Flutter ScrollController NoSuchMethodError: invalid member on null: 'addListener'

i've been trying to make a listview in flutter and get how many pixels the view had scrolled. Unfortunately, i used NotificationListener

Like this:

          NotificationListener<ScrollUpdateNotification>(
              child: ListView(
                children: [
                    //content here
                ],
              ),
              onNotification: (notification) {
                //How many pixels scrolled from pervious frame
                // print("scrollDelta: ${notification.scrollDelta}");
                setState(() {
                  this.scrollValue = notification.metrics.pixels;
                });
                //List scroll position
                // print("metrics.pixels: ${notification.metrics.pixels}");
                return true;
              },
            ),

Issue is that it gave some very poor performance with my application.

So i noticed that you could use a controller directly with the ListView and i made the following code:

ScrollController controller;
    controller.addListener(() {
      print("i'm here");
    });

    var scaffold = Scaffold(
        backgroundColor: Color(0xFFFFFFFF),
        resizeToAvoidBottomPadding: false,
        body: Stack(
          children: [
            ListView(
              controller: controller,
              children: [
                  //content here
              ],
            ),
          ],
        ),
     );

But then i get the following error :

NoSuchMethodError: invalid member on null: 'addListener'

I currently have no idea how to get how many pixel were scrolled in a listview without hindering greatly the performances.

Your ScrollController is initialized as null.

Just give it a value:

ScrollController controller = ScrollController();

Make sure you dispose of it using the dispose method of your StatefulWidget.

@override
void dispose(){
   controller.dispose();
}