Erro when using File Transfer Plugin - Ionic 3 - ionic-framework

Question

I am trying to upload images to my server using
"cordova-plugin-file-transfer": "^1.7.1",
"#ionic-native/file-transfer": "^5.0.0",
component.ts
takePicture() {
const options: CameraOptions = {
quality: 50,
destinationType: this.camera.DestinationType.FILE_URI,
encodingType: this.camera.EncodingType.JPEG,
mediaType: this.camera.MediaType.PICTURE,
sourceType: this.camera.PictureSourceType.PHOTOLIBRARY,
targetWidth: 500,
targetHeight: 500,
saveToPhotoAlbum: false
};
this.camera.getPicture(options)
.then((imageData) => this._img.uploadImage(imageData))
.catch(err => console.log(err));
}
imageProvider.ts
import { FileTransfer, FileUploadOptions, FileTransferObject } from "#ionic-native/file-transfer/ngx";
...
uploadImage(img) {
const url = `${this.apiURL}/images/upload`;
// File for Upload
var targetPath = img;
var options: FileUploadOptions = {
fileKey: 'image',
chunkedMode: false,
mimeType: 'multipart/form-data'
};
const fileTransfer: FileTransferObject = this.transfer.create();
fileTransfer.upload(targetPath, url, options)
.then(() => {
console.log('good');
}, (err) => {
console.log('bad');
})
}
I get this error in logcat Android Studio:
"TypeError: Cannot read property 'constructor' of undefined"
I have found that the code works well till it reaches this line
const fileTransfer: FileTransferObject = this.transfer.create();

Answer 1

You are using the wrong native plugin version, For Ionic 3, you should use version 4.
ionic cordova plugin add cordova-plugin-file-transfer
npm install --save #ionic-native/file-transfer#4
And also, don't append ngx at the end of the import.
import { FileTransfer, FileUploadOptions, FileTransferObject } from '#ionic-native/file-transfer';
For your future reference, If you are using Ionic 3, follow Ionic v3 docs instead of latest docs.
V3 docs: https://ionicframework.com/docs/v3/native/file-transfer/

Answer 2

you might be missing this line after the imports:
constructor(private transfer: FileTransfer, private file: File) { }
that's at least what the documentation suggests.