Question

我是扑朔迷离的新手，而且我正在跟踪此Udemy课程，但是当我在Windows计算机上的Android仿真器上运行应用程序时，它会在整个屏幕上显示按钮

简单的应用程序，我只是试图从用户那里获取数据，以将其存储在s文件中，然后在控制台中将其打印出来

预期结果

我的代码：-

main.dart

import 'dart:async';
import 'dart:io';

import 'package:flutter/material.dart';
import 'package:path_provider/path_provider.dart';


void main() async{

  var data = await readData();
  if(data != null){
    print(data);
  }

  runApp(
      MaterialApp(
        title: "IO",
        home: Home(),
      )
  );
}

class Home extends StatefulWidget {
  @override
  _HomeState createState() => _HomeState();
}

class _HomeState extends State<Home> {

  var _enterDataField = TextEditingController();
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("Read/Write"),
        centerTitle: true,
        backgroundColor: Colors.greenAccent,
      ),
      body: new Container(
        padding: EdgeInsets.all(13.4),
        alignment: Alignment.topCenter,
        child: ListTile(
          title: TextField(
            controller: _enterDataField,
            decoration: InputDecoration(
                labelText: "Input Something"
            ),
          ),
          subtitle: FlatButton(
            color: Colors.redAccent,
            onPressed: (){
              print("Flat button");
              writeData(_enterDataField.text);
            },
            child: new Column(
              children: <Widget>[
                Text("Save Data"),
                Padding(padding: EdgeInsets.all(14.5)),
                Text("Save data goes all"),
              ],
            ),
          ),
        ),
      ),
    );
  }
}

Future<String> get _localPath async {
  final directory = await getApplicationDocumentsDirectory();
  return directory.path; // /home/directory/
}

Future<File> get _localFile async {
  final path = await _localPath;
  return File("$path/data.txt"); // /home/directory/data.txt
}

Future<File> writeData(String message) async {
  final file = await _localFile;
  return file.writeAsString("$message");
}

Future<String> readData() async{
  try{
    final file = await _localFile;
    String data = await file.readAsString();
    return data;
  }catch(e){
    return "Nothing has been saved yet!";
  }
}

pubspec.yaml

version: 1.0.0+1

environment:
  sdk: ">=2.1.0 <3.0.0"

dependencies:
  flutter:
    sdk: flutter

  # The following adds the Cupertino Icons font to your application.
  # Use with the CupertinoIcons class for iOS style icons.
  cupertino_icons: ^0.1.2
  path_provider: ^1.1.0

