如何在不使用appbar的bottom属性且不增加appbar高度的情况下将线性进度条放置在appbar底部?
就像下面的图片:Material design appbar
为什么不想使用bottom属性?这就是Flutter AppBar
小部件提供的用于在其中添加内容的钩子。否则,您必须创建自己的AppBar
版本。
如果对您有用,我在下面创建了您可以在您的应用栏中使用的代码段。
appBar: new AppBar(
title: new Text("Title"),
backgroundColor: Colors.orange,
bottom: MyLinearProgressIndicator(
backgroundColor: Colors.orange,
),
),
MyLinearProgressIndicator
必须实现preferredSize
getter。因此,您需要创建自己的版本。
// Cant't use _kLinearProgressIndicatorHeight 'cause it is private in the
// progress_indicator.dart file
const double _kMyLinearProgressIndicatorHeight = 6.0;
class MyLinearProgressIndicator extends LinearProgressIndicator
implements PreferredSizeWidget {
MyLinearProgressIndicator({
Key key,
double value,
Color backgroundColor,
Animation<Color> valueColor,
}) : super(
key: key,
value: value,
backgroundColor: backgroundColor,
valueColor: valueColor,
) {
preferredSize = Size(double.infinity, _kMyLinearProgressIndicatorHeight);
}
@override
Size preferredSize;
}
这是结果:
@@ chemamolins的答案是完全正确的,但是仅将小部件包装在Preferred Size小部件中可能会更容易。小部件带有child
和preferredSize
类型的Size
。这是我正在处理的应用程序的一个示例,包装了StreamBuilder:
return Scaffold(
appBar: AppBar(
bottom: PreferredSize(
preferredSize: Size(double.infinity, 1.0),
child: ProgressBar(widget.bloc.isLoading),
),
---snip---
class ProgressBar extends StatelessWidget {
final Stream<bool> _isLoading;
ProgressBar(this._isLoading);
@override
Widget build(BuildContext context) {
return StreamBuilder(
stream: _isLoading,
builder: (context, snapshot) {
if (snapshot.hasData && snapshot.data) {
return LinearProgressIndicator();
}
else {
return Container();
}
}
);
}
}
只需将LinearProgressIndicator()
用作column
中的第一个小部件。然后,您将在Appbar
return Scaffold(
appbar: Appbar(
title: Text('App Bar'),),
body: Column(
children: <widget> [
linearProgressIndicator(),
Text('Hi'),]
),
)
Chemamolins' answer是正确的,但是我觉得LinearProgressIndicator
的厚度比应该的要厚一些。我的版本:
AppBar(
title: Text("Title"),
bottom: _AppBarProgressIndicator()
);
班级:
const double _kAppBarProgressIndicatorHeight = 4.0;
class _AppBarProgressIndicator extends SizedBox implements PreferredSizeWidget {
AppBarProgressIndicator({ Key key }) : super(
key: key,
height: _kAppBarProgressIndicatorHeight,
child: LinearProgressIndicator()
);
@override
Size get preferredSize => Size(
double.infinity,
_kAppBarProgressIndicatorHeight
);
}
AppBar(
title: Text("Title"),
bottom: _createProgressIndicator()
);
方法:
PreferredSize _createProgressIndicator() => PreferredSize(
preferredSize: Size(double.infinity, 4.0),
child: SizedBox(
height: 4.0,
child: LinearProgressIndicator()
)
);
完整代码在这里,
appBar的高度设置为首选大小。
在线测试:https://dartpad.dartlang.org/flutter
import 'package:flutter/material.dart';
void main() {
runApp(MyApp());
}
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
debugShowCheckedModeBanner: false,
home: Scaffold(
body: Center(
child: HomePage(),
),
),
);
}
}
class HomePage extends StatefulWidget {
HomePage({Key key}) : super(key: key);
@override
_HomePageState createState() => _HomePageState();
}
class _HomePageState extends State<HomePage> {
bool contactingServer = true; // change this as needed and call setState afterwards
@override
Widget build(BuildContext context) {
return SafeArea(
child: Scaffold(
appBar: appBarWgt(),
body: Container(),
),
);
}
appBarWgt() {
double appBarHeight = 56;
double progressBarHeight = 5;
return PreferredSize(
preferredSize: Size.fromHeight(appBarHeight + progressBarHeight), // here the desired height
child: AppBar(
title: Text('Home'),
titleSpacing: 0,
centerTitle: true,
bottom: linearProgressBar(progressBarHeight),
),
);
}
linearProgressBar(_height) {
if (!contactingServer) {
return null;
}
return PreferredSize(
child: SizedBox(
width: double.infinity,
height: _height,
child: LinearProgressIndicator(),
),
preferredSize: const Size.fromHeight(0),
);
}
}
我希望这会有所帮助,
谢谢