我有一个开始和停止按钮和一个当前的状态是准备好或没有准备好。
当启动按钮被按下时,状态还没有准备好,只有在停止按钮被按下4秒后,状态才会准备好。如果在这4秒内,启动按钮被按下,我希望在停止功能将其设置为就绪后,状态马上变成 "未就绪"(所以本质上启动功能应该等待停止功能完成)。
以下是我试图解决这个问题的示例应用程序。
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
void main() {
runApp(MyApp());
}
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
home: HomePage(),
);
}
}
class HomePage extends StatefulWidget {
@override
_HomePageState createState() => _HomePageState();
}
class _HomePageState extends State<HomePage> {
@override
Widget build(BuildContext context) {
return Scaffold(
body: Column(
crossAxisAlignment: CrossAxisAlignment.stretch,
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Text(
isCurrentlyReady ? "ready" : "not ready",
textAlign: TextAlign.center,
),
if (canPressStart)
CupertinoButton(
child: Text('Start'),
onPressed: start,
)
else
CupertinoButton(
child: Text('Stop'),
onPressed: stop,
)
],
),
);
}
bool isCurrentlyReady = true;
bool canPressStart = true;
Future<bool> isReadyFuture = Future.value(true);
start() async {
setState(() {
canPressStart = false;
});
await isReadyFuture;
setState(() {
isCurrentlyReady = false;
});
//this future will never come
isReadyFuture = Future.delayed(Duration(days: 90000), () => true);
}
stop() async {
setState(() {
canPressStart = true;
});
await Future.delayed(Duration(seconds: 4));
setState(() {
isCurrentlyReady = true;
});
isReadyFuture = Future.value(true);
}
}
我怎样才能达到预期的行为?
在这里,你去。https:/codepen.iogazialankuspenNWGMYEe。
SO也要代码。给你
Object token;
bool isReady = false;
void onStart() {
setState(() {
isReady = false;
});
token = null;
}
Future<void> onStop() async {
Object myToken = Object();
token = myToken;
await Future.delayed(Duration(seconds: 4));
if (token == myToken) {
setState(() {
isReady = true;
});
token = null;
}
}