getDownloadUrl（）返回的值不正确

Question

此处提供的解决方案（How to get URL from Firebase Storage getDownloadURL）是指已弃用的方法。

我尝试了此处提供的其他解决方案，但没有成功。从Android Studio 3.2.1开发的Android应用程序将图像上传到Firebase后，我无法检索正确的下载URL。在Android Studio中运行调试器时，我可以在downloadUrl变量中看到正确的结果，但无法弄清楚如何访问它。如何访问下面的屏幕快照中的zzaa给出的值并将其存储在变量downloadUrl中？

下面是调试器的屏幕快照，所需的值在zzaa上可见。

这是我的代码：

    Uri selectedImageUri = data.getData();
    //Get a reference to store file at chat_photos/<FILENAME>
    StorageReference photoRef = 
    mChatPhotosStorageReference
        .child(selectedImageUri.getLastPathSegment());
    UploadTask uploadTask = photoRef.putFile(selectedImageUri);
    // Upload file to Firebase Storage
    uploadTask
        .addOnSuccessListener(this, new OnSuccessListener<UploadTask.TaskSnapshot>() {
        public void onSuccess(UploadTask.TaskSnapshot taskSnapshot) {
            // When the image has successfully uploaded, we get its download URL
            Task<Uri> downloadUrl = 
                taskSnapshot
                    .getMetadata()
                    .getReference()
                    .getDownloadUrl();
            // Set the download URL to the message box, so that the user can send it to the database
            FriendlyMessage friendlyMessage = new FriendlyMessage(null, mUsername, downloadUrl.toString());
            mMessagesDatabaseReference.push().setValue(friendlyMessage);