老师你好，我在PhotoApp中build外层加了MaterialApp会报错

Question

老师你好，我在PhotoApp中build如下代码：
如果 没有 children: _getImages(),就可以运行，添加后会报错
麻烦可以帮我看下为什么会报那个错误么？
代码如下：
return MaterialApp(
title: ‘这是一个相机APP的demo’,
theme: ThemeData(backgroundColor: Colors.white),
home: Scaffold(
appBar: AppBar(
title: Text(‘相机APP的demo’),
leading: GestureDetector(
onTap: () {
Navigator.pop(context);
},
child: Icon(Icons.arrow_back),
),
),
body: Center(
child: Wrap(
spacing: 5,
runSpacing: 5,
children: _getImages(),
)),
floatingActionButton: FloatingActionButton(
onPressed: _pickImage(),
tooltip: ‘选择图片’,
child: Icon(Icons.add_a_photo),
),
),
);

错误如下：
Syncing files to device AOSP on HammerHead…
I/flutter (16585): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
I/flutter (16585): The following assertion was thrown building PhotoApp(dirty, dependencies:
I/flutter (16585): [_LocalizationsScope-[GlobalKey#69ffc], _InheritedTheme], state: _PhotoAppState#21835):
I/flutter (16585): setState() or markNeedsBuild() called during build.
I/flutter (16585): This Overlay widget cannot be marked as needing to build because the framework is already in the
I/flutter (16585): process of building widgets. A widget can be marked as needing to be built during the build phase
I/flutter (16585): only if one of its ancestors is currently building. This exception is allowed because the framework
I/flutter (16585): builds parent widgets before children, which means a dirty descendant will always be built.
I/flutter (16585): Otherwise, the framework might not visit this widget during this build phase.
I/flutter (16585): The widget on which setState() or markNeedsBuild() was called was:
I/flutter (16585): Overlay-[LabeledGlobalKey#bf2f4](state: OverlayState#992e6(tickers: tracking 1
I/flutter (16585): ticker, entries: [OverlayEntry#f93c3(opaque: false; maintainState: false),
I/flutter (16585): OverlayEntry#c4a28(opaque: false; maintainState: true), OverlayEntry#2fddd(opaque: false;
I/flutter (16585): maintainState: false), OverlayEntry#ac5f2(opaque: false; maintainState: true),
I/flutter (16585): OverlayEntry#c9481(opaque: false; maintainState: false), OverlayEntry#d8035(opaque: false;
I/flutter (16585): maintainState: true)]))
I/flutter (16585): The widget which was currently being built when the offending call was made was:
I/flutter (16585): PhotoApp(dirty, dependencies: [_LocalizationsScope-[GlobalKey#69ffc], _InheritedTheme], state:
I/flutter (16585): _PhotoAppState#21835)
I/flutter (16585): When the exception was thrown, this was the stack:
I/flutter (16585): #0 Element.markNeedsBuild. (package:flutter/src/widgets/framework.dart:3497:11)
I/flutter (16585): #1 Element.markNeedsBuild (package:flutter/src/widgets/framework.dart:3523:6)
I/flutter (16585): #2 State.setState (package:flutter/src/widgets/framework.dart:1138:14)
I/flutter (16585): #3 OverlayState.insertAll (package:flutter/src/widgets/overlay.dart:301:5)
I/flutter (16585): #4 OverlayRoute.install (package:flutter/src/widgets/routes.dart:43:24)
I/flutter (16585): #5 TransitionRoute.install (package:flutter/src/widgets/routes.dart:184:11)
I/flutter (16585): #6 ModalRoute.install (package:flutter/src/widgets/routes.dart:899:11)
I/flutter (16585): #7 NavigatorState.push (package:flutter/src/widgets/navigator.dart:1672:11)
I/flutter (16585): #8 Navigator.push (package:flutter/src/widgets/navigator.dart:1011:34)

Answer 1

CrazyCodeBoy 2019-04-22 21:30:55

参考下：

import 'dart:io';

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

///【实战尝鲜】拍照APP开发
class PhotoApp extends StatefulWidget {
  @override
  _PhotoAppState createState() => _PhotoAppState();
}

class _PhotoAppState extends State<PhotoApp> {
  List<File> _images = [];

  Future getImage(bool isTakePhoto) async {
    Navigator.pop(context);
    var image = await ImagePicker.pickImage(
        source: isTakePhoto ? ImageSource.camera : ImageSource.gallery);

    setState(() {
      _images.add(image);
    });
  }

  @override
  Widget build(BuildContext context) {
    return
      MaterialApp(
        home: Scaffold(
          appBar: AppBar(
            title: Text('【实战尝鲜】拍照APP开发'),
            leading: GestureDetector(
              onTap: () {
                Navigator.pop(context);
              },
              child: Icon(Icons.arrow_back),
            ),
          ),
          body: Center(
            child: Wrap(
              spacing: 5,
              runSpacing: 5,
              children: _genImages(),
            ),
          ),
          floatingActionButton: FloatingActionButton(
            onPressed: _pickImage,
            tooltip: '选择图片',
            child: Icon(Icons.add_a_photo),
          ),
        ),
      );
  }

  _pickImage() {
    showModalBottomSheet(
        context: context,
        builder: (context) => Container(
              height: 160,
              child: Column(
                children: <Widget>[
                  _item('拍照', true),
                  _item('从相册选择', false),
                ],
              ),
            ));
  }

  _item(String title, bool isTakePhoto) {
    return GestureDetector(
      child: ListTile(
        leading: Icon(isTakePhoto ? Icons.camera_alt : Icons.photo_library),
        title: Text(title),
        onTap: () => getImage(isTakePhoto),
      ),
    );
  }

  _genImages() {
    return _images.map((file) {
      return Stack(
        children: <Widget>[
          ClipRRect(
            //圆角效果
            borderRadius: BorderRadius.circular(5),
            child: Image.file(file, width: 120, height: 90, fit: BoxFit.fill),
          ),
          Positioned(
              right: 5,
              top: 5,
              child: GestureDetector(
                onTap: () {
                  setState(() {
                    _images.remove(file);
                  });
                },
                child: ClipOval(
                  //圆角删除按钮
                  child: Container(
                    padding: EdgeInsets.all(3),
                    decoration: BoxDecoration(color: Colors.black54),
                    child: Icon(
                      Icons.close,
                      size: 18,
                      color: Colors.white,
                    ),
                  ),
                ),
              ))
        ],
      );
    }).toList();
  }
}

• 提问者 qq_雪儿_19 #1

  48行的 _pickImage没有加括号，导致点击icon弹不出来底层弹框，加上括号也还是报错昨天那个。我是用Nexus5真机测试的，有关系么？

• CrazyCodeBoy 回复 提问者 qq_雪儿_19 #2

  没关系，如果还是有问题的话，可以讲下老师好友：1586866509，我帮你远程调试下