What difference between stateless and stateful widgets?

Question

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?

Answer 1

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.

Answer 2

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.

Answer 3

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.