CODEWITHSUNDEEP
c#asp.net.net-3.5
venkat
venkat

Reputation: 5738

How to check object is null or empty in C#.NET 3.5?

If objects contains null or empty then how to validate or check the condition for the same?

How to bool check whether object obj is null or Empty

I've code as follows:

class Program
{
    static void Main(string[] args)
    {
        object obj = null;

        double d = Convert.ToDouble(string.IsNullOrEmpty(obj.ToString()) ? 0.0 : obj);
        Console.WriteLine(d.ToString());
    }
}

With this code i'm getting NullReference Exception as Object reference not set to an instance of an object.

Pls help.

Here I'm not getting....

How to validate whether that object is null or Empty without converting into .ToString() ??

Is there an approach to check the same??

Upvotes: 9

Views: 80003

Answers (7)

Praveen Kumar Thalluri
Praveen Kumar Thalluri

Reputation: 1157

Following code could be a safer way of achieving it.

if(obj != null && !string.IsNullOrEmpty(obj.ToString()))
{

}

This code saves us from object being a non-string type.

Upvotes: 0

user3245067
user3245067

Reputation: 195

class Program
{
    static void Main(string[] args)
    {
        object obj = DBNull.Value;
        if(obj != DBNull.Value) {
            double d = Convert.ToDouble(obj);
            Console.WriteLine(d.ToString());
        }
    }
}

Upvotes: 2

Mohit Vashistha
Mohit Vashistha

Reputation: 1904

You can use the ?? operator. It is known as the null-coalescing operator.

Upvotes: 1

TBohnen.jnr
TBohnen.jnr

Reputation: 5129

You are getting the null reference because you are executing obj.ToString() which will return obj's ToString() method return value. Problem is that in the previous line you set obj to null so you will get an object reference not... error

To make your code work you need to do: 

//This will check if it's a null and then it will return 0.0 otherwise it will return your obj.
double d = Convert.ToDouble(obj ?? 0.0);

Your code as it is now however will always be 0.0

Without null coalescing: (??)

double d = Convert.ToDouble(obj ? 0.0 : obj);

EDIT

If I understand correctly from the comments you want to know if the object is null or an empty string. You can do this by casting it to string first instead of calling the ToString method which does something entirely different:

string objString = (obj as string);
double d = Convert.ToDouble(string.IsNullOrEmpty(objString) ? "0.0" : objString);

Upvotes: 3

Stefan H
Stefan H

Reputation: 6683

The problem that you are running into is that your object is of type, well, object. In order to evaluate it with string.IsNullOrEmpty, you should pass your object in with the cast to (string)

like so:

static void Main(string[] args)
{
    object obj = null;

    double d = Convert.ToDouble(string.IsNullOrEmpty((string)obj) ? 0.0 : obj);
    Console.WriteLine(d.ToString());
}

This will work fine since you are not explicitly calling .ToString on your (nonexistent) object.

Upvotes: 13

Dmitry S.
Dmitry S.

Reputation: 8513

It sounds like what you want to do is this:

object obj = null;
double d;

if (!double.TryParse(Convert.ToString(obj), out d))
{
   d = 0.0;
}

But the question does not make a lot of sense.

Upvotes: 1

Adam Mihalcin
Adam Mihalcin

Reputation: 14478

You shouldn't be a bit surprised that you get a NullReferenceException with this code. The offending part is

obj.ToString()

If you wrote

object obj = null;
string s = obj.ToString();

you would expect a NullReferenceException. Since the call to ToString occurs before the call to string.IsNullOrEmpty, the exception is thrown before there is a check for a null or empty string.

Upvotes: 0

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