I have a screen with two widgets, one has a button the other one has a bottom sheet function.
I want to invoke the bottom sheet function from the other widget the problem is that my bottom sheet function needs context which makes it must be invoked inside the build function. I can invoke any function using a voidcallback on widget 1 which has the button and a constructor method on widget 2 but I need context to invoke this function. How is it possible to achieve that?
just make your method accept a BuildContext context as parameter, then when you call it you can pass the context of the widget that makes the call.
Related
I have stateful widget that is basically list of tasks. In that widget i also have a button that causes Dialog box to appear.
Dialog box is AlertDialog that consists of text field that has controller inside of it and Save button. Button calls state's method that does few things:
dialog box to pop so to get back to list of tasks
causes setState of stateful widget with value from controller
controller to clear
Method looks like this:
void saveNewTask() {
Navigator.of(context).pop();
setState(() {
toDoList.add([_controller.text, false]);
});
_controller.clear();
}
This method is passed all the way down to Save button, and Dialog box is of course seperate widget so Navigator gets the right context.
Considering the order in saveNewTask i would assume the order would go like this:
Dialog box gets poped off
setState gets called, stateful widget gets rebuild
controller is cleared.
but in slow motion i can see this operations don't happen in this order. Controller is cleared and widget is rebuilt before navigator pops off dialog box.
Before cliking the Save Button : -
After clicking the Save Button : -
(and after the second picture dialog box gets removed)
Digging through source code i found out that pop causes another setState of navigator's state that removes the Dialog box.
I thought that maybe popis asynchronous considering the behavior but Future is not returned so i can't use asynchronous function or thento enforce the order. setState is of course not asynchronous so i don't have a clue what's happening here??
Any clue is greatly appreciated.
The procedure you're following is not the actual way to do it.
Reasons:
AlertDialogue and the other dialogues you show are not a part of your main screen widget. It's a totally different widget. So you can't actually setState() of your widget from here.
Now you're trying to set the state of the dialogue widget which is already being removed when you say Navigator.pop();. Which is not possible. Cz that widget doesn't exist anymore.
In normal situations that controller would get destroyed too with the alert widget. But it's a good practice to manually destroy it.
So, to do it the right way these are the steps you should follow ->
First return the controller value to the main widget by passing it to the Navigator.pop(); function. In your case, just pass it for the save button value. Like this:
Navigator.pop(context, controller.text);
Now await on the showDialogue() method. And receive the value to the main widget. Something like this.
String? data = await showDialog(
context: context,
builder: (context) => AlertDialog());
Now in the main widget check if the dialogue returns a string or not. If it does, then set the state with the data you just received. And if it doesn't. In your case, when the cancel button is clicked. It will return null. Then don't do anything.
And finally, if you want to clear the controller for some reason. Then clear it before popping. And if you want to dispose it. Just dispose it inside the dispose method of your stateful widget.
I have a screen as statefull widget. When I instance it I have the same "this" in initState and build methods, as expected.
But if, from that screen, I open a new screen and than I come back to the first screen, first the statefull widget screen doesn't appear to be reinstanced, the method initState is not called again but the method build is called (as expected, the screen has to be drawed again) and it has a new "this" than the first time the screen has been displayed.
I could also accept the screen class has a new this but how is it possibile without a new instance of the screen widget?
It seems the class change its "this" without a new instance of the class.
Is it possibile? Why? Am I wrong?
By documents of flutter's stateful initstate
Called when this object is inserted into the tree.
The framework will call this method exactly once for each State object it creates.
Which means when you added the stateful widget for the first time this method is called and this (instance) is created..
Now the build method is called on various situations
The framework calls this method in a number of different situations. For example:
After calling initState.
After calling didUpdateWidget.
After receiving a call to setState.
After a dependency of this State object changes (e.g., an InheritedWidget referenced by the previous build changes).
After calling deactivate and then reinserting the State object into the tree at another location.
So each timethe build is called a new instance is created if you have added the code to create an instance in build method.
When you move to the next page the first screen is still in widget tree. Then you pop screen 2 so you see screen1 ahain but this time its not added to the widget tree so only the build is called.. if you do navigator.push from screen 2 and navigate to screen 1 you will see initstate being called again because a new instance of screen1 is added to the widget tree..
Flutter widget update pattern is a little bit confusing when coming from "old/classic" win32.
For instance :
I have a widget "button" => I click on it => I update a cell in a widget "datatable".
With classic API (VCL, Net Forms, ...) I get the address of button (by name, id, ...) and call directly
datatable_address.cell[x,y] = new_value;
I understand that I have to use setState() but do I need to create an "event" in Datatable (to run its setState()) and fire up this event from my button ?
(BloC seems pretty close to Qt signals)
The difference is composition vs aggregation. The widgets themselves are immutable so you can't change the value inside a widget.
What you can do is create a new object with latest values. Flutter framework will take care of the rest. For example,
when you do setState in parent widget of both button as well as datatable, you build method of said widget is called. Now, you will create a new datatable object with updated cell values. Internally, flutter will handle this.
You can only do setState in State class which is not immutable which is linked to Stateful widget which themselves are immutable.
This architecture comes with its own set of problems like if you need to update some UI based on some button press, you will have to have the logic inside the common widget of both the affected widget and button. That's where Stream/Bloc comes into picture.
So I have a call a timer function on pressing the login button in the main file. The timer function is defined in the login verification file. So how can I call the timer function in main file so that when the login button is pressed and when it goes to the login verification the timer starts?
If you want to use some parent's function in child widget then it is easy - just pass the reference to the function you want through the constructor.
If you want to use some child's function in parent widget then the situation is a little bit different - you have to pass a GlobalKey to identify the state of child widget when creating an instance of this widget. You can refer to this https://stacksecrets.com/flutter/how-to-call-method-of-a-child-widget-from-parent-in-flutter.
If you want to use a function from a widget that is not either a child or parent widget, then you might think of using some state managment solution (such as Provider or GetX or Bloc) to provide it to all the widget that needs some information from it.
Can we pass the stateful widget created in one dart file to another dart file along with the setState changes and render that widget as the body in another stateful dart file.
Actually i am able to get the body but my setState is not working.
i want to pass the stateful widget(ie widget with dropdownbutton) to another page and my setState should work and i should be able to capture the data.
When you want to call the parent method, you can use state up. (Give call back to parent).
and if you want to call child method from a parent you can use GlobalKey.