flutter : This expression has a type of 'void' so its value can't be used.

I am recording data coming from the user. I do need to get the document ID as soon as the document has been created. I have done some research and find this. But I am getting this error. Please, can you help me to fix this? Thank you.

 CollectionReference users = FirebaseFirestore.instance
        .collection('Users')
        .doc(FirebaseAuth.instance.currentUser!.uid)
        .collection('allTasks');


    DocumentReference doc = await users
        .add({
      'task_Name' : _valueTaskNameSaved,
      'project_Name': selectedProjectCapture,})
      .then((value) => print("Task Created"))
      .catchError((error) => print("Failed to add task: $error"));

CodePudding user response：

There is syntax error in your code.

Change from

 DocumentReference doc = await users
        .add({
      'task_Name' : _valueTaskNameSaved,
      'project_Name': selectedProjectCapture,)}

To this

 DocumentReference doc = await users
                      .add({
                  'task_Name' : _valueTaskNameSaved,
                  'project_Name': selectedProjectCapture,})

CodePudding user response：

CollectionReference#add(T data) function returns an object of type Future<DocumentReference<T>>. So there is no way you can save such an object into a variable of type DocumentReference. Actually, there is no need to save that at all. So to solve this, you can simply use:

users.add({
         'task_Name' : _valueTaskNameSaved,
         'project_Name': selectedProjectCapture})
    .then((_) => print('Document added'))
    .catchError((error) => print('Failed with: $error'));

CodePudding user response：

In fact, to make it work I have remove the end of the code. I have added // to the lines to remove. Now the error has disapeared

CollectionReference users = FirebaseFirestore.instance
        .collection('Users')
        .doc(FirebaseAuth.instance.currentUser!.uid)
        .collection('allTasks');


    DocumentReference doc = await users
        .add({
      'task_Name' : _valueTaskNameSaved,
      'project_Name': selectedProjectCapture,})
    //  .then((value) => print("Task Created"))
    //  .catchError((error) => print("Failed to add task: $error"));