flutter - Flutter AppBar 上的渐变背景

Question

如何将backgroundColortheAppBar 设置为渐变？

Answer 1

我不相信您可以将渐变传递给 AppBar，因为它需要颜色而不是渐变。

但是，您可以创建自己的小部件来模仿 AppBar，除非使用渐变。看看我从Planets-Flutter 教程中拼凑起来的这个例子以及它下面的代码。

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
        ),
      ),
    );
  }
}

希望这可以帮助。如果您有任何问题，请告诉我。

Answer 2

AppBar 默认没有这个功能。但是您可以制作一个类似 AppBar 的小部件，该小部件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会给人一种高高在上的感觉。

Answer 3

这应该完美无缺：

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]),
      ),
    ),
  ),
);