Flutter AppBar 的渐变背景

Question

如何将AppBar的backgroundColor设置为渐变色？

Answer 1

AppBar 默认没有这个功能。但是你可以制作一个类似 AppBar 的小部件，它将具有如下渐变背景：

  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new PreferredSize(
        child: new Container(
          padding: new EdgeInsets.only(
            top: MediaQuery.of(context).padding.top
          ),
          child: new Padding(
            padding: const EdgeInsets.only(
              left: 30.0,
              top: 20.0,
              bottom: 20.0
            ),
            child: new Text(
              'Arnold Parge',
              style: new TextStyle(
                fontSize: 20.0,
                fontWeight: FontWeight.w500,
                color: Colors.white
              ),
            ),
          ),
          decoration: new BoxDecoration(
            gradient: new LinearGradient(
              colors: [
                Colors.red,
                Colors.yellow
              ]
            ),
            boxShadow: [
              new BoxShadow(
                color: Colors.grey[500],
                blurRadius: 20.0,
                spreadRadius: 1.0,
              )
            ]
          ),
        ),
        preferredSize: new Size(
          MediaQuery.of(context).size.width,
          150.0
        ),
      ),
      body: new Center(
        child: new Text('Hello'),
      ),
    );
  }

这里boxShadow会给人一种高大上的感觉。

Answer 2

我认为您不能将渐变传递给 AppBar，因为它需要颜色而不是渐变。

但是，除了使用渐变之外，您可以创建自己的模仿 AppBar 的小部件。看一下我从 Planets-Flutter tutorial 连同下面的代码拼凑起来的这个例子。

import "package:flutter/material.dart";

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


class GradientAppBar extends StatelessWidget {

  final String title;
  final double barHeight = 50.0;

  GradientAppBar(this.title);

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

    return new Container(
      padding: EdgeInsets.only(top: statusbarHeight),
      height: statusbarHeight + barHeight,
      child: Center(
        child: Text(
          title,
          style: TextStyle(fontSize: 20.0, color: Colors.white, fontWeight: FontWeight.bold),
        ),
      ),
      decoration: BoxDecoration(
        gradient: LinearGradient(
            colors: [Colors.red, Colors.blue],
            begin: const FractionalOffset(0.0, 0.0),
            end: const FractionalOffset(0.5, 0.0),
            stops: [0.0, 1.0],
            tileMode: TileMode.clamp
        ),
      ),
    );
  }
}

希望这对您有所帮助。如果您有任何问题，请告诉我。

Answer 3

这应该可以完美运行：

return Scaffold(
  appBar: AppBar(
    title: Text(widget.title),
    flexibleSpace: Container(
      decoration: const BoxDecoration(
        gradient: LinearGradient(
          begin: Alignment.topCenter,
          end: Alignment.bottomCenter,
          colors: <Color>[Colors.black, Colors.blue]),
      ),
    ),
  ),
);

Answer 4

@Riki137 的回答很有魅力。如果有人想尝试一下，这是另一种方法。

   _appBar = AppBar();
   return PreferredSize(
     child: ShaderMask(
         child: _appBar,
        shaderCallback: (rect) {
           return ui.Gradient.linear(rect.centerLeft, rect.centerRight,
               [Colors.black, Colors.grey]);
         }),
     preferredSize: _appBar.preferredSize,
  );

Answer 5

只需将AppBar包裹在Widgets Material > Container中，使用grandient，这样就可以保留原有AppBar的属性。这是我的带有必要属性的实现。

import 'package:flutter/material.dart';

class CustomAppBar extends StatelessWidget implements PreferredSizeWidget {
  const CustomAppBar({
    Key? key,
    this.title,
    this.leading,
    this.actions,
    this.elevation = 2.0,
  }) : super(key: key);
  final Widget? title;
  final Widget? leading;
  final double elevation;
  final List<Widget>? actions;

  @override
  Widget build(BuildContext context) {
    return Material(
      elevation: elevation,
      child: Container(
        decoration: const BoxDecoration(
          gradient: RadialGradient(
            radius: 2.5,
            stops: [
              0.0,
              0.27,
              1.0,
            ],
            colors: [
              Color(0XFFB71731),
              Color(0XFFB71731),
              Color(0XFFA5004E),
            ],
          ),
        ),
        child: AppBar(
          centerTitle: true,
          leading: leading,
          elevation: 0.0,
          title: title,
          backgroundColor: Colors.transparent,
          actions: actions,
        ),
      ),
    );
  }

  @override
  Size get preferredSize => const Size.fromHeight(kToolbarHeight);
}

那么，想用就用吧

class MyPage extends StatelessWidget {
  const MyPage ({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {

        return Scaffold(
            appBar: const CustomAppBar(),
            body: Center(child:Text("My App gradient"),
        );
  }
}

Flutter AppBar 的渐变背景

Gradient Background on Flutter AppBar

flutter

dart

flutter-layout

appbar

flutter-widget