string url = "http://avatar.csdn.net/A/2/6/2_yefengzhixia.jpg";string filepath = "D:\\pic.jpg";WebClient mywebclient = new WebClient();mywebclient.DownloadFile(url, filepath);MessageBox.Show("OK");    

<Grid><DockPanel><GroupBox x:Name="groupBox" Header="图片网址" DockPanel.Dock="Top"><StackPanel><StackPanel Orientation="Horizontal" Margin="10" ><Button x:Name="button" Content="查看网页中的图片" Margin="5" Click="button_Click"  /><TextBlock Text="网址："></TextBlock><TextBox x:Name="textBox" Text="http://www.tooopen.com/img/87.aspx" HorizontalAlignment="Left" MaxWidth="600" TextWrapping="Wrap" MinWidth="300"  VerticalAlignment="Top"  /></StackPanel><TextBlock Text="下载信息："></TextBlock><TextBlock Margin="10" Name="txtcount" Text="{Binding downCount}"></TextBlock><TextBlock Name="total"></TextBlock><Button Click="Button_Click_1" Content="打开下载图片文件夹"></Button></StackPanel></GroupBox><ListBox Name="lb"></ListBox></DockPanel></Grid>

 public partial class MainWindow : Window,INotifyPropertyChanged{public MainWindow(){InitializeComponent();this.DataContext = this;}private int c;public int downCount{get { return c; }set { c = value;if (PropertyChanged != null)PropertyChanged(this, new PropertyChangedEventArgs("downCount"));}}public ObservableCollection<string> list = new ObservableCollection<string>();public event PropertyChangedEventHandler PropertyChanged;private async void button_Click(object sender, RoutedEventArgs e){var path = textBox.Text;if (string.IsNullOrWhiteSpace(path)){textBox.Focus();MessageBox.Show("请输入网站地址");return;}HttpClient client = new HttpClient();var str = await client.GetStringAsync(new Uri(path));Regex rg = new Regex("<img.+?src=\"(.+?)\"");var mth = rg.Matches(str);WebClient wc = null;int i = 0;total.Text="共有图片："+mth.Count;Action<string> listboxAddImgName = x => {lb.Items.Add(x);};foreach (Match item in mth){i++;var img = item.Groups[1].Value;string Ex = img.Substring(img.LastIndexOf("."));string imgName = i + Ex;Task.Run(() =>{wc = new WebClient();wc.DownloadFile(img, "DownLoadImages/" + imgName);return imgName;}).ContinueWith(r=> {downCount +=1;Dispatcher.Invoke(listboxAddImgName,r.Result);});}}private void Button_Click_1(object sender, RoutedEventArgs e){System.Diagnostics.Process.Start(Environment.CurrentDirectory+"/DownLoadImages");}}

  HttpClient client = new HttpClient();var http = await client.GetStringAsync(txturl.Text.Trim());Regex rg = new Regex("<img.+?src=\"(.+?)\"");var ms = rg.Matches(http);List<Task> tasklist = new List<Task>();count = ms.Count;foreach (Match m in ms){if (m.Success){string imgurl = m.Groups[1].ToString();Task.Run(async () =>{var downImgurl = System.IO.Path.Combine(path, imgurl.Substring(imgurl.LastIndexOf(@"/") + 1));WebClient wc = new WebClient();wc.DownloadFile(imgurl, downImgurl);//byte[] buf = await client.GetByteArrayAsync(imgurl);//File.WriteAllBytes(downImgurl, buf);lock (obj){Dispatcher.Invoke(() =>{list.Add(new Img() { url = downImgurl });});num++;}});}}