如何检查该值是否为空 [英] How to check if the value is null or not

问题描述

get {
                if (statusMessage.Message =!null)
                return statusMessage.Message; 
            }

我需要先检查状态消息是否为空，然后再返回.但是当我检查它时，出现以下错误.那我该如何检查它是否为空呢?

I need to check if the status message is null before returning it. but when I check it it give me the following error. then How can i check if its null or not?

StatusMessage.Message cannot be assigned to -- it is read only<br />
	<br />
Error	3	Cannot implicitly convert type ''bool?'' to ''string''	<br />
Error	4	Cannot implicitly convert type ''string'' to ''bool''

推荐答案

您正在将!null(未编译)分配给statusMessage.Message，您需要测试statusMessage表示null，然后statusMessage.Message表示

You''re assigning !null (which doesn''t compile) to statusMessage.Message You need to test statusMessage for null and then statusMessage.Message for null

if (statusMessage != null)

!必须在=
的左侧
哦，在statusMessage为null的情况下，您还需要返回其他内容

The ! has to be on the left side of the =

Oh and one more thing you need to return something else in the case when statusMessage is null

get
{
    if (statusMessage != null)
        return statusMessage.Message; 
    return string.Empty; // assuming statusMessage.Message is a string

}

假设statusMessage永远不会为null，您将像这样

Assuming statusMessage is never null you would do it like so

get
{
    if (statusMessage.Message != null) // If statusMessage can be null it must be tested aswell
        return statusMessage.Message; 
    return string.Empty; // assuming statusMessage.Message is a string

}

请记住，在statusMessage.Message为null的情况下，您必须返回其他值.
并且!必须位于=

Remember you have to return some other value in the case when statusMessage.Message is null.
And the ! has to be on the left side of the =

的左侧，只需使用

simply use

if(string.IsNullOrEmpty(statusMessage.Message))
return statusMessage.Message; 

使用！=代替=!.

Use != instead of =!.

if (statusMessage.Message != null)

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