if (!title.isEmpty() &&  !contact.isEmpty() && !cities.isEmpty() && pickedImageUri!=null
            && !author.isEmpty() && !publisher.isEmpty()){
                StorageReference storageReference= FirebaseStorage.getInstance().getReference().child("BOOK_COVERS_PDF'S");
                final StorageReference imageFilePath=storageReference.child(imageAndPdfUri(pickedImageUri,pdfUri).getLastPathSegment());

                imageFilePath.putFile(imageAndPdfUri(pickedImageUri,pdfUri)).addOnSuccessListener(new OnSuccessListener<UploadTask.TaskSnapshot>() {
                    @Override
                    public void onSuccess(UploadTask.TaskSnapshot taskSnapshot) {
                        imageFilePath.getDownloadUrl().addOnSuccessListener(new OnSuccessListener<Uri>() {
                            @Override
                            public void onSuccess(Uri uri) {
                                String imageDownloadLink=uri.toString();
                                ExtendedPost extendedPost=new ExtendedPost(title,author,categorySpinner,
                                        editionSpinner,publisher,contact,cities,imageDownloadLink,
                                        currentUser.getUid(),currentUser.getDisplayName(),currentUser.getPhotoUrl().toString(),imageDownloadLink);


                                //add post to firebase
                                addPost(extendedPost);

                            }
                        });

                    }
                }).addOnFailureListener(new OnFailureListener() {
                    @Override
                    public void onFailure(@NonNull Exception e) {
                        showMessage(e.getMessage());
                        progressBar.setVisibility(View.INVISIBLE);
                        btnPost.setVisibility(View.VISIBLE);

                    }
                });
private Uri imageAndPdfUri(Uri image,Uri pdf){
    this.pickedImageUri=image;
    this.pdfUri=pdf;
    boolean trueStatePickImage=true;
    boolean trueStatePicPdf=true;

        if (trueStatePickImage){
            this.pickedImageUri=image;
            return image;
        }
        if (trueStatePicPdf){
            this.pdfUri=pdf;
            return pdf;

        }

    return null;

}