What I want to do : When the user want to change their name on app, User going to modify : when the user showing this screen, already enter his name in this textfiled. He can change it.

Example: In the picture, the user going to modify his username His firebase username is "default". It's already typed. he remove "t" and submit.

My code here

 class ModifyScreen extends StatefulWidget {
      final String uid;
      const ModifyScreen({
        super.key,
        required this.uid,
      });
    
      @override
      State<ModifyScreen> createState() => _ModifyScreenState();
    }
    
    class _ModifyScreenState extends State<ModifyScreen> {
      var userData = {};
      bool isLoading = false;
    
      @override
      void initState() {
        getData();
        super.initState();
      }
    
      getData() async {
        
        try {
          var userSnap = await FirebaseFirestore.instance
              .collection('users')
              .doc(widget.uid)
              .get();
    
          userData = userSnap.data()!;
          setState(() {});
        } catch (e) {
          showSnackBar(
            context,
            e.toString(),
          );
        }
        
      }
    
      @override
      Widget build(BuildContext context) {
        TextEditingController _namecon = TextEditingController();
        return Scaffold(
                body: Padding(
                  padding: const EdgeInsets.all(18),
                  child: Center(
                    child: Column(
                      mainAxisAlignment: MainAxisAlignment.center,
                      children: [
                        TextField(
                          controller: _namecon,
                          decoration:
                              InputDecoration(hintText: userData['username']),
                        )
                      ],
                    ),
                  ),
                ),
              );
      }
    }

CodePudding user response：

Remove decoration and add _namecon.text = userData['username'] in build, also take TextEditingController _namecon = TextEditingController() outside of build