How to check if the value is null or not

Question

1.00/5 (2 votes)

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C#

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

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'

Posted 19-Oct-11 2:21am

pratheep7

Updated 19-Oct-11 2:24am

Toniyo Jackson

v2

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Comments

Xeshan Ahmed 19-Oct-11 8:28am

by the way u wrote wrong code
get
{
if (statusMessage.Message !=null)
return statusMessage.Message;
}
this is error free now

BillWoodruff 19-Oct-11 9:07am

In addition to the obvious typo of using '=!' instead of '!=' in the OP ... I would note that in the solutions proposed below (some of which will never compile because the 'get does not return a value in every case) ...

There's an assumption that StatusMessage.Message returns a string ... while that does seem like the most likely scenario here ... I'd note it's not the only one possible.

Simon Bang Terkildsen 19-Oct-11 10:53am

Very true, the OP should have posted the entire property signature.

8 solutions

Solution 2

simply use

C#

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

Posted 19-Oct-11 2:26am

Xeshan Ahmed

Comments

Simon Bang Terkildsen 19-Oct-11 8:27am

and what if statusMessage is null which is the OP's problem. And why not return null or an empty string? what would you return instead?
Though I fell into that trap as well, the OP is testing statusMessage.Message but needs to test statusMessage

Xeshan Ahmed 19-Oct-11 8:30am

it will depend upon the logic of programmer i just solved his problem

Simon Bang Terkildsen 19-Oct-11 8:38am

You're completely right I completely misunderstood the core of the question, multiple times :)

Xeshan Ahmed 19-Oct-11 9:57am

its ok Simon Bang Terkildsen

Simon Bang Terkildsen 19-Oct-11 10:42am

Thank you, Xeshan :)

Xeshan Ahmed 19-Oct-11 8:32am

it can be like this
string.IsNullOrEmpty(statusMessage.Message)?"Error":statusMessage.Message;
Error is just example use any default message

Solution 3

Use != instead of =!.

C#

if (statusMessage.Message != null)

Posted 19-Oct-11 2:27am

Toniyo Jackson

Comments

Shmuel Zang 19-Oct-11 8:55am

That's the answer. You got my 5.

Toniyo Jackson 19-Oct-11 9:02am

Thanks Shmuel :)

Solution 4

statusMessage.Message is string
and you are returning statusMessage.Message in a bool property
change the datatype bool to string of the property
and then use the following

C#

get {
         if (!string.IsNullOrEmpty(statusMessage.Message))
               return statusMessage.Message;
    }

Posted 19-Oct-11 2:31am

sachin10d

Comments

Simon Bang Terkildsen 19-Oct-11 10:43am

wont compile you have to return some value in the case when !string.IsNullOrEmpty(statusMessage.Message) is false

sachin10d 20-Oct-11 2:13am

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

Solution 7

Just another way is to use the ?? operator[^].

C#

get
{
  return statusMessage.Message ?? string.Empty;
}

It returns the string in statusMessage.Message if it is not null. If statusMessage.Message is null, it returns string.Empty.

Posted 22-Oct-11 4:11am

Kim Togo

Solution 8

the best practice to check a string is null or not
is to use:

C#

if(string.IsNullOrEmpty(StringVariable))
   {
     // some thing to do if it is null

    }

you cant not return a string variable with null value
from a property that returns a string data type
so you can do like this :

C#

get
{
if(!string.IsNullOrEmpty(StringVariable
 return StringVariable;
return string.Empty; //the empty string or return another error string

}

if you want to check an object if is null or not try:

C#

if(obj!=null)

or

C#

if(obj==null)

Posted 22-Oct-11 6:41am

Ibrahim Hebish

Solution 5

if u are using a property type, then use [Serializable] key and write the above code

then it works

Posted 19-Oct-11 2:42am

vamforvamsi

Comments

Simon Bang Terkildsen 19-Oct-11 10:46am

huh? where do the SerializableAttribute come into the picture? it will have no effect what so ever on the OP's problem, all SerializableAttribute does is telling anyone, who is interested, that a type is serializable.

Solution 6

I think you are using property only with get attribute please assign the set attribute as well so that it will work for you syntax is given
set { Message = value; }

Posted 19-Oct-11 2:52am

AlokZanwar1985

Comments

Simon Bang Terkildsen 19-Oct-11 10:47am

The error message the OP received "StatusMessage.Message cannot be assigned to -- it is read only" indicates that StatusMessage.Message is read only, this you cannot give it a value like you suggest.

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Simon Bang Terkildsen · Accepted Answer · 2011-10-19T02:25:00

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

C#

if (statusMessage != null)

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

C#

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

Assuming statusMessage is never null you would do it like so

C#

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

}

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 =

How to check if the value is null or not

8 solutions

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