Dart 带有常规大小导航栏的列中的材质应用程序

我想在我的整个应用程序上显示一个图像。因此，我在Main.dart文件的一列中放置了一个图像和仪表板

我的

main.dart

文件

void main() => runApp(new MyApp());

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {   
  @override
  Widget build(BuildContext context) {
      return new MaterialApp(
        home: new Scaffold(
          body: new SafeArea(
            child: Column(
              children: <Widget>[
                new Image.asset('assets/ads.png'),
                new Expanded(
                  child: Dashboard(),
                )
              ],
            ),
          ),
        ),
      );
  }
}

现在，这段代码生成如下输出

我需要普通尺寸的衣服。这个AppBar真的很大。有人能告诉我这里出了什么问题吗？

像这样做：-

import 'package:flutter/material.dart';
void main() => runApp(new MyApp());

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      debugShowCheckedModeBanner: false,
      home: new Scaffold(
        body: new SafeArea(
          child: Column(
            children: <Widget>[
              new Image.network("https://via.placeholder.com/350x100"),
              new Expanded(
                child: Dashboard(),
              )
            ],
          ),
        ),
      ),
    );
  }
}


class Dashboard extends StatefulWidget {
  @override
  _DashboardState createState() => _DashboardState();
}

class _DashboardState extends State<Dashboard> {
  @override
  Widget build(BuildContext context) {
    return  new Scaffold(
        appBar: new AppBar(title: new Text('Books')),
        body: new Container(
          child: new Center(
            child: new Text('data'),
          ),
        ),
    );
  }
}

导入“包装：颤振/材料.省道”；
void main（）=>runApp（新的MyApp（））；
类MyApp扩展了StatefulWidget{
@凌驾
_MyAppState createState（）=>\u MyAppState（）；
}
类MyAppState扩展了状态{
@凌驾
小部件构建（构建上下文）{
返回新材料PP(
debugShowCheckedModeBanner:false，
家：新脚手架(
正文：新安全区(
子：列(
儿童：[
新映像。网络（“https://via.placeholder.com/350x100"),
新扩展(
子：仪表板（），
)
],
),
),
),
);
}
}
类Dashboard扩展StatefulWidget{
@凌驾
_DashboardState createState（）=>\u DashboardState（）；
}
类_仪表板状态扩展状态{
@凌驾
小部件构建（构建上下文）{
归还新脚手架(
appBar:new appBar（标题：新文本（“书籍”），
主体：新容器(
孩子：新中心(
子项：新文本（“数据”），
),
),
);
}
}

---

尝试从仪表板状态中删除

材料应用程序
。将其设置为：
returnscaffold（………
import 'package:flutter/material.dart';
void main() => runApp(new MyApp());

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      debugShowCheckedModeBanner: false,
      home: new Scaffold(
        body: new SafeArea(
          child: Column(
            children: <Widget>[
              new Image.network("https://via.placeholder.com/350x100"),
              new Expanded(
                child: Dashboard(),
              )
            ],
          ),
        ),
      ),
    );
  }
}


class Dashboard extends StatefulWidget {
  @override
  _DashboardState createState() => _DashboardState();
}

class _DashboardState extends State<Dashboard> {
  @override
  Widget build(BuildContext context) {
    return  new Scaffold(
        appBar: new AppBar(title: new Text('Books')),
        body: new Container(
          child: new Center(
            child: new Text('data'),
          ),
        ),
    );
  }
}