Text not changing even by using setState-CodePudding

String title = '';
child: GestureDetector(
                      onTap: () {
                        setState(
                          () {
                            final docRef = FirebaseFirestore.instance
                                .collection('CIPsubmit')
                                .doc(wee)
                                .get()
                                .then(
                              (DocumentSnapshot doc) {
                                final data = doc.data() as Map<String, dynamic>;
                                final title = data['title'];
                                print(title.toString());
                              },
                            );
                          },
                        );
                      },

I am getting a string from firebase, and have put it in a setState to change a text value. The print shows that String title has updated to the right value, but the text is not changing.

CodePudding user response：

It is not a good idea to put an asynchronous function, because the time when setState update the widget tree is NOT when the string is updated. The fix is also simple:

                        onTap: ()  async /* NOTE: mark the anonymous function as asynchronous */ {
                            final docRef = await FirebaseFirestore.instance
                                .collection('CIPsubmit')
                                .doc(wee)
                                .get();
                            final data = docRef.data() as Map<String, dynamic>;
                            final title = data['title'];
                            setState(() { print(title.toString();})
                            print(title.toString());
                              },
                            );
                          },
                        );

CodePudding user response：

First of all, title variable above GestureDetector is not the same with title inside that code

(DocumentSnapshot doc) {
     final data = doc.data() as Map<String, dynamic>;
     final title = data['title'];//with this. Instead you need to write below line code
     // title = data['title'];
     print(title.toString());
     },

Secondly, it seems very bad wrapping whole code in onTap with setState. You need to just wrap line, which you change title variable value.

setState((){
    title = data['title'];
});

And finally, a title variable(it is preferred declare all variables in State class out of build method) should be declared out of build method.