Is it possible to make a Text Widget Stateful so that the Text can be changed when i press a Button without having my Class to be Stateful?
example:
class Rangliste extends StatelessWidget{.... Text(Test), Text(Test2)....}
Test and Test2 are Strings.
So when i press a Button the values inside the Text Widgets should change. Is there any Way to achieve this without changing my Class to Stateful? Or if not can somebody explain how i can change the Class to Stateful without messing up the rest of my Code
No, you can't, a stateless widget is an immutable widget that cannot react to state changes and rerender, you will have to use some form of state management.
If your button and your text and your data are all within the same widget, then it is better to make your widget Stateful and use setState(() {}) to change your text and rerender.
You can use the Flutter plugin in order to convert your widget from a Stateless widget to a StatefulWidget, the plugin will handle everything.
Related
In the Flutter job interviews, sometimes I am asked how we can rebuild the StatelessWidget and the answer to this is to call the markNeedsBuild() method of the widget's Element or BuildContext.
So the question is, are there any cases when we need to rebuild a StatelessWidget and it's better to use a StatelessWidget instead of the StatefulWidget?
I found cases where people wanted to rebuild the StatelessWidget, such as How to invoke a rebuild of a stateless widget?, but in all these cases it was better to use StatefulWidget or state management instead.
The whole purpose of the StatelessWidget is not to rebuild.
If you require rebuild you have to use StatefullWidget.
I guess the interviewers are trying to trick you xD
Summary
Stateless Widget:
Stateless Widgets are static widgets.
They do not depend on any data change or any behavior change.
Stateless Widgets do not have a state, they will be rendered once and will not update themselves, but will only be updated when external data changes.
For Example: Text, Icon, RaisedButton are Stateless Widgets.
Stateful Widget:
Stateful Widgets are dynamic widgets.
They can be updated during runtime based on user action or data change.
Stateful Widgets have an internal state and can re-render if the input data changes or if Widget’s state changes.
For Example: Checkbox, Radio Button, Slider are Stateful Widgets
I'm using Stateless Widget that doesn't need anything to be change in that class while running but i'm using a formkey in this class so is it necessary to convert this class to stateful widget or it is ok to leave it with Stateless Widget.
Note: I'm not using TextEditing controllers in this Widget while i'm using the onSaved method.
I'm quite new to flutter and I'm trying to figure out the best way to build my widgets in the aspect of good performance while I have three choices:
1- Stateful Wigdet.
2- Stateless Widget.
3- Widget function(){} with a StatefulBuilder if needed.
Thanks.
A StatefulWidget has State, which means that you can change stuff inside the widget without needing to destroy it and create a new version. They work slower than StatelessWidget but are better for checkboxes or screens which need to be frequently updated.
A StatelessWidget is locked, and you cannot change values once it is initiated. In order to change things inside the widget, you need to re-call the build function to build an updated version. They are quite fast but are best used for static screens.
Widget function(){} widgets are custom-made. Essentially, you can take any existing widget and modify it, adding childs and other widgets to it. However, the widget type normally inherits from a StatefulWidget or StatelessWidget. These can cover basically everything.
The core concept of StatelessWidget and StatefulWidget is confusing to me.
According to flutter documentary:
A widget is either stateful or stateless.
If a widget can change—when a user interacts with it, for example—it’s stateful.
A stateless widget never changes. Icon, IconButton, and Text are examples of stateless widgets. Stateless widgets subclass StatelessWidget.
so mainly if you have something on the screen that changes when user interacts with it, you should use stateful widget for it and otherwise, you should use stateless widget.
for example if you have a plus button on the screen and a a number on the screen which should be increased every time the user press it, you should use stateful widget to notify flutter that the text on the screen should be changed and rerendered.
for more information you can check here.
I am learning Dart/flutter and trying to understand how Widgets system works. But I can't understand what difference between stateless and stateful widgets? For example I have button. What type it have?
Let's imagine two cases.
I send text to button and it's display it.
I send text to button and it's change color.
What will be if I will create not proper Widget type?
There are 3 kind of widgets, not just 2.
Stateful widget
Stateless widget
Inherited widget
A stateless widget is like a constant. It is immutable. If you want to change what is displayed by a stateless widget, you'll have to create a new one.
Stateful widgets are the opposite. They are alive and can interact with the user. Stateful widgets have access to a method named setState, which basically says to the framework "Hello, I want to display something else. Can you redraw me please ?".
Finally, Inherited widget is a mixt of both worlds. It is immutable and stateless. But another widget (whatever it is) can subscribe to that inherited widget.
Which means that when you replace your inherited widget by a new one, all the widgets that has subscribed to the old one will be redrawn.
In the end, a stateful widget will usually be used like a Controller.
A stateless widget will be used like a View.
And the inherited widget will be your configuration file or your Model.
According to flutter.io:
Stateless widget
Stateless widgets are immutable, meaning that their properties can’t
change — all values are final.
Here is doc.
Stateful widget
Stateful widgets maintain state that might change during the lifetime
of the widget. Implementing a stateful widget requires at least two
classes: 1) a StatefulWidget class that creates an instance of 2) a
State class. The StatefulWidget class is, itself, immutable, but the
State class persists over the lifetime of the widget.
As a example if you want to change text in text widget when a button press, you have to use StatefulWidget and it will let you to change the state of a variable.
But in StatelessWidget you cannot do that because it doesn't keep state.
Read more from doc.
This tutorial will help anyone who trying to understand these two.
Check out the Flutter Interactivity Tutorial.
If your widget's build method depends entirely on its immutable constructor arguments, you should use a StatelessWidget because they're simpler. If you want to store some persistent private data that you expect to mutate over time, use a StatefulWidget and store the data on the State.