Firebase 返回 null photoUrl

Question

I am building a mock social media app that allows users upload profile pictures to create their profiles. I am building this app in flutter. Right now, here's my uploadPic method:

Future uploadPic(BuildContext context) async{

    String fileName = basename(_image.path);
    FirebaseStorage storage = FirebaseStorage.instance;
    var photoUrl;

    Reference ref = storage.ref().child(fileName);
    var storedImage = File(_image.path);
    UploadTask uploadTask = ref.putFile(storedImage);
    uploadTask.then((res) {
      photoUrl = res.ref.getDownloadURL();
    });


    print("photo url -- $photoUrl");
    await widget.user?.updatePhotoURL(photoUrl);
    await FirebaseAuth.instance.currentUser?.updatePhotoURL(photoUrl);
  }

I have added the right permissions in my firebase console to allow read and write to the database. I know this because when I check firebase storage, I see the pictures have been uploaded successfully. However, when I try to print the returned photo url (after the upload task completes), I get a null value. This is a problem when I try to access the photo in other areas in the app, because the user photoUrl in firebase is null.

Is there anything I am doing wrong concerning the upload of the pic to firebase? Also, my terminal returns this: No App Check token for request. . I'm wondering if this has anything to do with the issue?

Any help would be greatly appreciated!

Answer 1

your problem is simple, it's exactly from here:

var photoUrl;
uploadTask.then((res) {
   photoUrl = res.ref.getDownloadURL();
});
print(photoUrl); // null

the problem is you are trying to print photoUrl variable without waiting for the future uploadTask to finish its work which results null .

the solution is to wait for uploadTask future before printing the photoUrl variable:

var photoUrl;
await uploadTask.then((res) async {
   photoUrl = await res.ref.getDownloadURL();
});
print(photoUrl);

the solution on your code:

Future uploadPic(BuildContext context) async{

    String fileName = basename(_image.path);
    FirebaseStorage storage = FirebaseStorage.instance;
    var photoUrl;

    Reference ref = storage.ref().child(fileName);
    var storedImage = File(_image.path);
    UploadTask uploadTask = ref.putFile(storedImage);
    await uploadTask.then((res) async {
       photoUrl = await res.ref.getDownloadURL();
    });


    print("photo url -- $photoUrl");
    await widget.user?.updatePhotoURL(photoUrl);
    await FirebaseAuth.instance.currentUser?.updatePhotoURL(photoUrl);
  }