulWidget {
@override
_testState createState() => _testState();
}
class _testState extends State<test> {
//gender
List<DropdownMenuItem<int>> genderList = [];
void genderLoad(){
genderList.add(new DropdownMenuItem(child: new Text("Male"),value: 1,));
genderList.add(new DropdownMenuItem(child: new Text("Female"),value: 2,));
}
//end of gender
@override
Widget build(BuildContext context) {
genderLoad();
return Scaffold(
body: new Container(
child: new Center(
child: new DropdownButton(items: genderList, onChanged: null),
),
),
);
}
}
在我构建程序后,我没有在应用程序上看到任何DropDownButton,而是在控制台上收到错误消息.
以下是错误消息：
执行热启动…
将文件同步到为x86构建的设备Android SDK …
在5,558ms重新启动应用程序.
I/flutter (15333): ══╡ EXCEPTION CAUGHT BY RENDERING LIBRARY ╞═════════════════════════════════════════════════════════
I/flutter (15333): The following assertion was thrown during performLayout():
I/flutter (15333): RenderIndexedStack object was given an infinite size during layout.
I/flutter (15333): This probably means that it is a render object that tries to be as big as possible, but it was put
I/flutter (15333): inside another render object that allows its children to pick their own size.
I/flutter (15333): The nearest ancestor providing an unbounded width constraint is:
I/flutter (15333): RenderFlex#9b57d relayoutBoundary=up7 NEEDS-LAYOUT NEEDS-PAINT
I/flutter (15333): creator: Row ← Padding ← Container ← DefaultTextStyle ← Stack ← Listener ← _GestureSemantics ←
I/flutter (15333): RawGestureDetector ← GestureDetector ← Semantics ← DropdownButton<int> ← Center ← ⋯
I/flutter (15333): parentData: offset=Offset(0.0, 0.0) (can use size)
I/flutter (15333): constraints: BoxConstraints(0.0<=w<=411.4, 0.0<=h<=683.4)
I/flutter (15333): size: MISSING
I/flutter (15333): direction: horizontal
I/flutter (15333): mainAxisAlignment: spaceBetween
I/flutter (15333): mainAxisSize: min
I/flutter (15333): crossAxisAlignment: center
I/flutter (15333): textDirection: ltr
I/flutter (15333): verticalDirection: down
I/flutter (15333): The constraints that applied to the RenderIndexedStack were:
I/flutter (15333): BoxConstraints(0.0<=w<=Infinity, 0.0<=h<=683.4)
I/flutter (15333): The exact size it was given was:
I/flutter (15333): Size(Infinity, 683.4)
I/flutter (15333): See https://flutter.io/layout/ for more information.
I/flutter (15333):
I/flutter (15333): When the exception was thrown, this was the stack:
I/flutter (15333): #0 RenderBox.debugAssertDoesMeetConstraints.<anonymous closure> (package:flutter/src/rendering/box.dart:1749:9)
I/flutter (15333): #1 RenderBox.debugAssertDoesMeetConstraints (package:flutter/src/rendering/box.dart:1823:6)
I/flutter (15333): #2 RenderBox.size=.<anonymous closure> (package:flutter/src/rendering/box.dart:1543:17)
I/flutter (15333): #3 RenderBox.size= (package:flutter/src/rendering/box.dart:1543:65)
I/flutter (15333): #4 RenderStack.performLayout (package:flutter/src/rendering/stack.dart:480:7)
I/flutter (15333): #5 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (15333): #6 RenderFlex.performLayout (package:flutter/src/rendering/flex.dart:738:15)
I/flutter (15333): #7 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (15333): #8 RenderPadding.performLayout (package:flutter/src/rendering/shifted_box.dart:199:11)
I/flutter (15333): #9 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (15333): #10 RenderStack.performLayout (package:flutter/src/rendering/stack.dart:510:15)
I/flutter (15333): #11 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (15333): #12 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter (15333): #13 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (15333): #14 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter (15333): #15 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (15333): #16 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter (15333): #17 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (15333): #18 RenderPositionedBox.performLayout (package:flutter/src/rendering/shifted_box.dart:385:13)
I/flutter (15333): #19 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (15333): #20 MultiChildLayoutDelegate.layoutChild (package:flutter/src/rendering/custom_layout.dart:142:11)
I/flutter (15333): #21 _ScaffoldLayout.performLayout (package:flutter/src/material/scaffold.dart:339:7)
I/flutter (15333): #22 MultiChildLayoutDelegate._callPerformLayout (package:flutter/src/rendering/custom_layout.dart:212:7)
I/flutter (15333): #23 RenderCustomMultiChildLayoutBox.performLayout (package:flutter/src/rendering/custom_layout.dart:356:14)
I/flutter (15333): #24 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (15333): #25 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter (15333): #26 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (15333): #27 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter (15333): #28 _RenderCustomClip.performLayout (package:flutter/src/rendering/proxy_box.dart:1188:11)
