private async void Button_Click_2(object sender, RoutedEventArgs e)
        {
            var fop = new FileOpenPicker();

            fop.FileTypeFilter.Add(".yfpwd");
            var file = await fop.PickSingleFileAsync();

            if (file != null)
            {
                await file.CopyAndReplaceAsync(await TmpData.GetPwdFileAsync());

                Frame.Navigate(typeof(PasswordInputPage));
            }
        }
        private async void Button_Click(object sender, RoutedEventArgs e)
        {
            savebtn.IsEnabled = false;
            try
            {
                var fsp = new FileSavePicker
                {
                    DefaultFileExtension = ".yfpwd"
                };
                fsp.FileTypeChoices.Add("yfpwd", new List <string> {
                    ".yfpwd"
                });
                var file = await fsp.PickSaveFileAsync();

                if (file != null)
                {
                    await(await TmpData.GetPwdFileAsync()).CopyAndReplaceAsync(file);
                }
            }
            finally
            {
                savebtn.IsEnabled = true;
            }
        }