Flutter-隐藏FloatingActionButton [英] Flutter - Hiding FloatingActionButton
问题描述
Flutter中是否有任何内置方法可以隐藏ListView上的FloatingActionButton并向下滚动，然后在向上滚动时显示它?
Is there any built in way in Flutter to hide a FloatingActionButton on ListView scrolling down and then showing it on scrolling up?
推荐答案
import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';
void main() {
runApp(new MyApp());
}
class MyApp extends StatelessWidget {
// This widget is the root of your application.
@override
Widget build(BuildContext context) {
return new MaterialApp(
title: 'Flutter Demo',
theme: new ThemeData(
primarySwatch: Colors.blue,
),
home: new MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
@override
_MyHomePageState createState() => new _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
int _counter = 0;
ScrollController _hideButtonController;
void _incrementCounter() {
setState(() {
_counter++;
});
}
var _isVisible;
@override
initState(){
super.initState();
_isVisible = true;
_hideButtonController = new ScrollController();
_hideButtonController.addListener((){
if(_hideButtonController.position.userScrollDirection == ScrollDirection.reverse){
if(_isVisible == true) {
/* only set when the previous state is false
* Less widget rebuilds
*/
print("**** ${_isVisible} up"); //Move IO away from setState
setState((){
_isVisible = false;
});
}
} else {
if(_hideButtonController.position.userScrollDirection == ScrollDirection.forward){
if(_isVisible == false) {
/* only set when the previous state is false
* Less widget rebuilds
*/
print("**** ${_isVisible} down"); //Move IO away from setState
setState((){
_isVisible = true;
});
}
}
}});
}
@override
Widget build(BuildContext context) {
return new Scaffold(
appBar: new AppBar(
title: new Text(widget.title),
),
body: new Center(
child: new CustomScrollView(
controller: _hideButtonController,
shrinkWrap: true,
slivers: <Widget>[
new SliverPadding(
padding: const EdgeInsets.all(20.0),
sliver: new SliverList(
delegate: new SliverChildListDelegate(
<Widget>[
const Text('I\'m dedicating every day to you'),
const Text('Domestic life was never quite my style'),
const Text('When you smile, you knock me out, I fall apart'),
const Text('And I thought I was so smart'),
const Text('And I thought I was so smart'),
const Text('And I thought I was so smart'),
const Text('And I thought I was so smart'),
const Text('And I thought I was so smart'),
const Text('And I thought I was so smart'),
const Text('And I thought I was so smart'),
const Text('And I thought I was so smart'),
const Text('And I thought I was so smart'),
const Text('And I thought I was so smart'),
const Text('And I thought I was so smart'),
const Text('And I thought I was so smart'),
const Text('And I thought I was so smart'),
const Text('And I thought I was so smart'),
const Text('And I thought I was so smart'),
const Text('And I thought I was so smart'),
const Text('And I thought I was so smart'),
const Text('And I thought I was so smart'),
const Text('And I thought I was so smart'),
const Text('And I thought I was so smart'),
const Text('And I thought I was so smart'),
const Text('And I thought I was so smart'),
const Text('And I thought I was so smart'),
const Text('And I thought I was so smart'),
const Text('And I thought I was so smart'),
const Text('And I thought I was so smart'),
const Text('And I thought I was so smart'),
const Text('And I thought I was so smart'),
const Text('And I thought I was so smart'),
const Text('And I thought I was so smart'),
const Text('And I thought I was so smart'),
const Text('And I thought I was so smart'),
const Text('And I thought I was so smart'),
const Text('And I thought I was so smart'),
const Text('And I thought I was so smart'),
const Text('I realize I am crazy'),
],
),
),
),
],
)
),
floatingActionButton: new Visibility(
visible: _isVisible,
child: new FloatingActionButton(
onPressed: _incrementCounter,
tooltip: 'Increment',
child: new Icon(Icons.add),
),
),
);
}
}
我很抱歉，如果我不使用listview，因为我不知道如何使用listview滚动.我将回答您问题的其他部分.
I apologize if I did not use listview since I do not know how to scroll with listview. I will answer the other parts of your question.
首先，您需要创建一个 scrollcontroller 来监听 scrollPostion 事件
First you need to create a scrollcontroller that will listen scrollPostion events
如果scrollcontroller设法找到 scrolldirection 向前或向后.您添加了一个将状态设置为可见的状态.
If scrollcontroller manages to find either scrolldirection forward or reverse. You add a state that set a state to visible.
绘制按钮时，将按钮包装在可见性类.您设置了可见标志，并且小部件应忽略输入命令.
When you draw the button, you wrap the button in a visibility class. You set the visible flag and the widget should ignore input commands.
我似乎无法添加到ScrollController，ScrollerPosition，ScrollDirection和Opacity的链接.我想您可以自己搜索，也可以由其他人在链接中进行编辑
I cant seem to add links to ScrollController, ScrollerPosition, ScrollDirection, and Opacity. I guess you can search it yourself or somebody else edit in the links
Edit2:使用CopsonRoad或使用可见性小部件，除非您希望在布局树中未绘制小部件
Use CopsonRoad or use visibility widget, unless you want an unpainted widget in the layout tree
Edit3:鉴于新来者仍按原样使用代码，因此我将更新代码以鼓励更好的实践.使用可见性而不是不透明度.从setState中删除io.在Flutter 1.5.4-hotfix.2上进行了测试
In light of newcomers using code as is, I would update the code to encourage better practices. Use visibility instead of Opacity. Remove io from setState. tested on Flutter 1.5.4-hotfix.2
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