C#设置默认打印机

<Window x:Class="PrintersApp.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <StackPanel>
            <ComboBox x:Name="printerComboBox"/>
            <Button Content="设置成打印机" Click="setDefaultPrintBtn"/>
        </StackPanel>
    </Grid>
</Window>

 public class LocalPrinter
    {
        private static PrintDocument fPrintDocument = new PrintDocument();
        //获取本机默认打印机名称
        public static String DefaultPrinter()
        {
            return fPrintDocument.PrinterSettings.PrinterName;
        }
        public static List<String> GetLocalPrinters()
        {
            List<String> fPrinters = new List<String>();
            fPrinters.Add(DefaultPrinter()); //默认打印机始终出现在列表的第一项
            foreach (String fPrinterName in PrinterSettings.InstalledPrinters)
            {
                if (!fPrinters.Contains(fPrinterName))
                {
                    fPrinters.Add(fPrinterName);
                }
            }
            return fPrinters;
        }
    }

  public class Externs
   {
       [DllImport("winspool.drv")]
       public static extern bool SetDefaultPrinter(String Name); //调用win api将指定名称的打印机设置为默认打印机
   }

   /// <summary>
    /// MainWindow.xaml 的交互逻辑
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            InitprinterComboBox(); //初始化打印机下拉列表选项
        }

        private void InitprinterComboBox()
        {
            List<String> list = LocalPrinter.GetLocalPrinters(); //获得系统中的打印机列表
            foreach (String s in list)
            {
                printerComboBox.Items.Add(s); //将打印机名称添加到下拉框中
            }
        }

        private void setDefaultPrintBtn(object sender, RoutedEventArgs e)
        {
            if (printerComboBox.SelectedItem != null) //判断是否有选中值
            {
                if (Externs.SetDefaultPrinter(printerComboBox.SelectedItem.ToString())) //设置默认打印机
                {
                    MessageBox.Show(printerComboBox.SelectedItem.ToString() + "设置为默认打印机成功！");
                }
                else
                {
                    MessageBox.Show(printerComboBox.SelectedItem.ToString() + "设置为默认打印机失败！");
                }
            }

        }
    }