Callback function not working in flutter

Question

Creating an example to learn callbacks in Flutter. It's a simple programme to increase the counter onTap of a GestureDetetor But, the callback method is not working. The count increase on hot reload but not on tap. Below is the code with comments.

class BoxState extends State<ChangeBoxState>{
  int _counter = 0;

  //Callback method changes the state onTap of GestureDetector widget. It is not calling onTap.
  increaseCount(){
    setState(() {
      ++_counter;
      print(_counter);
    });
  }

  @override
  Widget build(BuildContext context) {
    // Passing the callback method,"increaseCount()" to stateless class where GestureDetector is defined.
    return BoxWidget(onPressed: increaseCount(), counter: _counter,);
  }

}

Stateless class:

class BoxWidget extends StatelessWidget{

  BoxWidget({this.onPressed, this.counter});

  final VoidCallback onPressed;
  final int counter;

  @override
  Widget build(BuildContext context) {
    // TODO: implement build
    return Container(
      decoration: BoxDecoration(color: Colors.blue[500]),
      child: Column(
        children: <Widget>[Center(child: Text('Hello, world!')),
        GestureDetector(
          onTap: onPressed, //Passing onPressed to onTap.

          child: Container(
            margin: const EdgeInsets.only(left:0.0, top:200.0, right:0.0, bottom:0.0),
            height: 200.0,
            width: 200.0,
            decoration: BoxDecoration(
              color: Colors.teal[200],
              border: Border.all(color: Colors.yellow, width: 10.0, style: BorderStyle.solid),
              borderRadius: BorderRadius.all(Radius.circular(20.0)),
            ),
            child: Center(child: Text(counter.toString())),
          ),
        ),
        ],
      ),
    );
  }
}

Answer 1

remove the the bracket in increaseCount() because using the bracket you are creating an instance of your VoidCallback and this will run one time only so try this

return BoxWidget(onPressed: increaseCount, counter: _counter,);

Answer 2

You should provide the reference of increaseCount to the onPressed callback.

Here you are assigning increaseCount() (check braces) to the callback which first call increaseCount() function and its return value will be assigned to the onPressed. Thats why it is only incrementing one time on hot reload.

return BoxWidget(onPressed: increaseCount, counter: _counter,);