Flutter 延迟函数调用两次
Flutter delayed function called twice
我有一个启动器屏幕,我可以在其中检查我是否有特定数据。根据结果我显示不同的屏幕
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: LauncherScreen()
);
}
}
class LauncherScreen extends StatelessWidget {
@override
Widget build(BuildContext context) {
print("build, build");
Future.delayed(new Duration(milliseconds: 2000), () {
LocalData localData = LocalData();
localData.getCity().then((city) {
if (city != null) {
Const.city = city;
Navigator.push(
context,
MaterialPageRoute(builder: (context) => Home()),
);
} else {
Navigator.push(
context,
MaterialPageRoute(builder: (context) => SelectCities()),
);
}
});
});
return Container(
width: double.infinity,
height: double.infinity,
color: Color(GoEngColors.violet));
}
}
我的 LauncherScreen
调用了两次,结果我看到我的 Home
或 Select city
屏幕出现了两次。
出现这种行为的原因是什么,如何解决?谢谢
build
方法可以多次调用,所以不适合调用初始化过程。您应该将您的小部件转换为 StatefulWidget
(在 Android Studio 上按 Alt + Enter)并从 initState()
调用您的 Future.delayed
。像这样:
class LauncherScreen extends StatefulWidget {
@override
_LauncherScreenState createState() => _LauncherScreenState();
}
class _LauncherScreenState extends State<LauncherScreen> {
@override
void initState() {
super.initState();
print("build, build");
Future.delayed(new Duration(milliseconds: 2000), () {
LocalData localData = LocalData();
localData.getCity().then((city) {
if (city != null) {
Const.city = city;
Navigator.push(
context,
MaterialPageRoute(builder: (context) => Home()),
);
} else {
Navigator.push(
context,
MaterialPageRoute(builder: (context) => SelectCities()),
);
}
});
});
}
@override
Widget build(BuildContext context) {
return Container(width: double.infinity, height: double.infinity, color: Color(GoEngColors.violet));
}
}
我有一个启动器屏幕,我可以在其中检查我是否有特定数据。根据结果我显示不同的屏幕
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: LauncherScreen()
);
}
}
class LauncherScreen extends StatelessWidget {
@override
Widget build(BuildContext context) {
print("build, build");
Future.delayed(new Duration(milliseconds: 2000), () {
LocalData localData = LocalData();
localData.getCity().then((city) {
if (city != null) {
Const.city = city;
Navigator.push(
context,
MaterialPageRoute(builder: (context) => Home()),
);
} else {
Navigator.push(
context,
MaterialPageRoute(builder: (context) => SelectCities()),
);
}
});
});
return Container(
width: double.infinity,
height: double.infinity,
color: Color(GoEngColors.violet));
}
}
我的 LauncherScreen
调用了两次,结果我看到我的 Home
或 Select city
屏幕出现了两次。
出现这种行为的原因是什么,如何解决?谢谢
build
方法可以多次调用,所以不适合调用初始化过程。您应该将您的小部件转换为 StatefulWidget
(在 Android Studio 上按 Alt + Enter)并从 initState()
调用您的 Future.delayed
。像这样:
class LauncherScreen extends StatefulWidget {
@override
_LauncherScreenState createState() => _LauncherScreenState();
}
class _LauncherScreenState extends State<LauncherScreen> {
@override
void initState() {
super.initState();
print("build, build");
Future.delayed(new Duration(milliseconds: 2000), () {
LocalData localData = LocalData();
localData.getCity().then((city) {
if (city != null) {
Const.city = city;
Navigator.push(
context,
MaterialPageRoute(builder: (context) => Home()),
);
} else {
Navigator.push(
context,
MaterialPageRoute(builder: (context) => SelectCities()),
);
}
});
});
}
@override
Widget build(BuildContext context) {
return Container(width: double.infinity, height: double.infinity, color: Color(GoEngColors.violet));
}
}