增加string.TrimString扩展方法，可以去除头尾给定字符串

Falcon.SugarApi.Test/StringExtendTest.cs

@@ -112,5 +112,22 @@ namespace Falcon.SugarApi.Test
             Assert.IsTrue(result.Length == 1);
             Assert.IsTrue(result[0] == "abc");
         }
+
+        /// <summary>
+        /// 去除头尾字符
+        /// </summary>
+        [TestMethod]
+        public void TestTrimString() {
+            var str = @"abcabcffe222256256";
+            //去除头部的abc字符
+            var r = str.TrimString("abc");
+            Assert.AreEqual(r , "ffe222256256");
+            //去除尾部256字符
+            r = str.TrimString("","256");
+            Assert.AreEqual(r,"abcabcffe222");
+            //去除头部abc字符和尾部256字符
+            r = str.TrimString("abc","256");
+            Assert.AreEqual(r,"ffe222");
+        }
     }
 }

Falcon.SugarApi/StringExtend.cs

@@ -148,5 +148,38 @@ namespace Falcon.SugarApi
                 i += length;
             }
         }
+
+        /// <summary>
+        /// 从字符串开头去除startStr字符串并从末尾去除endStr字符串，如果有多个会全部去除。
+        /// </summary>
+        /// <param name="str">原始字符串</param>
+        /// <param name="startStr">开始处要去除的字符串，不需要则传入空字符串</param>
+        /// <param name="endStr">末尾处要去除的字符串，不需要则传入空字符串</param>
+        /// <returns>结果字符串</returns>
+        public static string TrimString(this string str,string startStr = "",string endStr = "") {
+            if(str == "") {
+                return str;
+            }
+            if(startStr != "") {
+                while(true) {
+                    var p = str.IndexOf(startStr);
+                    if(p < 0) {
+                        break;
+                    }
+                    str = str.Substring(p + startStr.Length);
+                }
+            }
+            if(endStr != "") {
+                while(true) {
+                    var p = str.LastIndexOf(endStr);
+                    if(p < 0) {
+                        break;
+                    }
+                    str = str.Substring(0,p);
+                }
+            }
+            return str;
+        }
+
     }
 }