GetParentDirectoryPath

public static class stringExtends
{

	/// <summary>
	/// 取得某目錄的上幾層的目錄路徑
	/// </summary>
	/// <param name="folderPath">目錄路徑</param>
	/// <param name="levels">要往上幾層</param>
	/// <returns></returns>
	public static string GetParentDirectoryPath(this string folderPath, int levels)
    {
        string result = folderPath;
        for (int i = 0; i < levels; i++)
        {
            if (Directory.GetParent(result) != null)
            {
                 result = Directory.GetParent(result).FullName;
            }
            else
            {
                return result;
            }        
        }
        return result;
    }

	/// <summary>
	/// 取得某目錄的上層的目錄路徑
	/// </summary>
	/// <param name="folderPath">目錄路徑</param>
	/// <returns></returns>
	public static string GetParentDirectoryPath(this string folderPath)
	{
		return GetParentDirectoryPath(folderPath, 1);
	}

	/// <summary>
	/// 取得路徑的目錄路徑
	/// </summary>
	/// <param name="filePath">路徑</param>
	/// <returns></returns>
	public static string GetDirectoryPath(this string filePath)
	{
		return Path.GetDirectoryName(filePath);
	}
}

MessageBox.Show(Application.ExecutablePath.GetDirectoryPath().GetParentDirectoryPath());
MessageBox.Show(Application.ExecutablePath.GetDirectoryPath().GetParentDirectoryPath(2));