Flutter: Setting the height of the AppBar

问题:

How can I simply set the height of the AppBar in Flutter?

The title of the bar should be staying centered vertically (in that AppBar).

回答1:

You can use PreferredSize:

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Example',
      home: Scaffold(
        appBar: PreferredSize(
          preferredSize: Size.fromHeight(50.0), // here the desired height
          child: AppBar(
            // ...
          )
        ),
        body: // ...
      )
    );
  }
}

回答2:

You can use PreferredSize and flexibleSpace for it:

appBar: PreferredSize(
  preferredSize: Size.fromHeight(100.0),
  child: AppBar(
    automaticallyImplyLeading: false, // hides leading widget
    flexibleSpace: SomeWidget(),
  )
),

This way you can keep the elevation of AppBar for keeping its shadow visible and have custom height, which is what I was just looking for. You do have to set the spacing in SomeWidget, though.

回答3:

At the time of writing this, I was not aware of PreferredSize. Cinn's answer is better to achieve this.

You can create your own custom widget with a custom height:

import "package:flutter/material.dart";

class Page extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new Column(children : <Widget>[new CustomAppBar("Custom App Bar"), new Container()],);
  }
}


class CustomAppBar extends StatelessWidget {

  final String title;
  final double barHeight = 50.0; // change this for different heights 

  CustomAppBar(this.title);

  @override
  Widget build(BuildContext context) {
    final double statusbarHeight = MediaQuery
        .of(context)
        .padding
        .top;

    return new Container(
      padding: new EdgeInsets.only(top: statusbarHeight),
      height: statusbarHeight + barHeight,
      child: new Center(
        child: new Text(
          title,
          style: new TextStyle(fontSize: 20.0, fontWeight: FontWeight.bold),
        ),
      ),
    );
  }
}

回答4:

In addition to @Cinn's answer, you can define a class like this

class MyAppBar extends AppBar with PreferredSizeWidget {
  @override
  get preferredSize => Size.fromHeight(50);

  MyAppBar({Key key, Widget title}) : super(
    key: key,
    title: title,
    // maybe other AppBar properties
  );
}

or this way

class MyAppBar extends PreferredSize {
  MyAppBar({Key key, Widget title}) : super(
    key: key,
    preferredSize: Size.fromHeight(50),
    child: AppBar(
      title: title,
      // maybe other AppBar properties
    ),
  );
}

and then use it instead of standard one

回答5:

If you are in Visual Code, Ctrl + Click on AppBar function.

Widget demoPage() {
  AppBar appBar = AppBar(
    title: Text('Demo'),
  );
  return Scaffold(
    appBar: appBar,
    body: /*
    page body
    */,
  );
}

And edit this piece.

app_bar.dart will open and you can find 
    preferredSize = new Size.fromHeight(kToolbarHeight + (bottom?.preferredSize?.height ?? 0.0)),

Difference of height!