How to convert this php if statement in c#?

Question

I made a code with php and now I'm trying to convert this in C#, but it isn't working

This is the php code:

ERROR:

An unhandled exception of type 'System.NullReferenceException' occurred in connectiondb.exe

Additional information: De objectverwijzing is niet op een exemplaar van een object ingesteld.

In C# there's something wrong with the: if statement, but I can't find the problem. Can someone help me?

Nothing wrong with the `if`, problem is the collection `tweedeVerzameling` it is null — sujith karivelil, Jun 15 '16 at 13:59
@Test It is *not* "useless". Understanding what a `NullReferenceException` is will help you fix the problem in your code. — Nasreddine, Jun 15 '16 at 14:01
Are your sure that it needs to be null ? or just empty ? This is a huge difference. Please look at the given link from @Nasreddine — Constantin Treiber, Jun 15 '16 at 14:04
@Test If it need to be null, why test if it contains anything ? If you meant it _could_ be null try this condition instead `if (tweedeVerzameling != null && !tweedeVerzameling.Contains(element))` — Irwene, Jun 15 '16 at 14:04
empty is NOT the same as null, one means there is a collection with 0 elements, the other says that there isn't even a collection — Irwene, Jun 15 '16 at 14:05
I think it needs to be empty, because when it's null, I get the wrong answer. Sorry! — Test, Jun 15 '16 at 14:07

score 1 · Answer 1 · edited May 23 '17 at 12:22

As he mentioned in the comment, this will explain that very clearly, Letme add few more words. In C# you will get NullReference Exception only when you are accessing value from null(Which means not existing).

Consider the following scenario:

You are assigning a work to the compiler to take check/iterate a collection. When compiler is going to do that process he is not able to find the location that you specified. Then it returns to you with the message that the specified thing is not found, i cannot proceed the action. You are getting this response message from the compiler as exception.

In the example that you have given, You are assigning the task "Iterate the Something that is null/ search something inside a memory location that is null. both are not possible since they are not existing in the memory.

What you can do to avoid this is, check for null before accessing the the value: consider the following changes in the signature:

public bool isDeelverzamelingVan(List<int> eersteVerzameling, List<int> tweedeVerzameling)
{
    if(eersteVerzameling==null || tweedeVerzameling==null)
    {
        return false;
    }
    foreach (int element in eersteVerzameling)
    {
        if (!tweedeVerzameling.Contains(element))
        {
           return false;
        }         
    }
    return true;
}

So the output will be false if anyone of the collection is null; and hence you can avoid throwing exception

I tried this, but now is restOfArray the value null: foreach (int rid in receptIDS) { restOfArray = string.Join(",", receptIDS); } label3.Text = restOfArray.ToString(); — Test, Jun 15 '16 at 14:24
I edit it, It's not everything, but I think you don't need the another code. — Test, Jun 15 '16 at 14:33

How to convert this php if statement in c#?

1 Answers1