I am new to Getx's dependency injection, so can some one explain to me the benefits of Get.put() and Get.lazyPut() and tell me also what difference they have?
Short answer
Get.put() will put immediately
Get.lazyPut() will put when you need it
To my understanding put already puts an instance of the class directly in memory while lazyPut just puts a builder for it in it.
A benefit of lazyPut is that it saves memory until you actually find it. And you can also put more complex code in the builder for it. Another benefit of lazyPut is that you can also say fenix: true on it which means it's able to be reconstructed in case it got disposed of before.
I would think the only benefit of using put is that find should be slightly faster then when called because it doesn't need to call a builder first to get the instance. I don't know if there are other benefits.
In the case of lazyPut, it only creates the instance, and it'll be instantiated only when is used, check more details here
Get.put() :
Will inject a dependency and start executing immediately when it's injected, and I mean with that that its lifecycle methods like onInit() and onReady() will execute when you inject it like this:
class ControllerOne extends GetxController {
int a = 1;
#override
void onInit() {
print('ControllerOne onInit');
super.onInit();
}
#override
void onReady() {
print('ControllerOne onReady');
super.onReady();
}
}
final controller = Get.put(ControllerOne()); // will inject that dependecy, and immediately will call onInit() method then onReady() method
Debug log:
ControllerOne onInit
ControllerOne onReady
Get.lazyPut() :
will also inject a dependency, but it will not start executing the lifecycle methods onInit() and onReady() until you will really use that controller:
class ControllerTwo extends GetxController {
int b = 2;
#override
void onInit() {
print('ControllerTwo onInit');
super.onInit();
}
#override
void onReady() {
print('ControllerTwo onReady');
super.onReady();
}
}
final controller = Get.lazyPut(() => ControllerTwo()); // will inject that dependecy, and wait until it's used then it will call onInit() method, then onReady() method
Debug log:
/* nothing will be printed right now */
but if we do use the controller, as an example:
controller.b = 10;
then the controller will start running will start:
Debug log:
ControllerTwo onInit
ControllerTwo onReady
Hope this clarifies it!
Related
Im using getx and i want to call api after bage build, because this api its not necessary part of the page build.. What i know is this way
#override
void initState(){
super.initState();
WidgetsBinding.instance.addPostFrameCallback((_){
});
}
But what about getx best way ?
the Getx package offers lifecycle methods that are very convenient in you're cases, what you need here is to use the onReady(), which is called one frame after the onInit() is executed, you can say that its equivalent to the:
#override
void initState(){
super.initState();
WidgetsBinding.instance.addPostFrameCallback((_){
// Here is the code which will be executed exactly after initState using StatefulWidget
});
}
you can use onReady() like this:
class TextController extends GetxController {
#override
void onInit() {
/*...*/
}
void onReady() {
// Here is the code which will be executed exactly after onInit using Getx
}
}
I have a method called getData() which used to load data from API,
and i am displaying data in a separate screen, I have one issue which whenever I navigate to this page it rebuild the whole screen and call the API again and again.
PS: I'm using getX Obx to control the UI
Question: how to call the function only when new data has added
class CategoryPageBinding extends Bindings {
#override
void dependencies() {
Get.put(CategoryPageController(), permanent: true);
}
}
class CategoryPageController extends GetxController {
#override
void onInit() {
super.onInit();
getAllCategories();
}
}
You can call the method in Controller using getX.
#override
void onInit() {
super.onInit();
getData();
}
what is the difference between running a method before super.initState() and after super.initState()
#override
void initState() {
super.initState();
getCurrentUser();
}
#override
void initState() {
getCurrentUser();
super.initState();
}
Explanation for framework: Dart is class based object oriented programming language, so when you build a widget you extend it from a base class StatelessWidget or StatefulWidget. initState is lifecycle method in flutter widget (as you might know) which is only available to override in StatefulWidgets and it called only once. So, it call initState of base class which is StatefulWidget thats why you call super.initState()which in turn creates BuildContext and attached State.
Now your question: I didn't find anything different in calling a method before or after super.initState(). Event I tried adding addPostFrameCallback before super.initState() and it worked fine.
Even super.mounted is also true in both cases.
Suggestion
Dart/Flutter documentation "suggests" to call super.initState() as first method before your body implementation.
But if we look at how it is implemented Documentation
#protected
#mustCallSuper
void initState() {
assert(_debugLifecycleState == _StateLifecycle.created);
}
it's possible to see that it contains only an assert(). the assert built-in function it's called only in DEBUG mode, not in production mode. So, at the end of the day, it really doesn't matter, because the super.initState() would practically do nothing.
I really miss C programming. Flutter is quite confusing.
