C# 中 IsNullOrEmpty 和 IsNullOrWhiteSpace 的区别

Difference between IsNullOrEmpty and IsNullOrWhiteSpace in C#

提问by Asieh hojatoleslami

What are differences between these commands in C#

C#中这些命令有什么区别

string text= "  ";
1-string.IsNullOrEmpty(text.Trim())

2-string.IsNullOrWhiteSpace(text)

采纳答案by fionbio

• Source: MSDN

• 来源：MSDN

IsNullOrWhiteSpaceis a convenience method that is similar to the following code, except that it offers superior performance:

return String.IsNullOrEmpty(value) || value.Trim().Length == 0;

White-space characters are defined by the Unicode standard. The IsNullOrWhiteSpacemethod interprets any character that returns a value of true when it is passed to the Char.IsWhiteSpacemethod as a white-space character.

IsNullOrWhiteSpace是一种类似于以下代码的便捷方法，不同之处在于它提供了卓越的性能：

return String.IsNullOrEmpty(value) || value.Trim().Length == 0;

空白字符由 Unicode 标准定义。该 IsNullOrWhiteSpace方法将在传递给该Char.IsWhiteSpace方法时返回值为 true 的任何字符解释为空白字符。

回答by TGH

The first method checks if a string is null or a blank string. In your example you can risk a null reference since you are not checking for null before trimming

第一个方法检查字符串是空字符串还是空字符串。在您的示例中，您可能会冒空引用的风险，因为您在修剪之前没有检查空值

1- string.IsNullOrEmpty(text.Trim())

The second method checks if a string is null or an arbitrary number of spaces in the string (including a blank string)

第二种方法检查字符串是否为空或字符串中的任意数量的空格（包括空字符串）

2- string .IsNullOrWhiteSpace(text)

The method IsNullOrWhiteSpacecovers IsNullOrEmpty, but it also returns trueif the string contains white space.

该方法IsNullOrWhiteSpace涵盖IsNullOrEmpty，但true如果字符串包含空格，它也会返回。

In your concrete example you should use 2) as you run the risk of a null reference exception in approach 1) since you're calling trim on a string that may be null

在您的具体示例中，您应该使用 2) 因为您在方法 1) 中冒着空引用异常的风险，因为您正在对可能为空的字符串调用 trim

回答by JHubbard80

String.IsNullOrEmpty(string value)returns trueif the string is null or empty. For reference an empty string is represented by "" (two double quote characters)

String.IsNullOrEmpty(string value)true如果字符串为 null 或为空，则返回。作为参考，空字符串由“”（两个双引号字符）表示

String.IsNullOrWhitespace(string value)returns trueif the string is null, empty, or contains only whitespace characters such as a space or tab.

String.IsNullOrWhitespace(string value)返回true如果字符串是空，空，或仅包含空白字符，例如一个空格或标签。

To see what characters count as whitespace consult this link: http://msdn.microsoft.com/en-us/library/t809ektx.aspx

要查看哪些字符算作空格，请参阅此链接：http: //msdn.microsoft.com/en-us/library/t809ektx.aspx

回答by fubo

Short answer:

简短的回答：

In common use, space " ", Tab "\t"and newline "\n"are the difference:

常用的空格" "、制表符"\t"和换行符"\n"的区别是：

string.IsNullOrWhiteSpace("\t"); //true
string.IsNullOrEmpty("\t"); //false

string.IsNullOrWhiteSpace(" "); //true
string.IsNullOrEmpty(" "); //false

string.IsNullOrWhiteSpace("\n"); //true
string.IsNullOrEmpty("\n"); //false

https://dotnetfiddle.net/4hkpKM

https://dotnetfiddle.net/4hkpKM

also see this answer about: whitespace characters

另请参阅有关以下内容的答案：空白字符

---

---

Long answer:

长答案：

There are also a few other white space characters, you probably never used before

还有一些其他的空白字符，您可能以前从未使用过

https://docs.microsoft.com/en-us/dotnet/api/system.char.iswhitespace

https://docs.microsoft.com/en-us/dotnet/api/system.char.iswhitespace

回答by CloudyMarble

If your string (In your case the variable text) could be null this would make a big Difference:

如果您的字符串（在您的情况下是变量text）可能为空，这将产生很大的不同：

1-string.IsNullOrEmpty(text.Trim())--> EXCEPTIONsince your calling a mthode of a null object

1- string.IsNullOrEmpty(text.Trim())-->异常，因为您调用了空对象的方法

2-string.IsNullOrWhiteSpace(text)This would work fine since the null issue is beeing checked internally

2-string.IsNullOrWhiteSpace(text)这可以正常工作，因为正在内部检查 null 问题

To provide the same behaviour using the 1st Option you would have to check somehow if its not null first then use the trim() method

要使用第一个选项提供相同的行为，您必须先检查它是否不为空，然后使用 trim() 方法

if ((text != null) && string.IsNullOrEmpty(text.Trim())) { ... }

回答by ?ubo? ?urgó

This is implementation of methodsafter decompiling.

这是反编译后方法的实现。

    public static bool IsNullOrEmpty(String value) 
    {
        return (value == null || value.Length == 0); 
    }

    public static bool IsNullOrWhiteSpace(String value) 
    {
        if (value == null) return true; 

        for(int i = 0; i < value.Length; i++) { 
            if(!Char.IsWhiteSpace(value[i])) return false; 
        }

        return true;
    }

So it is obvious that IsNullOrWhiteSpacemethod also checks if value that is being passed contain white spaces.

所以很明显IsNullOrWhiteSpace方法还检查传递的值是否包含空格。

Whitespaces refer : https://msdn.microsoft.com/en-us/library/system.char.iswhitespace(v=vs.110).aspx

空格是指：https://msdn.microsoft.com/en-us/library/system.char.iswhitespace( v=vs.110).aspx

回答by vibs2006

string.isNullOrWhiteSpace(text)should be used in most cases as it also includes a blank string.

string.isNullOrWhiteSpace(text)应该在大多数情况下使用，因为它也包含一个空白 string。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;
namespace Rextester
{
    public class Program
    {
        public static void Main(string[] args)
        {
            //Your code goes here
            var str = "";

            Console.WriteLine(string.IsNullOrWhiteSpace(str));              

        }
    }
}

It returns True!

它返回True！

回答by Italo Pacheco

[Performance Test] just in case anyone is wondering, in a stopwatch test comparing

[性能测试] 以防万一有人想知道，在秒表测试中比较

if(nopass.Trim().Length > 0)

if(nopass.Trim().Length > 0)

if (!string.IsNullOrWhiteSpace(nopass))

if (!string.IsNullOrWhiteSpace(nopass))

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these were the results:

结果如下：

Trim-Length with empty value = 15

修剪长度为空值 = 15

Trim-Length with not empty value = 52

修剪长度不为空值 = 52

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IsNullOrWhiteSpace with empty value = 11

IsNullOrWhiteSpace 空值 = 11

IsNullOrWhiteSpace with not empty value = 12

IsNullOrWhiteSpace 非空值 = 12