String.IsNullOrEmpty 与 String.IsNullOrWhiteSpace

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