Flutter how to execute when clicking back button

15
votes

I have a page that is called from bottom tab nav which executes a initState function, I then navigate to a page via button click that has details and actions to take, however when I click the back button to goto originating page, the initState does not run again, I have found out that because Flutter does not destroy the page when you put one on top, since the NAV is not on new page as its not in the menu, how do I make initState run again on clicking back button or is there another way to listen for that navigate from back button and run the code that needs to update data?

Any help would be great.

2
flutterdartnavigationback-button
You do not want to call initState again, it is easier to just change the state depending on Navigator.pop – Shady Aziza
How do I do that, this is the back button in the appBar, is there a way to affect that with a pop? – Robert
Check my answer down below – Shady Aziza
@Robert see this link, i have answered this question on how to call initState or update data when back button on navigation bar was pressed stackoverflow.com/questions/51927885/… – ArgaPK

2 Answers

21
votes

You can override the default back arrow on the AppBarand then specify the value you would like to return to trigger the change of the state when Navigator.pop is called:

Pseudo-Code

so you need to have something like this in your onPressed callback of your navigation button

onPressed: ()async{
            var nav = await Navigator.of(context).push(newRoute);
            if(nav==true||nav==null){
              //change the state
            }
          },

and in your newRoute you should have something like this

new AppBar(
        leading: new IconButton(
          icon: new Icon(Icons.arrow_back),
          onPressed: (){Navigator.pop(context,true)}
        ),

I am checking for both values null or true because the null value is returned when the user hits the BackButton on android screen (the one in the bottom of the screen). I also believe the null will also be returned with the default BackButton in Flutter so you do not actually need to override the leading property, but I have not checked that myself, so it may be worth checking.

26
votes

You can listen to the pop with WillPopScope (Creates a widget that registers a callback to veto attempts by the user to dismiss the enclosing [ModalRoute]. -> from documentation):

@override
Widget build(BuildContext context) {
 return WillPopScope(
  onWillPop: () {
    print('Backbutton pressed (device or appbar button), do whatever you want.');

    //trigger leaving and use own data
    Navigator.pop(context, false);

    //we need to return a future
    return Future.value(false);
  },
  child: Scaffold(
  ...
  ),
 );
}

Hopefully I got your question right and that helps :)!