In a line, if your widget change appearance use stateful widget and if it doesn't use stateless widget that's all. We know that flutter is all about widgets and in flutter there are 2 types of widgets.
A stateless widget never changes. For example Icon, IconButton, Text and so on. Once they are built they remain the same during the lifetime of the application. There are various places where you might want to use Stateless widget such as your app Title, Images, and so on.
A stateful widget is something which has a state so basically that widget needs to be rebuilt whenever some event occurs. A good example would be a toggle button. Whenever you tap on the toggle button its state changes to either on or off. The appearance of the button changes and this happens because the stateful widget asks the build method to rebuild the widget and change its state.
Sample Stateless Widget Code:
Sample Stateful Widget Code:
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