I/flutter (15333): #29 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (15333): #30 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter (15333): #31 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (15333): #32 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter (15333): #33 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (15333): #34 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter (15333): #35 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (15333): #36 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter (15333): #37 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (15333): #38 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter (15333): #39 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (15333): #40 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter (15333): #41 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (15333): #42 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter (15333): #43 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (15333): #44 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter (15333): #45 RenderOffstage.performLayout (package:flutter/src/rendering/proxy_box.dart:2881:13)
I/flutter (15333): #46 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (15333): #47 RenderStack.performLayout (package:flutter/src/rendering/stack.dart:510:15)
I/flutter (15333): #48 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (15333): #49 __RenderTheatre&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter (15333): #50 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (15333): #51 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter (15333): #52 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (15333): #53 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter (15333): #54 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (15333): #55 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter (15333): #56 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (15333): #57 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter (15333): #58 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (15333): #59 _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter (15333): #60 RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter (15333): #61 RenderView.performLayout (package:flutter/src/rendering/view.dart:147:13)
I/flutter (15333): #62 RenderObject._layoutWithoutResize (package:flutter/src/rendering/object.dart:1509:7)
I/flutter (15333): #63 PipelineOwner.flushLayout (package:flutter/src/rendering/object.dart:768:18)
I/flutter (15333): #64 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding.drawFrame (package:flutter/src/rendering/binding.dart:281:19)
I/flutter (15333): #65 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding&WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:677:13)
I/flutter (15333): #66 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:219:5)
I/flutter (15333): #67 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:990:15)
I/flutter (15333): #68 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:930:9)
I/flutter (15333): #69 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding.scheduleWarmUpFrame.<anonymous closure> (package:flutter/src/scheduler/binding.dart:751:7)
I/flutter (15333): #71 _Timer._runTimers (dart:isolate/runtime/libtimer_impl.dart:382:19)
I/flutter (15333): #72 _Timer._handleMessage (dart:isolate/runtime/libtimer_impl.dart:416:5)
I/flutter (15333): #73 _RawReceivePortImpl._handleMessage (dart:isolate/runtime/libisolate_patch.dart:171:12)
I/flutter (15333): (elided one frame from package dart:async)
I/flutter (15333):
I/flutter (15333): The following RenderObject was being processed when the exception was fired:
I/flutter (15333): RenderIndexedStack#d77d9 relayoutBoundary=up8 NEEDS-LAYOUT NEEDS-PAINT
I/flutter (15333): creator: IndexedStack ← Row ← Padding ← Container ← DefaultTextStyle ← Stack ← Listener ←
I/flutter (15333): _GestureSemantics ← RawGestureDetector ← GestureDetector ← Semantics ← DropdownButton<int> ← ⋯
I/flutter (15333): parentData: offset=Offset(0.0, 0.0); flex=null; fit=null (can use size)
I/flutter (15333): constraints: BoxConstraints(0.0<=w<=Infinity, 0.0<=h<=683.4)
I/flutter (15333): size: Size(Infinity, 683.4)
I/flutter (15333): alignment: AlignmentDirectional.centerStart
I/flutter (15333): textDirection: ltr
I/flutter (15333): fit: loose
I/flutter (15333): overflow: clip
I/flutter (15333): index: null
I/flutter (15333): This RenderObject has no descendants.
I/flutter (15333): ════════════════════════════════════════════════════════════════════════════════════════════════════
I/flutter (15333): Another exception was thrown: A RenderFlex overflowed by Infinity pixels on the right.
解决方法:
设置isExpanded: true.并给它的容器一个适当的高度(例如48),或设置isDense: true或do not pass a null onChanged event or a null list of items,但如果你想因任何原因(用户没有点击它)禁用小部件,我想设置前一个条件允许做你想做的一切.
class _testState extends State<test> {
//gender
List<DropdownMenuItem<int>> genderList = [];
void genderLoad() {
genderList.clear();
genderList.add(new DropdownMenuItem(
child: new Text("Male"),
value: 1,
));
genderList.add(new DropdownMenuItem(
child: new Text("Female"),
value: 2,
));
}
//end of gender
@override
Widget build(BuildContext context) {
genderLoad();
return Scaffold(
appBar: AppBar(
// Here we take the value from the MyHomePage object that was created by
// the App.build method, and use it to set our appbar title.
title: Text('hello'),
),
body: Container(
height: 48,
color: Colors.lightGreenAccent,
child: DropdownButton(
isDense: false,
isExpanded: true,
items: genderList,
onChanged: (selected){
print(selected);
})));
}
}
有这个打开的issue,当您在必填字段上传递空值时,DropDownButton小部件无法呈现.
以便所有这些：
> DropdownButton(items：[],onChanged：(int){})
> DropdownButton(items：genderList,onChanged：null)
> DropdownButton(items：[],onChanged：null)
有问题.解决方法是本文中显示的解决方法.
return Scaffold(
body: new Container(
width: 48,
child: new Center(
child: new DropdownButton (
isExpanded: true,
items: [],
onChanged: null
),
),
),
);
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