String.IsNullOrEmpty
指示指定的字符串是否为 null 或者 空字符串;
返回值:如果参数为 null 或者 空字符串("" 、String.Empty),结果为true,否则为false。
等效于以下代码:
result = s == null || s == String.Empty;
String.IsNullOrWhiteSpace
指示指定的字符串是否为 null、空字符串 或者 仅由空字符组成。
返回值:如果参数为 null 、 空字符串("" 、String.Empty) 或者 仅由空字符组成,结果为true,否则为false。
等效于以下代码:
result = String.IsNullOrEmpty(s) || s.Trim().Length == 0;
测试代码:
1 string s1 = null; 2 string s2 = string.Empty; 3 string s3 = ""; 4 string s4 = " "; 5 string s5 = " "; 6 7 try 8 { 9 Console.WriteLine("The length of '{0}' is {1}.", s1, s1.Length); 10 } 11 catch (NullReferenceException ex) 12 { 13 Console.WriteLine(ex.Message); 14 } 15 Console.WriteLine("The length of '{0}' is {1}.", s2, s2.Length); 16 Console.WriteLine("The length of '{0}' is {1}.", s3, s3.Length); 17 Console.WriteLine("The length of '{0}' is {1}.", s4, s4.Length); 18 Console.WriteLine("The length of '{0}' is {1}.", s5, s5.Length); 19 20 Console.WriteLine("-------------------------------------------------------"); 21 22 Console.WriteLine(string.IsNullOrEmpty(s1)); 23 Console.WriteLine(string.IsNullOrEmpty(s2)); 24 Console.WriteLine(string.IsNullOrEmpty(s3)); 25 Console.WriteLine(string.IsNullOrEmpty(s4)); 26 Console.WriteLine(string.IsNullOrEmpty(s5)); 27 28 Console.WriteLine("-------------------------------------------------------"); 29 30 Console.WriteLine(string.IsNullOrWhiteSpace(s1)); 31 Console.WriteLine(string.IsNullOrWhiteSpace(s2)); 32 Console.WriteLine(string.IsNullOrWhiteSpace(s3)); 33 Console.WriteLine(string.IsNullOrWhiteSpace(s4)); 34 Console.WriteLine(string.IsNullOrWhiteSpace(s5));
结果:
未将对象引用设置到对象的实例。
The length of '' is 0.
The length of '' is 0.
The length of ' ' is 4.
The length of ' ' is 1.
-------------------------------------------------------
True
True
True
False
False
-------------------------------------------------------
True
True
True
True
True
相关资料:
https://msdn.microsoft.com/zh-cn/library/system.string.isnullorempty(v=vs.110).aspx
https://msdn.microsoft.com/zh-cn/library/system.string.isnullorwhitespace(v=vs.110).aspx