How to check List() is empty

Question

3.00/5 (2 votes)

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Hi

I have

C#

s=new List<string>()

that returns

C#

""

when am using a breakpoint

Now I cant seem to validate

C#

"s"

using

C#

null

eg

C#

 if(result.s==null)
{
errorText="error"
}
else
{
//Play hangman code here
}

It always skip the if and jumps to else...

Posted 3-Oct-13 2:50am

Anele Ngqandu

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Comments

BillWoodruff 3-Oct-13 9:26am

If you are using JavaScript with C# here, please state that, and explain that, in your question.

3 solutions

Solution 1

If you check for the value of s before it is being initialized, it will be null. Since "S" is instantiated using s=new List<string>(), it can't be null.

If you want to know if s has values in it you can simply check for s.count(). If the value is 0, it means there are no values in it.

Posted 3-Oct-13 2:58am

Member 10170094

Comments

Anele Ngqandu 3-Oct-13 9:03am

s is accepting value from JavaScript, now JavaScript passed value of s=""

Solution 3

if(s.count()==0
{

}
else
{
}

Posted 4-Oct-13 2:54am

Atul Pachori

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BillWoodruff · Accepted Answer · 2013-10-03T03:15:00

When you declare a Reference Type, it is null ... until you initialize it.

So when you declare: List<string> s; // 's is null

And, when you intialize 's: s = new List<string>(); // 's is not null, internal List has #0 elements.

You can check for both the case of 'null and internal List having #0 elements like this:

C#

if (s == null || s.Count == 0)
 {
     errorText = "error";
 }
 else
 {
     // playHangman(?, ? ... ?);
 }

This code takes advantage of the fact that at run-time .NET will evaluate the first logical term in an 'if statement OR test and return 'true if it evaluates to 'true without evaluating the second term of the OR test.

If you tried to access the Count Property of 's when it was declared, but not initialized, that would cause an error.

However, if you are certain you have initialized 's, then you can just use (s.Count == 0) for your test expression.