private fun sendListOfFeedBack(listOfFeedBack: ArrayList<FeedbackModel>, email: String,
                                   firstName: String,
                                   lastName: String,
                                   uuid: String): Single<String?> {
        if (checkNetworkDataAvailableOrNot()) {
            for (i in 0 until listOfFeedBack.size) {
                // ToDo We have to apply Logic to execute synchronus
                uploadImageAndToFireBase(listOfFeedBack[i],email, firstName, lastName, uuid)
            }
            appPreference.clearAllFeedback()
            return Single.just(REMOTE_SAVED)
        }
        return Single.just(LOCAL_SAVED)
    }

  private fun uploadImageAndToFireBase( feedbackModel: FeedbackModel, email: String, firstName: String, lastName: String, uuid: String ) {
        val listOfImagePath = java.util.ArrayList<String>()
        if (feedbackModel.imageList.size > 0) {
            for (i in 0 until feedbackModel.imageList.size) {
                val ref = storageReference?.child("tests/feedback/images$i.jpg")
                val uploadTask = ref?.putFile(Uri.parse(feedbackModel.imageList[i]))
                val urlTask = uploadTask?.continueWithTask { task ->
                    if (!task.isSuccessful) {
                        task.exception?.let {
                            throw it
                        }
                    }
                    ref.downloadUrl
                }?.addOnCompleteListener { task ->
                    if (task.isSuccessful) {
                        val downloadUri = task.result
                        Log.d("STATUSSS", "Uploaded$downloadUri")
                        listOfImagePath.add(downloadUri.toString())
                        if (feedbackModel.imageList.size == listOfImagePath.size) {
                            uploadDataToFirebaseFeedbackDocument( feedbackModel, listOfImagePath, email, firstName, lastName, uuid )
                        }
                    } else {
                        uploadDataToFirebaseFeedbackDocument( feedbackModel, listOfImagePath, email, firstName, lastName, uuid )
                    }
                }
            }
        } else {
            uploadDataToFirebaseFeedbackDocument( feedbackModel, listOfImagePath, email, firstName, lastName, uuid )
        }
    }

这是我的代码，我试图在循环中上传更多的图像，然后我们将imageUrl发送到firestore数据库，在这种情况下，有时listofimagepath变空，因为在图像上传数据发送到firestore之前，我试图先上传图像，然后我想发送数据，即我想执行同步循环，请帮助我如何同步上传数据到firestore，我正在使用rxkotlin。