How to know if list view is scrollable programatically - flutter

Question

I am copying my question from here as it is the same question but for flutter
How do you know if your ListView has enough number of items so that it
can scroll?
For instance, If I have 5 items on my ListView all of it will be
displayed on a single screen. But if I have 7 or more, my ListView
begins to scroll. How do I know if my List can scroll
programmatically?
Thank you
I am adding the code I tried, in which I test if the controller is attached, to be able to get the position. I couldn't get the position because the controller is not attached until you actually scroll
Widget build(BuildContext context) {
_afterBuild();
ListView.builder(
controller: controller,
// ...
)
}
Future<void> _afterBuild () async {
if (controller.hasClients) {
print("controller.hasClients");
// here I would be able to get the position
} else {
print("controller.has no Clients");
}
}
Edit: For anyone coming here: The controller was not being attached because I had a condition under which to build the ListView
So I combined the comments with the accepted answer (which is actually the answer for the question) and solved it like this (with some pseudocode):
Widget build(BuildContext context) {
if (not loaded results from api) {
return Something()
} else {
Future(_afterBuild);
return ListView.builder(
controller: controller,
// ...
)
}
}
Future<void> _afterBuild () async {
if (controller.hasClients) {
if(controller.position.maxScrollExtent > 0){
print('it can be scrolled');
}
} else {
print("controller has no client");
}
}

Answer 1

Actually it's quite easy to do in Flutter. You should have a ScrollController attached to your ListView and then you can check the maxScrollExtent. If it's bigger than zero then your ListView can be scrolled. It also works for any scrolling view which uses ScrollController.
#override
void initState() {
super.initState();
WidgetsBinding.instance.addPostFrameCallback((timeStamp) {
if(controller.position.maxScrollExtent > 0){
print('it can be scrolled');
}
});
}

Answer 2

Step 1 - Assign a GlobalKey
GlobalKey myKey= GlobalKey();
Step 2 - Assign key to ListView
ListView(
key: myKey,
...
)
Step 3 - In your function that checks if the ListView is scrollable, use the following code-
final RenderBox renderBoxRed = myKey.currentContext.findRenderObject();
final height = renderBoxRed.size.height; // find height of ListView
if (height > MediaQuery.of(context).size.height) { // checking if listview height is greater than page height
print("ListView is SCROLLABLE !!!");
}

Answer 3

I like where most of the rest of the answers are going, but they aren't getting the data the most succinctly or reliably. What you want to do is, yes, attach a ScrollController, and then look for the .position on that (which may throw if there's no single attached position). Then, ask the position for extentAfter and extentBefore, and you'll discover how much virtual view (in pixels) there is after and before the current visible portion. If those are 0, no scrolling. No need to figure out the size of the screen or the containers. Flutter already knows all that when it laid everything out!