initState and dispose

Learn the initState and dispose lifecycle methods.

Lifecycle

A State object has a lifecycle. initState is called once when the State is first inserted into the tree; here you set up database connections, listeners or controllers (denetleyici). dispose is called when the State is removed from the tree; here you clean up the resources you created.

class _SayacState extends State<Sayac> {
  late TextEditingController denetleyici;

  @override
  void initState() {
    super.initState();
    denetleyici = TextEditingController();
  }

  @override
  void dispose() {
    denetleyici.dispose();
    super.dispose();
  }
}

Resource cleanup

Every resource opened in initState must be closed in dispose. Otherwise a memory leak occurs. Objects such as TextEditingController, StreamSubscription and AnimationController are closed in the dispose method. super.dispose() must always be called.

@override
void dispose() {
  denetleyici.dispose();      // release the controller
  dinleyici.cancel();         // cancel the subscription
  super.dispose();            // notify the superclass
}

Exercise Print lifecycle info

In main, print two lines with print: initState baslar and dispose bitir.

Show example solution

void main() {
  print('initState baslar');
  print('dispose bitir');
}

Test yourself

When is initState called?
- Every time setState is called
- Once when the State is first inserted into the tree
- Repeatedly every time the app opens
- Before every build
Show answer

Once when the State is first inserted into the tree — initState is called once when the State is first inserted; resource setup is done here.

Lifecycle method

@override
void ____() {
  super.dispose();
  denetleyici.dispose();
}

Show answer

@override
void dispose() {
  super.dispose();
  denetleyici.dispose();
}

Lifecycle concepts

initState

Called once when State is inserted
dispose

Called when State is removed
lifecycle

State's start-to-end lifetime
memory leak

Happens when a resource is not closed

Next lesson: Summary - StatefulWidget

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