展开 Flutter 中的应用栏以允许 Multi-Line 标题？

Question

有谁知道如何根据此处显示的 material 指南创建带有 multi-line 标题的应用栏？

https://material.io/design/components/app-bars-top.html#anatomy

有什么办法吗？鉴于它是 material 指南的一部分，它似乎应该很简单！值得指出的是，标题是用户定义的，所以我希望允许应用栏根据用户输入从单行扩展到多行（可能有限制）。

麦克

Answer 1

这还没有实现。

不过，您可以使用为 CustomScrollView 设计的 SliverAppBar 来获得类似的结果。

请记住，这并不是最佳选择。因为它需要硬编码图标和东西的大小。由于 FlexibleSpacebar 没有宽度限制。

import 'package:flutter/material.dart';
import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:flutter_project/materialSheet.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Flutter Demo',
      theme: new ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: new MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => new _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: CustomScrollView(
        slivers: <Widget>[
          SliverMultilineAppBar(
            title: "Summer Trip to Tokyo and Kyoto",
            leading: IconButton(
              onPressed: () {},
              icon: Icon(Icons.menu),
            ),
            actions: <Widget>[
              IconButton(
                onPressed: () {},
                icon: Icon(Icons.search),
              ),
              IconButton(
                onPressed: () {},
                icon: Icon(Icons.more_vert),
              ),
            ],
          ),
        ],
      ),
    );
  }
}

class SliverMultilineAppBar extends StatelessWidget {
  final String title;
  final Widget leading;
  final List<Widget> actions;

  SliverMultilineAppBar({this.title, this.leading, this.actions});

  @override
  Widget build(BuildContext context) {
    final mediaQuery = MediaQuery.of(context);

    double availableWidth = mediaQuery.size.width - 160;
    if (actions != null) {
      availableWidth -= 32 * actions.length;
    }
    if (leading != null) {
      availableWidth -= 32;
    }
    return SliverAppBar(
      expandedHeight: 120.0,
      forceElevated: true,
      leading: leading,
      actions: actions,
      flexibleSpace: FlexibleSpaceBar(
        title: ConstrainedBox(
          constraints: BoxConstraints(
            maxWidth: availableWidth,
          ),
          child: Text(title, textScaleFactor: .8,),
        ),
      ),
    );
  }
}

Answer 2

AppBar 会让您接近这个，但是您必须根据您的文本长度指示底部 PreferredSize 小部件的高度，这并不理想。

@override
Widget build(BuildContext context) {
  return Scaffold(
    appBar: AppBar(
      backgroundColor: Colors.deepPurple,
      leading: IconButton(icon: Icon(Icons.menu), onPressed: () {}),
      actions: <Widget>[
        IconButton(icon: Icon(Icons.search), onPressed: () {}),
        IconButton(icon: Icon(Icons.more_vert), onPressed: () {}),
      ],
      bottom: PreferredSize(
        child: Padding(
          padding: const EdgeInsets.fromLTRB(80.0, 0.0, 80.0, 16.0),
          child: Text(
            "Summer Trip to Tokyo and Kyoto",
            style: TextStyle(
              color: Colors.white,
              fontSize: 24.0,
            ),
          ),
        ),
        preferredSize: Size(0.0, 80.0),
      ),
    ),
    body: Text("..."),
  );
}

Answer 3

您可以使用 RichText：

          SliverAppBar(
        flexibleSpace: FlexibleSpaceBar(
          background: Container(
            color: Colors.indigoAccent,
          ),
          title: RichText(
            text: TextSpan(children: [
              TextSpan(
                text: Constants.homePageTitle,
                style: textTheme.headline,
              ),
              TextSpan(text: "\n"),
              TextSpan(
                text: Constants.homePageSubtitle,
                style: textTheme.subtitle,
              )
            ]),
          ),
          titlePadding: EdgeInsets.only(left: 10, bottom: 20),
        ),
        floating: true,
        backgroundColor: Colors.greenAccent,
        expandedHeight: 150.0,
      ),

Answer 4

将AppBar的"title"属性换成"flexibleSpace"即可实现：

  Scaffold(
    appBar: AppBar(
      flexibleSpace: Center(
        child: Column(
          children: [
            Text('Title Line One'),
            Text('Title Line Two'),
          ],
        ),
      ),
    ),
    body: body
  ),

如果由于高度而发生溢出，只需用 PreferredSize 小部件包裹 AppBar 并将高度设置为比默认值更高的值：

  Scaffold(
    appBar: PreferredSize(
      preferredSize: Size.fromHeight(100),
      child: AppBar(...),
    ),
  ),

Answer 5

试试下面的代码。这将提供多行，您还可以在其中控制文本样式。如果您不希望所有行都使用不同的样式，请使用 Text 而不是 RichText。

             AppBar(
                title: RichText(
                  textAlign: TextAlign.center,
                  text: TextSpan(
                      text: "Developer Developer",
                      style: TextStyle(fontSize: 20),
                      children: <TextSpan>[
                        TextSpan(
                          text: '\nTrip List',
                          style: TextStyle(
                            fontSize: 16,
                          ),
                        ),
                      ]
                  ),
                ),
                backgroundColor: MissionGPSTheme.themeBlueColor
            ),

Answer 6

这段代码将创建一个带有 AppBar 的自定义 Scaffold，支持接收无标题、有标题、有标题和副标题。如果您不提供标题，它将显示给定的文本（在示例中为应用程序的名称），而如果您设置了标题和副标题，它将使用带有适当 Material设计文字样式。

import 'package:flutter/material.dart';

class TwoLinesAppBarScaffold extends StatelessWidget {
  final Widget body;
  final String title;
  final String subtitle;

  TwoLinesAppBarScaffold({this.body, this.title = "QuitNow!", this.subtitle});

  @override
  Widget build(BuildContext context) {
    Widget widget;

    if (subtitle == null) {
      widget = Text(title);
    } else {
      widget = RichText(
        textAlign: TextAlign.start,
        text: TextSpan(
            text: title,
            style: TextStyle(
              fontSize: 20,
              fontWeight: FontWeight.w500,
            ),
            children: <TextSpan>[
              TextSpan(
                text: '\n$subtitle',
                style: TextStyle(
                  fontSize: 16,
                  fontWeight: FontWeight.normal,
                ),
              ),
            ]),
      );
    }

    return Scaffold(
        appBar: AppBar(
          title: widget,
        ),
        body: Center(child: body));
  }
}

展开 Flutter 中的应用栏以允许 Multi-Line 标题？

Expand The App bar in Flutter to Allow Multi-Line Title?

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flutter-layout