FLUTTER: returned value is NULL-CodePudding

I am working on an Exercises app. I am using FIREBASE with a StreamBuilder to retrieve an "exercise id" that has been favorited in my app. This is working fine and I get the correct Id. I then pass it to a simple method to retrieve the actual "exercise" so that I can display it. This method passes through a List of exercises, checking if the exercise id, is found, and then I want it to return the exercise. However I am always getting null returned. I can't figure out why this is.

I'd really appreciate some help, as very stuck with it right now.

Here below is my code:

This is the method:

Exercise getExerciseByID(String exerciseId) {
  _exercises.forEach((exercise) {
    print('COMPARE1: ${exercise.id} AND $exerciseId');
    if (exercise.id == exerciseId) {
      print('COMPARE2: ${exercise.id} AND ${exerciseId}');
      return exercise;
    }
  });
}

Note that the two print statements both print and show matching id's

And here is the Build with StreamBuilder etc..

    return Scaffold(
  body: StreamBuilder(
    stream: FirebaseFirestore.instance
        .collection('favorites')
        .doc('${_firebaseAuth.currentUser.uid}')
        .collection('userFavorites')
        .snapshots(),
    builder: (BuildContext context, AsyncSnapshot<QuerySnapshot> snapshot) {
      if (!snapshot.hasData)
        return Center(
          child: CircularProgressIndicator(),
        );
      return ListView.builder(
        itemCount: snapshot.data.docs.length,
        itemBuilder: (context, index) {
          //TODO: GET EXERCISE FOR DOC
          String _exerciseId = snapshot.data.docs[index].id;
          _exercise = getExerciseByID(_exerciseId);
          //TODO: DISPLAY CARD
          print("Retrieved Exercise: $_exercise");
          return Center(child: Text(""));
        },
      );
    },
    //   padding: EdgeInsets.only(left: sideMargin),
    // },
  ),
);

Note: the print statement: print("Retrieved Exercise: $_exercise"); is where I am always finding the NULL.

Many thanks for any assistance.

CodePudding user response：

change this

Exercise getExerciseByID(String exerciseId) {
  _exercises.forEach((exercise) {
    print('COMPARE1: ${exercise.id} AND $exerciseId');
    if (exercise.id == exerciseId) {
      print('COMPARE2: ${exercise.id} AND ${exerciseId}');
      return exercise;
    }
  });
}

to this

Exercise getExerciseByID(String exerciseId) {
Exercise returningExercise;
  _exercises.forEach((exercise) {
    print('COMPARE1: ${exercise.id} AND $exerciseId');
    if (exercise.id == exerciseId) {
      print('COMPARE2: ${exercise.id} AND ${exerciseId}');
      returningExercise = exercise;
    }
  });
return returningExercise;
}

You are returning inside ForEach Statement. This doesn't return to your function. put return statement outside ForEach statement.
Note: This solution is not best. But you now know whats going wrong.