/// <summary>  /// 將字符串轉(zhuǎn)換成32位整數(shù),轉(zhuǎn)換失敗返回null  /// </summary>  /// <param name="str">轉(zhuǎn)換的字符串</param>  /// <returns>轉(zhuǎn)換之后的整數(shù),或null</returns>  public static int? TryParseToInt32(this string str)  {    if (string.IsNullOrWhiteSpace(str))      return null;    var result = 0;    if (int.TryParse(str, out result))      return result;    else      return null;  }

  /// <summary>  /// 去除子字符串  /// </summary>  /// <param name="str">原字符串</param>  /// <param name="substring">要去除的字符串</param>  /// <returns>去除子字符串之后的結(jié)果</returns>  public static string DeSubstring(this string str, string substring)  {    if (string.IsNullOrEmpty(str) || string.IsNullOrEmpty(substring) || !str.Contains(substring))    {      return str;    }    return Regex.Replace(str, Regex.Escape(substring), string.Empty);  }  /// <summary>  /// 去除子字符串  /// </summary>  /// <param name="str">原字符串</param>  /// <param name="substrings">要去除的子字符串</param>  /// <returns>去除子字符串之后的結(jié)果</returns>  public static string DeSubstring(this string str, params string[] substrings)  {    if (string.IsNullOrEmpty(str))      return str;    if (substrings == null)      return str;    var newStr = str;    foreach (var item in substrings)    {      newStr = newStr.DeSubstring(item);    }    return newStr;  }

  /// <summary>  /// 獲取子序列  /// </summary>  /// <typeparam name="T">序列中元素類型</typeparam>  /// <param name="source">源數(shù)據(jù)</param>  /// <param name="startIndex">開始索引(返回時(shí)包括)</param>  /// <param name="endIndex">結(jié)束索引(返回時(shí)包括)</param>  /// <returns>子序列</returns>  public static IEnumerable<T> SubEnumerable<T>(this IEnumerable<T> source, int startIndex, int endIndex)  {    if (source == null)      yield return default(T);    var length = source.Count();    if (startIndex < 0 || endIndex < startIndex || startIndex >= length || endIndex >= length)      throw new ArgumentOutOfRangeException();    var index = -1;    foreach (var item in source)    {      index++;      if (index < startIndex)        continue;      if (index > endIndex)        yield break;      yield return item;    }  }

  /// <summary>  /// 通過對(duì)指定的值進(jìn)行比較返回序列中的非重復(fù)元素。  /// </summary>  /// <typeparam name="T">序列中元素類型</typeparam>  /// <typeparam name="TResult">指定的比較屬性類型</typeparam>  /// <param name="source">源數(shù)據(jù)</param>  /// <param name="selector">應(yīng)用于每個(gè)元素的轉(zhuǎn)換函數(shù)</param>  /// <returns>一個(gè)包含源序列中的按指定屬性非重復(fù)元素</returns>  public static IEnumerable<T> Distinct<T, TResult>(this IEnumerable<T> source, Func<T, TResult> selector)  {    if (source == null)      throw new ArgumentNullException(nameof(source));    if (selector == null)      throw new ArgumentNullException(nameof(selector));    var set = new HashSet<TResult>();    foreach (var item in source)    {      var result = selector(item);      if (set.Add(result))      {        yield return item;      }    }  }

  /// <summary>  /// 通過對(duì)指定的值進(jìn)行比較返回序列中重復(fù)的元素  /// </summary>  /// <typeparam name="T">序列中的數(shù)據(jù)類型</typeparam>  /// <typeparam name="TResult">指定的比較屬性類型</typeparam>  /// <param name="source">源數(shù)據(jù)</param>  /// <param name="selector">應(yīng)用于每個(gè)元素的轉(zhuǎn)換函數(shù)</param>  /// <returns>一個(gè)包含源序列中的按指定元素的重復(fù)元素</returns>  public static IEnumerable<T> Identical<T>(this IEnumerable<T> source)  {    if (source == null)      throw new ArgumentNullException(nameof(source));    var setT = new HashSet<T>();    foreach (var item in source)    {      if (!setT.Add(item))      {        yield return item;      }    }  }  /// <summary>  /// 通過對(duì)指定的值進(jìn)行比較返回序列中重復(fù)的元素  /// </summary>  /// <typeparam name="T">序列中的數(shù)據(jù)類型</typeparam>  /// <typeparam name="TResult">指定的比較屬性類型</typeparam>  /// <param name="source">源數(shù)據(jù)</param>  /// <param name="selector">應(yīng)用于每個(gè)元素的轉(zhuǎn)換函數(shù)</param>  /// <returns>一個(gè)包含源序列中的按指定元素的重復(fù)元素</returns>  public static IEnumerable<T> Identical<T, TResult>(this IEnumerable<T> source, Func<T, TResult> selector)  {    if (source == null)      throw new ArgumentNullException(nameof(source));    if (selector == null)      throw new ArgumentNullException(nameof(selector));    var setTResult = new HashSet<TResult>();    foreach (var item in source)    {      var result = selector(item);      if (!setTResult.Add(result))      {        yield return item;      }    }  }