/// <summary>
/// 取文本中间内容
/// </summary>
/// <param name="str">原文本</param>
/// <param name="leftstr">左边文本</param>
/// <param name="rightstr">右边文本</param>
/// <returns>返回中间文本内容</returns>
public static string Between(string str, string leftstr, string rightstr)
{
    int i = str.IndexOf(leftstr) + leftstr.Length;
    string temp = str.Substring(i, str.IndexOf(rightstr, i) - i);
    return temp;
}