添加项目文件。

HT.Cloud.Code/Extend/Ext.String.cs

@@ -0,0 +1,37 @@
+using System;
+
+namespace HT.Cloud.Code
+{
+	/// <summary>
+	/// string扩展类
+	/// </summary>
+	public static partial class Extensions
+	{
+		/// <summary>
+		/// 从分隔符开始向尾部截取字符串
+		/// </summary>
+		/// <param name="this">源字符串</param>
+		/// <param name="separator">分隔符</param>
+		/// <param name="lastIndexOf">true：从最后一个匹配的分隔符开始截取，false：从第一个匹配的分隔符开始截取，默认：true</param>
+		/// <returns>string</returns>
+		public static string Substring(this string @this, string separator, bool lastIndexOf = true)
+		{
+			var startIndex = (lastIndexOf ?
+				@this.LastIndexOf(separator, StringComparison.OrdinalIgnoreCase) :
+				@this.IndexOf(separator, StringComparison.OrdinalIgnoreCase)) +
+				separator.Length;
+
+			var length = @this.Length - startIndex;
+			return @this.Substring(startIndex, length);
+		}
+		#region 字符串截取第一个
+		public static string ReplaceFrist(this string str, string oldChar, string newChar)
+		{
+			int idx = str.IndexOf(oldChar);
+			str = str.Remove(idx, oldChar.Length);
+			str = str.Insert(idx, newChar);
+			return str;
+		}
+		#endregion
+	}
+}