Downloading file to a custom folder in wpf c#

downloadfile.cs

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Net;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace Download
{
	/// <summary>
	/// Interaction logic for MainWindow.xaml
	/// </summary>
	public partial class MainWindow : Window
	{
		public MainWindow()
		{
			InitializeComponent();
	
		}

		private void Button_Click(object sender, RoutedEventArgs e)
		{
			Microsoft.Win32.SaveFileDialog dlg = new Microsoft.Win32.SaveFileDialog();
			dlg.FileName = "myimage"; // Default file name
			dlg.DefaultExt = ".png"; // Default file extension
			dlg.Filter = "Image file (*.png) | *.png"; // Filter files by extension

			// Show save file dialog box
			Nullable<bool> result = dlg.ShowDialog();

			// Process save file dialog box results
			if (result == true)
			{

				dlg.InitialDirectory = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments);
				WebClient webClient = new WebClient();
				webClient.DownloadFileCompleted += new AsyncCompletedEventHandler(Completed);
				//webClient.DownloadProgressChanged += new DownloadProgressChangedEventHandler(ProgressChanged);
				webClient.DownloadFileAsync(new Uri("https://assets.onestore.ms/cdnfiles/external/uhf/long/9a49a7e9d8e881327e81b9eb43dabc01de70a9bb/images/microsoft-gray.png"),
					dlg.FileName);
				// Save document
				string filename = dlg.FileName;
			}



			

		}

		private void Completed(object sender, AsyncCompletedEventArgs e)
		{
			MessageBox.Show("Download completed!");
		}

	}
	}