private string SelectPath() //弹出一个选择目录的对话框
{
     FolderBrowserDialog path = new FolderBrowserDialog();
     path.ShowDialog();
     return path.SelectedPath;
}
private string SelectFile() //弹出一个选择文件的对话框
{
     OpenFileDialog file = new OpenFileDialog();
     file.ShowDialog();
     return file.SafeFileName;
}