运行过程中出现错误：

Launching lib\main.dart on Android SDK built for x86 in debug mode...
Initializing gradle...
Resolving dependencies...
Gradle task 'assembleDebug'...
Built build\app\outputs\apk\debug\app-debug.apk.
I/flutter ( 4904): Nothing has been saved yet!
I/Choreographer( 4904): Skipped 105 frames!  The application may be doing too much work on its main thread.
Syncing files to device Android SDK built for x86...
D/EGL_emulation( 4904): eglMakeCurrent: 0xe7085900: ver 3 1 (tinfo 0xe70839b0)
I/flutter ( 4904): ══╡ EXCEPTION CAUGHT BY RENDERING LIBRARY ╞═════════════════════════════════════════════════════════
I/flutter ( 4904): The following assertion was thrown during performLayout():
I/flutter ( 4904): not implemented
I/flutter ( 4904): 'package:flutter/src/material/input_decorator.dart': Failed assertion: line 977 pos 12: 'false'
I/flutter ( 4904): 
I/flutter ( 4904): Either the assertion indicates an error in the framework itself, or we should provide substantially
I/flutter ( 4904): more information in this error message to help you determine and fix the underlying cause.
I/flutter ( 4904): In either case, please report this assertion by filing a bug on GitHub:
I/flutter ( 4904):   https://github.com/flutter/flutter/issues/new?template=BUG.md
I/flutter ( 4904): 
I/flutter ( 4904): When the exception was thrown, this was the stack:
I/flutter ( 4904): #2      _RenderDecoration.computeDistanceToActualBaseline (package:flutter/src/material/input_decorator.dart:977:12)
I/flutter ( 4904): #3      RenderBox.getDistanceToActualBaseline.<anonymous closure> (package:flutter/src/rendering/box.dart:1672:50)
I/flutter ( 4904): #4      __InternalLinkedHashMap&_HashVMBase&MapMixin&_LinkedHashMapMixin.putIfAbsent (dart:collection/runtime/libcompact_hash.dart:281:23)
I/flutter ( 4904): #5      RenderBox.getDistanceToActualBaseline (package:flutter/src/rendering/box.dart:1672:22)
I/flutter ( 4904): #6      _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.computeDistanceToActualBaseline (package:flutter/src/rendering/proxy_box.dart:97:20)
I/flutter ( 4904): #7      RenderBox.getDistanceToActualBaseline.<anonymous closure> (package:flutter/src/rendering/box.dart:1672:50)
I/flutter ( 4904): #8      __InternalLinkedHashMap&_HashVMBase&MapMixin&_LinkedHashMapMixin.putIfAbsent (dart:collection/runtime/libcompact_hash.dart:281:23)
I/flutter ( 4904): #9      RenderBox.getDistanceToActualBaseline (package:flutter/src/rendering/box.dart:1672:22)
I/flutter ( 4904): #10     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.computeDistanceToActualBaseline (package:flutter/src/rendering/proxy_box.dart:97:20)
I/flutter ( 4904): #11     RenderBox.getDistanceToActualBaseline.<anonymous closure> (package:flutter/src/rendering/box.dart:1672:50)
I/flutter ( 4904): #12     __InternalLinkedHashMap&_HashVMBase&MapMixin&_LinkedHashMapMixin.putIfAbsent (dart:collection/runtime/libcompact_hash.dart:281:23)
I/flutter ( 4904): #13     RenderBox.getDistanceToActualBaseline (package:flutter/src/rendering/box.dart:1672:22)
I/flutter ( 4904): #14     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.computeDistanceToActualBaseline (package:flutter/src/rendering/proxy_box.dart:97:20)
I/flutter ( 4904): #15     RenderBox.getDistanceToActualBaseline.<anonymous closure> (package:flutter/src/rendering/box.dart:1672:50)
I/flutter ( 4904): #16     __InternalLinkedHashMap&_HashVMBase&MapMixin&_LinkedHashMapMixin.putIfAbsent (dart:collection/runtime/libcompact_hash.dart:281:23)
I/flutter ( 4904): #17     RenderBox.getDistanceToActualBaseline (package:flutter/src/rendering/box.dart:1672:22)
I/flutter ( 4904): #18     RenderBox.getDistanceToBaseline (package:flutter/src/rendering/box.dart:1655:27)
I/flutter ( 4904): #19     _RenderListTile._boxBaseline (package:flutter/src/material/list_tile.dart:886:16)
I/flutter ( 4904): #20     _RenderListTile.performLayout (package:flutter/src/material/list_tile.dart:945:32)
I/flutter ( 4904): #21     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter ( 4904): #22     RenderPadding.performLayout (package:flutter/src/rendering/shifted_box.dart:199:11)
I/flutter ( 4904): #23     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter ( 4904): #24     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter ( 4904): #25     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter ( 4904): #26     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter ( 4904): #27     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter ( 4904): #28     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter ( 4904): #29     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter ( 4904): #30     RenderPositionedBox.performLayout (package:flutter/src/rendering/shifted_box.dart:385:13)
I/flutter ( 4904): #31     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter ( 4904): #32     RenderPadding.performLayout (package:flutter/src/rendering/shifted_box.dart:199:11)
I/flutter ( 4904): #33     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter ( 4904): #34     MultiChildLayoutDelegate.layoutChild (package:flutter/src/rendering/custom_layout.dart:142:11)
I/flutter ( 4904): #35     _ScaffoldLayout.performLayout (package:flutter/src/material/scaffold.dart:339:7)
I/flutter ( 4904): #36     MultiChildLayoutDelegate._callPerformLayout (package:flutter/src/rendering/custom_layout.dart:212:7)
I/flutter ( 4904): #37     RenderCustomMultiChildLayoutBox.performLayout (package:flutter/src/rendering/custom_layout.dart:356:14)
I/flutter ( 4904): #38     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter ( 4904): #39     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter ( 4904): #40     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter ( 4904): #41     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter ( 4904): #42     _RenderCustomClip.performLayout (package:flutter/src/rendering/proxy_box.dart:1203:11)
