private async void fileOpenButton_Click(object sender, RoutedEventArgs e)
        {
            var picker = new Windows.Storage.Pickers.FileOpenPicker();

            picker.ViewMode = Windows.Storage.Pickers.PickerViewMode.Thumbnail;
            picker.SuggestedStartLocation = Windows.Storage.Pickers.PickerLocationId.Desktop;
            picker.FileTypeFilter.Add(".txt");

            var files = await picker.PickMultipleFilesAsync();

            {
                foreach (StorageFile i in files)
                {
                    UploadedFile nf = new UploadedFile(i);
                    await nf.GetFileSz();

                    uploadedFileLists.Add(nf);
                }
            }
        }
        private async void Canvas_Drop(object sender, DragEventArgs e)
        {
            if (e.DataView.Contains(StandardDataFormats.StorageItems))
            {
                var items = await e.DataView.GetStorageItemsAsync();

                if (items.Any())
                {
                    foreach (var item in items)
                    {
                        var storageFile = item as StorageFile;
                        var FileType    = storageFile.FileType;

                        if (FileType == ".txt")
                        {
                            UploadedFile nf = new UploadedFile(storageFile);
                            await nf.GetFileSz();

                            uploadedFileLists.Add(nf);
                        }
                    }
                }
            }
        }