I could not understand why my screen build was being executed when popping. I narrowed it down to this line:
final String userId = ModalRoute.of(context).settings.arguments;
Why does the screen rebuild? How should I stop it rebuilding, or bail out when it happens?
Here is a complete example, with counter-example:
https://dartpad.dev/9f83473a923e39e9c4b07840bc4aded7
The problem seems to be know by now, but no actual fixes have actually been found somehow (or so it seems).
It is discussed here : https://github.com/flutter/flutter/issues/63364
As well as here : https://github.com/flutter/flutter/issues/35575
Generally, the accepted solutions seem to either :
Pass the arguments to the page directly through parameters of the page class (see 'vivek yadav' answers).
Retrieve the arguments in the initState() method and directly inside addPostFrameCallback() (see code below) rather than in the build() or didChangeDependencies() methods.
#override
void initState() {
super.initState();
WidgetsBinding.instance.addPostFrameCallback((timeStamp) {
final args = ModalRoute.of(context).settings.arguments;
print(args);
});
}
However, I am still very interested to know if you found another solution or actual fix to this issue. Currently, I am using the 1st solution I listed above but I am not quite satisfied with it to be honest.
We pass a class object in MaterialPageRoute for eg
Navigator.of(context).push(
MaterialPageRoute(
builder: (ctx) => ScreenWithoutArg(),
),
);
Sometimes, we need to send data while routing, also in some cases class is selected dynamically.
In such a scenario, If we add data implementation in class constructor then it's not a good coding practice.
Rather than we can pass the same data in RouteSettings.
// suggested
Navigator.of(context).push(
MaterialPageRoute(
builder: (ctx) => ScreenWithArg(),
settings: RouteSettings(arguments: 'Arg'),
),
);
// not suggested (Prone to code changes)
Navigator.of(context).push(
MaterialPageRoute(
builder: (ctx) => ScreenWithArg(arg1: 'argdata',arg2:'agrdata2'),
settings: RouteSettings(arguments: 'Arg'),
),
);
Thanks, #Patrick O'Hara for highlighting this stunning feature of the dart.
I dont get complatly your question but if you want to delete or pop before navigator
Navigator.of(context).push(
MaterialPageRoute(
builder: (ctx) => ScreenWithArg(),
settings: RouteSettings(arguments: 'Arg'),
),
);
instead use this line code
Navigator.of(context).pushReplacement(
MaterialPageRoute(
builder: (ctx) => ScreenWithArg(),
settings: RouteSettings(arguments: 'Arg'),
),
);
Related
I have been wrestling with this issue for a couple of days now and I haven't been able to find a solution, hence the post.
At one point in my app, I need to pop 2 routes from the navigator stack and push a new route. After researching the best way to do this, I have found that using pushNamedAndRemoveUntil is the best way, as I can specify ModalRoute.withName('/<route_name>') and it will pop the routes until it reaches /<route_name> at which point it will stop and push the new route. This is the line I have been using Navigator.of(context).pushNamedAndRemoveUntil('/raceadmin_reporting', ModalRoute.withName('/raceadmin_page'));.
My issue though is that it doesn't work for me. It doesn't seem to matter what I put in /<route_name>, pushNamedAndRemoveUntil pops all the routes, which leads me to believe that ModalRoute.withName never returns true.
I have also tried Navigator.of(context).pushNamedAndRemoveUntil('/raceadmin_reporting', (route) => route == RaceAdminPage.route()); and it doesn't work either.
When I look at the debugger, this is what I see:
App Navigator Stack
The route I am trying to pop until is the RaceAdmin page, which is clearly in the stack. In the definition of that class, I added the line static const routeName = '/raceadmin_page'; which is what I call in ModalRoute.withName('/raceadmin_name') and it doesn't work.
My routes are defined in the routes.dart file as per below:
static Route<dynamic> generateRoute(RouteSettings settings) {
switch (settings.name) {
case '/':
return MaterialPageRoute(builder: (context) => RailMeatApp());
case '/raceadmin_page':
return MaterialPageRoute(builder: (context) => const RaceAdminPage());
case '/raceadmin_pendinglist':
return MaterialPageRoute(builder: (context) => PendingResultsList());
case '/raceadmin_pendingresults':
final args = settings.arguments as Map<String?, String?>;
return MaterialPageRoute(
builder: (context) => PendingResultsPage(
raceId: args['raceId'] as String,
));
case '/raceadmin_reporting':
return MaterialPageRoute(builder: (context) => RaceAdminReporting());
default:
return _errorRoute();
}
}
And my MaterialApp is defined as per below:
return MaterialApp(
navigatorKey: _navigatorKey,
home: _railmeatHome(),
onGenerateRoute: RailmeatRoutes.generateRoute,
);
}
In the Flutter debugger, I can look at the MaterialApp widget and I can see in its state that the navigator has 4 entries in its _history property as shown below:
MaterialApp Widget Properties
If I click on any of the entries in the _history, I see the the same info as below:
Route property in _history
As you can see, the name property under _settings is null, which, in my mind, would explain why ModalRoute.withName can't find the right route, but I am not sure that my thinking is accurate.
What should I do differently to make pushNamedAndRemoveUntil work?
Thanks a lot in advance,
Bertrand.
Try this instead
Navigator.of(context)
.pushNamedAndRemoveUntil('/routename', (Route<dynamic> route) => false);
Or
Navigator.of(context).popUntil(ModalRoute.withName('/root'));
How can we reuse same widget with the same state, just building it once, and rebuilding only on changes at app state model (obviously currently it is being rebuilt each time when I trigger the Navigator)?
Navigator.of(context).push( MaterialPageRoute(
builder: (context) => SchedulerView(), ), );
SchedulerView is the target widget.
Thank you.
I'm guessing that your issue is not the rebuild (which is a call of the build() function triggered by the framework) but the creation of another SchedulerView instance because the Navigator calls the constructor SchedulerView()...?
If so, can you achieve your objective by instantiating only once and then using it by reference?
var schedulerView = SchedulerView();
...
Navigator.of(context).push( MaterialPageRoute( builder: (_) => schedulerView));
This is my code
Widget homeDashBoardCards(title, image, BuildContext context) {
return GestureDetector(
onTap: () => Navigator.push(
context,
MaterialPageRoute(
builder: (context) => DashBoardScreen(),
),
),
);
}
and I need to just be able to change this context to chose the page, instead of creating a lot of Widgets.
homeDashBoardCards('Categories', 'chii-icon.png', context),
like creating 2 cases or more in this one...
builder: (context) => DashBoardScreen
Just as an example:
builder: (context) => case "1" = DashBoardScreen
case "2" = FavoriteScreen
Thank you guys...
1. What I think the Problem Is
What you want is not 100% clear from the question, but I think you simply want a function that would have a switch inside returning which page the user should go to?
In that case, you might want to check out:
Flutter's tutorials on routing
switch statement in Dart
2. One Possible Solution
Create a switch function for deciding which page to switch to. Instead of using Strings, I highly suggest using enums. But both are possible.
enum Screens {dashboard, favorite}
Widget screenSwitcher(Screens screenEnum) {
switch (screenEnum) {
case Screens.dashboard:
return DashBoardScreen();
case Screens.favorite:
return FavoriteScreen();
default:
throw Exception;
}
}
Note that, if you have a non-empty case clause ending with a return, throw or continue, you don't need a break. The default clause doesn't need a break.
Return the screen when routing by calling the switcher function — you can obviously create more parameters for the functions, if necessary —:
Widget homeDashBoardCards(title, image, Screens screenEnum, BuildContext context) {
return GestureDetector(
onTap: () => Navigator.push(
context,
MaterialPageRoute(
builder: (context) => screenSwitcher(screenEnum),
),
),
);
}
3. Further Reading
Your code will be much simpler and easier to read if you use Named Routing, as mentioned in the first section of this answer. Additionally, if routing is very important to your app and complicated, you might want to consider looking for or creating a package in the pub.dev package host.
If you accept the solution code I shared above, you're passing variables through different widgets, which is not very object-oriented and also not the Flutter way. You should then consider state sharing packages to work around that. Two of the most notable ones are the BLoC and the Provider packages, but you can also do it with rxdart and the get_it package, check this video by Fireship for a great summary.
I have created NavigationDrawer in flutter before navigation drawer screen appear to user I have 3 screen before it
splash screen
intro slider
Login screen
NavigationDrawer
I want to close my app when user press back button in android phone from navigationdrawer screen but it will shows black screen.
I have called below called for navigation from login to drawer
Navigator.pushAndRemoveUntil(
context,
MaterialPageRoute(
builder: (BuildContext context) => NavigationDrawerDemo(),
),
ModalRoute.withName('/LoginFieldForm'));
I called loginfieldform with
Navigator.push(context,
new MaterialPageRoute(builder: (context) =>new LoginFieldForm()));
I think you have pushed the "LoginFieldForm" with the Navigator.push method and trying to remove it using the named routes.
For Ex :
// Puching a route with Navigator.push method
Navigator.push(
context,
MaterialPageRoute(builder: (context) => LoginFieldForm()),
);
// Removing using the named routes.
Navigator.pushAndRemoveUntil(
context,
MaterialPageRoute(
builder: (BuildContext context) => NavigationDrawerDemo(),
),
ModalRoute.withName('/LoginFieldForm'));
You can only use ModalRoute.withName() if you have added the route using named routes.
Your route probably has not a name set. If so, popping until the name is matched will result in popping everything, since the name you're looking for will never be found.
When you push LoginFieldForm ensure to pass a settings to the Route.
When pushing, you can do this:
MaterialPageRoute(
settings: RouteSettings(name: "routeName"),
builder: (context) => YourWidget(),
)
If you're within onGenerateRoute you already have settings passed as an argument to the onGenerateRoute function. In that case, just forward them to the MaterialPageRoute:
MaterialPageRoute(
settings: settings, //these settings are arguments from the function
builder: (context) => YourWidget(),
)
To close the app you may use exit(0) of dart:io on back press.exit(0) help out to Exit the Dart VM process immediately with the given exit code.
This does not wait for any asynchronous operations to terminate. You may find more information about exit(0) here
Or
SystemChannels.platform.invokeMethod('SystemNavigator.pop');
For more detail you may check here
Use-case: pushNamedAndRemoveUntil
Navigator.of(context).pushNamedAndRemoveUntil('/LoginFieldForm',
(Route<dynamic> route) => false);
I cannot understand the reason why someone should use named routes, with Navigator.pushNamed(), instead of the normal way with Navigator.push().
The tutorial page states that:
if we need to navigate to the same screen in many parts of our apps,
this can result in code duplication. In these cases, it can be handy
to define a “named route,” and use the named route for Navigation
Duplication
How will the duplication be generated when using simple routing and how it will can be eliminated with the use of named routes?
I fail to understand what is the difference of
Navigator.push(
context,
MaterialPageRoute(builder: (context) => SecondRoute()),
);
from
Navigator.pushNamed(context, '/second');
in the context of duplication.
Consider you go with Navigator.push() in many widgets:
// inside widget A:
Navigator.push(
context,
MaterialPageRoute(builder: (context) => SecondRoute()),
);
// inside widget B:
Navigator.push(
context,
MaterialPageRoute(builder: (context) => SecondRoute()),
);
// inside widget C:
Navigator.push(
context,
MaterialPageRoute(builder: (context) => SecondRoute()),
);
Now let say you need to change your App and the widget SecondRoute needs to receive a value on it's constructor. Now you have a problem, since you have multiple copies of the same code on several locations, you need to make sure you will update all of those copies, which can be tedious and error prone:
// inside widget A:
Navigator.push(
context,
MaterialPageRoute(builder: (context) => SecondRoute(
title: 'Title A',
)),
);
// inside widget B:
Navigator.push(
context,
MaterialPageRoute(builder: (context) => SecondRoute(
title: 'Title B',
)),
)),
);
// inside widget C:
Navigator.push(
context,
MaterialPageRoute(builder: (context) => SecondRoute(
title: 'Title A', // ERROR! Forgot to change the variable after a copy/paste
)),
)),
);
Now let's consider you go with named routes.
Firstly I would never recommend anyone to actually use the name directly for navigation, but instead use a static variable reference, this way if you need to change it in the future its way simpler and secure, as you can't forget to update it anywhere, like this:
class Routes {
static const String second = '/second';
}
Another way is to have a reference inside the route itself, a static const String inside SecondRoute, so we can use it as SecondRoute.routeName. It's a matter of personal preference IMO.
Then your widgets will navigate using:
// inside widget A:
Navigator.pushNamed(context, Routes.second); // Routes.second is the same as '/second'
// inside widget B:
Navigator.pushNamed(context, Routes.second);
// inside widget C:
Navigator.pushNamed(context, Routes.second);
Now if you need to pass a parameter to SecondRoute upon creation you can do it in a centralized location using the MaterialApp onGenerateRoute, as this tutorial explains in more detail. Your code will be changed to:
// inside widget A:
Navigator.pushNamed(context, Routes.second, arguments: 'Title A');
// inside widget B:
Navigator.pushNamed(context, Routes.second, arguments: 'Title B');
// inside widget C:
// You can still make mistakes here, but the chances are smaller.
Navigator.pushNamed(context, Routes.second, arguments: 'Title C');
MaterialApp(
onGenerateRoute: (settings) {
if (settings.name == Routes.second) {
final String title = settings.arguments;
return MaterialPageRoute(
builder: (context) => SecondRoute(title: title),
);
}
},
);
The amount of duplicated code is decreased, but on the other hand the onGenerateRoute code gets more complex as you make more routes, as all of their creation will be centralized there, so IMHO it's more about a personal preference then a general guideline.
Push and PushNamed have the similar effect, Push will switch to the route you specified while PushNamed will switch to the route with the route name specified.
What the Tutorial page means for duplication is duplication of code not duplication of routes.
For instance, you have a route where you would want to check whether the user is signed in and show the corresponding page
Using Push only:
Page1:
//This is page 1....
RaisedButton(
child: Text('Go to second'),
onPressed: () {
if (user.state = "login") {
Navigator.of(context).push(
MaterialPageRoute(
builder: (context) => SecondPage(),
),
)
}else{
Navigator.of(context).push(
MaterialPageRoute(
builder: (context) => SecondPageAnonymous(),
),
)
}
}
)
....
In another page, Page2, you will need to repeat the same code:
//This is page 2....
RaisedButton(
child: Text('Go to second'),
onPressed: () {
if (user.state = "login") {
Navigator.of(context).push(
MaterialPageRoute(
builder: (context) => SecondPage(),
),
)
}else{
Navigator.of(context).push(
MaterialPageRoute(
builder: (context) => SecondPageAnonymous(),
),
)
}
}
)
....
With PushNamed, you just have to declare it once and you can basically reuse it over and over again.
In your onGenerateRoute:
onGenerateRoute: (settings) {
switch (settings.name) {
case '/':
return MaterialPageRoute(builder: (_) => FirstPage());
case '/second':
if (user.state = "login") {
return MaterialPageRoute(
builder: (_) => SecondPage()
);
}else{
return MaterialPageRoute(
builder: (_) => SecondPageAnonymous()
);
}
default:
return _errorRoute();
}
},
Now in ANY pages in your project, you could do this:
Navigator.of(context).pushNamed('/second')
Without needing to repeat the checking of sign in or even the error handling every time you used it. The obvious benefit is that you can stay consistent throughout the app by preventing duplicate code piece, instead of repeating it again and again.
Now, this however DOES NOT prevent duplicates of routes! There is no different between push and pushNamed in this context!
But since your routes are now named, you can do popUntil('/') easily to go back to the first instance of the route, instead of creating it again or PushReplacementNamed.
The only advantage I can see using Navigate with named routes is to have routes declared inside your MaterialApp, so that developer can only be used assigned routes i.e widgets, pages,
If anyone uses other than that, It will give an error 'onUnknownRoute is called.'
Here is my beginner flutter thoughts:
It makes the code cleaner: Without declaring the routes at the level higher widgets, new screens will appear out of nowhere, in response to anything that happens in the app. It is much easier to understand the navigation skeleton/ structure when you declare the routes together, and even more so at a higher widget, especially for other developers. Of course, this doesn't help with understanding exactly when those routes are actually navigated to, but its a small improvement, and brings us back into the declarative paradigm. The hint provided by the declared routes will help a newer developer understand your navigation flow.
For folks visiting this question in 2022. Flutter actually now recommends not using named routes
Note: Named routes are no longer recommended for most applications. For more information, see Limitations in the navigation overview page.
https://docs.flutter.dev/cookbook/navigation/named-routes
If you use push(), you have to import the file in which SecondRoute is located every time you need to navigate to that screen. This is excessive code duplication for big projects that you need to navigate around the different screens.
If you use pushNamed(), you need to define the routes only once in your MaterialApp. Then, you can navigate to any screen from anywhere without repeating the same thing like you have to with push().
Another big reason to choose PushNamed() over the other one is to be able to build your own navigation system with it. You can decide whether or not routes are available for certain users even before they navigate to the screen.
for understanding why we should use Navigator.pushNamed instead Navigator.push first let's be familiar with Navigator methods. did you ever heart about Navigator.popUntil or Navigator.pushAndRemoveUntil?
we use Navigator.popUntil when we want to pop in the stack to a specific route. if you check the documentation you can find that it's very easy to use these methods with the pushNamed method. also, check all methods in the documentation. when I try to understand routing in flutter this article was very useful for me.
and as a disadvantage, it's very hard to handle parameters in this approach. you should create onGenerateRoute and handle parameters for each route.