I/flutter ( 4904): #43     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter ( 4904): #44     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter ( 4904): #45     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter ( 4904): #46     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter ( 4904): #47     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter ( 4904): #48     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter ( 4904): #49     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter ( 4904): #50     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter ( 4904): #51     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter ( 4904): #52     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter ( 4904): #53     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter ( 4904): #54     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter ( 4904): #55     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter ( 4904): #56     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter ( 4904): #57     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter ( 4904): #58     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter ( 4904): #59     RenderOffstage.performLayout (package:flutter/src/rendering/proxy_box.dart:2900:13)
I/flutter ( 4904): #60     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter ( 4904): #61     RenderStack.performLayout (package:flutter/src/rendering/stack.dart:510:15)
I/flutter ( 4904): #62     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter ( 4904): #63     __RenderTheatre&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter ( 4904): #64     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter ( 4904): #65     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter ( 4904): #66     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter ( 4904): #67     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter ( 4904): #68     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter ( 4904): #69     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter ( 4904): #70     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter ( 4904): #71     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter ( 4904): #72     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter ( 4904): #73     _RenderProxyBox&RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.performLayout (package:flutter/src/rendering/proxy_box.dart:104:13)
I/flutter ( 4904): #74     RenderObject.layout (package:flutter/src/rendering/object.dart:1634:7)
I/flutter ( 4904): #75     RenderView.performLayout (package:flutter/src/rendering/view.dart:147:13)
I/flutter ( 4904): #76     RenderObject._layoutWithoutResize (package:flutter/src/rendering/object.dart:1509:7)
I/flutter ( 4904): #77     PipelineOwner.flushLayout (package:flutter/src/rendering/object.dart:768:18)
I/flutter ( 4904): #78     _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding.drawFrame (package:flutter/src/rendering/binding.dart:281:19)
I/flutter ( 4904): #79     _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding&WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:686:13)
I/flutter ( 4904): #80     _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:219:5)
I/flutter ( 4904): #81     _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:990:15)
I/flutter ( 4904): #82     _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:930:9)
I/flutter ( 4904): #83     _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding.scheduleWarmUpFrame.<anonymous closure> (package:flutter/src/scheduler/binding.dart:751:7)
I/flutter ( 4904): #85     _Timer._runTimers (dart:isolate/runtime/libtimer_impl.dart:382:19)
I/flutter ( 4904): #86     _Timer._handleMessage (dart:isolate/runtime/libtimer_impl.dart:416:5)
I/flutter ( 4904): #87     _RawReceivePortImpl._handleMessage (dart:isolate/runtime/libisolate_patch.dart:171:12)
I/flutter ( 4904): (elided 3 frames from class _AssertionError and package dart:async)
I/flutter ( 4904): 
I/flutter ( 4904): The following RenderObject was being processed when the exception was fired:
I/flutter ( 4904):   _RenderListTile#c955b relayoutBoundary=up7 NEEDS-LAYOUT NEEDS-PAINT
I/flutter ( 4904):   creator: _ListTile ← MediaQuery ← Padding ← SafeArea ← Semantics ← Listener ← _GestureSemantics ←
I/flutter ( 4904):   RawGestureDetector ← GestureDetector ← InkWell ← ListTile ← Align ← ⋯
I/flutter ( 4904):   parentData: offset=Offset(0.0, 0.0) (can use size)
I/flutter ( 4904):   constraints: BoxConstraints(0.0<=w<=352.6, 0.0<=h<=668.1)
I/flutter ( 4904):   size: MISSING
I/flutter ( 4904): This RenderObject had the following descendants (showing up to depth 5):
I/flutter ( 4904):   RenderSemanticsAnnotations#30cbc relayoutBoundary=up8 NEEDS-PAINT
I/flutter ( 4904):     RenderIgnorePointer#d2ac5 relayoutBoundary=up9 NEEDS-PAINT
I/flutter ( 4904):       RenderPointerListener#95c88 relayoutBoundary=up10 NEEDS-PAINT
I/flutter ( 4904):         _RenderDecoration#d39f5 relayoutBoundary=up11 NEEDS-PAINT
I/flutter ( 4904):           RenderRepaintBoundary#7e8a4 relayoutBoundary=up12 NEEDS-PAINT
I/flutter ( 4904):           RenderTransform#6a1d0 relayoutBoundary=up12 NEEDS-PAINT
I/flutter ( 4904):           RenderConstrainedBox#bd9be relayoutBoundary=up12 NEEDS-PAINT
I/flutter ( 4904):           RenderCustomPaint#862dd NEEDS-PAINT
I/flutter ( 4904):   RenderSemanticsAnnotations#103e3 relayoutBoundary=up8 NEEDS-PAINT
I/flutter ( 4904):     _RenderInputPadding#ab3b4 relayoutBoundary=up9 NEEDS-PAINT
I/flutter ( 4904):       RenderConstrainedBox#39a4f relayoutBoundary=up10 NEEDS-PAINT
I/flutter ( 4904):         RenderPhysicalShape#32f8b relayoutBoundary=up11 NEEDS-PAINT
I/flutter ( 4904):           RenderCustomPaint#5950d relayoutBoundary=up12 NEEDS-PAINT
I/flutter ( 4904): ════════════════════════════════════════════════════════════════════════════════════════════════════
I/flutter ( 4904): Another exception was thrown: RenderBox was not laid out: _RenderListTile#c955b relayoutBoundary=up7 NEEDS-PAINT
I/flutter ( 4904): Another exception was thrown: RenderBox was not laid out: RenderPadding#a1895 relayoutBoundary=up6 NEEDS-PAINT
I/flutter ( 4904): Another exception was thrown: RenderBox was not laid out: RenderSemanticsAnnotations#9585a relayoutBoundary=up5 NEEDS-PAINT
I/flutter ( 4904): Another exception was thrown: RenderBox was not laid out: RenderPointerListener#867ef relayoutBoundary=up4 NEEDS-PAINT
I/flutter ( 4904): Another exception was thrown: 'package:flutter/src/rendering/shifted_box.dart': Failed assertion: line 314 pos 12: 'child.hasSize': is not true.
D/        ( 4904): HostConnection::get() New Host Connection established 0xce8870c0, tid 4923
D/EGL_emulation( 4904): eglMakeCurrent: 0xe569c960: ver 3 1 (tinfo 0xe447f500)