Here is the problem:
We have a function within the Stateful class Home. That creates a page called myMenu.
class Home extends StatefulWidget {
myMenu createState() => myMenu();
}
class myMenu extends State<Home>
{
void myProblemFunction(String stringItem) async {
final db = await myDatabaseClass.instance.database;
...
}
Whenever myProblemFunction runs, it will instantiate a new database instance.
I just want to put this command once (i.e.:
final db = await myDatabaseClass.instance.database
) anywhere in my document (this is my main.dart file (by the way). Now, I could put it in the initState() - sure.. but that's a headache, because a) I would have to make it async, and I feel that will cause me problems, and b) declaring final db... (etc) in the initState() will not make the db variable visible to my functions.
What do I do?
what are the elements in myMenu Class that are triggered? Should I put this function inside the widget build method? But surely if the widget is refreshed, then this function will also be called (again) - I just want to call it once.
Thanks
you can use FutureBuilder
example:
FutureBuilder(
future: myDatabaseClass.instance.database,
builder: (BuildContext context,AsycnSnapshot snapshot){
//your code here
},
)
this will only load the Future once when the widget is built.
put your code that you want to run only once in initState():
#override
void initState() {
super.initState();
// TODO code you want to run only once
}
I'm currently trying Provider as a state management solution, and I understand that it can't be used inside the initState function.
All examples that I've seen call a method inside a derived ChangeNotifier class upon user action (user clicks a button, for example), but what if I need to call a method when initialising my state?
Motivation:
Creating a screen which loads assets (async) and shows progress
An example for the ChangeNotifier class (can't call add from initState):
import 'package:flutter/foundation.dart';
class ProgressData extends ChangeNotifier {
double _progress = 0;
double get progress => _progress;
void add(double dProgress) {
_progress += dProgress;
notifyListeners();
}
}
You can call such methods from the constructor of your ChangeNotifier:
class MyNotifier with ChangeNotifier {
MyNotifier() {
someMethod();
}
void someMethod() {
// TODO: do something
}
}
Change your code to this
class ProgressData extends ChangeNotifier {
double _progress = 0;
double get progress => _progress;
void add(double dProgress) async {
// Loading Assets maybe async process with its network call, etc.
_progress += dProgress;
notifyListeners();
}
ProgressData() {
add();
}
}
In initState all the of(context) things don't work correctly, because the widget is not fully wired up with every thing in initState.
You can use this code:
Provider.of<ProgressData>(context, listen: false).add(progress)
Or this code:
Future.delayed(Duration.zero).then(_){
Provider.of<ProgressData>(context).add(progress)
}):
So an AssetLoader class which reports on its progress will look something like this, I guess:
import 'package:flutter/foundation.dart';
class ProgressData extends ChangeNotifier {
double _progress = 0;
ProgressData() {
_loadFake();
}
Future<void> _loadFake() async {
await _delayed(true, Duration(seconds: 1));
_add(1.0);
await _delayed(true, Duration(seconds: 2));
_add(2.0);
await _delayed(true, Duration(seconds: 3));
_add(3.0);
}
// progress
double get progress => _progress;
// add
void _add(double dProgress) {
_progress += dProgress;
notifyListeners();
}
// _delayed
Future<dynamic> _delayed(dynamic returnVal, Duration duration) {
return Future.delayed(duration, () => returnVal);
}
}
As Fateme said:
the widget is not fully wired up with everything in initState
Also, you can use something like this in your initState
WidgetsBinding.instance?.addPostFrameCallback((timeStamp) {
Provider.of<ProgressData>(context, listen: false).add(5);
});
I think it's more standard!
Be aware that you should use the correct context! I mean the context of the Builder!
The problem here lies with the fact that context does not exist yet in initState as extensively explained by the other answers. It doesn't exist because it hasn't yet been made a part of the widget tree.
Calling a method
If you're not assigning any state and only calling a method then initState would be the best place to get this done.
// The key here is the listen: false
Provider.of<MyProvider>(context, listen: false).mymethod();
The code above is allowed by Flutter because it doesn't have to listen for anything. In short, it's a one off. Use it where you only want to do something instead of read/listen to something.
Listening to changes
Alternatively, if you need to listen to changes from Provider then the use of didChangeDependencies would be the best place to do so as context would exist here as in the docs.
This method is also called immediately after initState.
int? myState;
#override
void didChangeDependencies() {
// No listen: false
myState = Provider.of<MyProvider>(context).data;
super.didChangeDependencies();
}
If you've never used didChangeDependencies before, what it does is get called whenever updateShouldNotify() returns true. This in turn lets any widgets that requested an inherited widget in build() respond as needed.
I'd usually use this method in a FutureBuilder to prevent reloading data when data already exists in Provider after switching screens. This way I can just check Provider for myState and skip the preloader (if any) entirely.
Hope this helps.