Answer 1

设置列min的mainAxisSize

Column(
              mainAxisSize: MainAxisSize.min,
              children: <Widget>[
                Text("Save Data"),
                Padding(padding: EdgeInsets.all(14.5)),
                Text("Save data goes all"),
              ],
            ),

Answer 2

使用它。

Widget _myWidget() {
  return Padding(
    padding: const EdgeInsets.all(24.0),
    child: Column(
      mainAxisSize: MainAxisSize.min,
      crossAxisAlignment: CrossAxisAlignment.start,
      children: <Widget>[
        TextField(decoration: InputDecoration(hintText: "Write Something")),
        Container(
          color: Colors.red,
          width: 200,
          height: 100,
          child: Column(children: <Widget>[
            Text("Save Data"),
            Spacer(),
            Text("Save Data goes here"),
          ],),
        ),
      ],
    ),
  );
}

Answer 3

为了工作，我不得不将代码编辑成这样

FlatButton(
              color: Colors.redAccent,
              onPressed: (){
                print("Flat button ${_enterDataField.text}");
                writeData(_enterDataField.text.toString());
              },
              child: new Column(
                children: <Widget>[
                  Text("Save Data"),
                  Padding(padding: EdgeInsets.all(14.5)),
                  FutureBuilder(
                    future: readData(),
                    builder: (BuildContext context, AsyncSnapshot<String> data){
                      if(data.hasData != null){
                        return Text(
                          data.data.toString(),
                          style: TextStyle(
                            color: Colors.white70,
                          ),
                        );
                      }else{
                        return Text("No data has been saved");
                      }
                    },
                  ),
                ],
              ),
            )

在performLayout（）期间引发了以下断言：

3 个答案: