Function to check a null string property?

Question

I have an object with string properties, for example, a Patient object with weight and height.

But when the property is null, my code fails when I try to use it, as the property is set to null. I'm trying to create a function that checks if the string/property is null, and if so, set the property to "".

I know that I can do this:

if(string.isNullOrEmpty(patient.weight)) patient.weight = "";

But I need the code to be as clean as possible, and I have a lot of properties, so I don't want to manually check each one. Ideally, I'd like to have a function that can take the string, (without failing even if it is null), and simply return either the value if it's not null, or a "" if it is null.

Can anyone give me a clue on this?

Answer 1

Personally I would ensure those properties can never be null by writing them like this:

private string _Name = string.Empty;
public string Name
{
    get
    {
        return _Name;
    }
    set
    {
        _Name = value ?? string.Empty;
    }
}

However, what you're looking for is probably the ?? operator, also known as the null-coalescing operator, as used above, basically, this expression:

x = y ?? z;

means the same as this:

if (y != null)
    x = y;
else
    x = z;

and that's not entirely true either. In the above example y is evaluated twice, which does not happen with the ?? operator so a better approximation would be this:

var temp = y;
if (temp != null)
    x = temp;
else
    x = z;

Answer 2

Well the null coalescing operator sounds like it's your friend here:

string text = patient.Name ?? "";

You could write an extension method to do the same thing, but I think the operator's likely to end up being more readable.

Note that this won't set the property - but that's not what you say you want anyway, in the sentence:

Ideally, I'd like to have a function that can take the string, (not fail even if it is null), and simply return either the value (if it's not null), or a "" if it is null.

That's exactly what the code above does.

Answer 3

Something like this ?

public string EmptyIfNull(string value) 
{
    return value ?? String.Empty;
}

Answer 4

Use the null-coalescing operator:

string s = Patient.Name ?? string.Empty;

So if Patient.Name is null, then s will be set to the empty string.

Answer 5

You can do myString ?? string.Empty, which gives you the string, or string.Empty if it is null.

Answer 6

Say hello to the null coalescing operator.

Answer 7

You can use the ?? operator to return a default value of your choice when any object is null.

string a = null;
a = a ?? "womble";
// a now has the value "womble"

string b = "fluff";
b = b ?? "cabbage";
// b wasn't null, so it still has the value "fluff"

Answer 8

If Weight and Height are integers they cannot be null. If your object is null and you are trying to get the Height of Weight of a null object then you code is simply wrong. If a string is null then it will print a null character.

The following is very elegant:

if ( String.isNullOrEmpty(patient.weight) )
{
//DO STUFF HERE
}
else
{
//DO OTHER STUFF HERE
}

Please understand if patient is null you shouldn't even be in this block of code.

If you are using isNullOrEmpty then doing the following is pointless.

patient.weight = "";

Author's Note

I guess i do not understand the reason a string being null is going to cause a problem. The points about setting the value to an empty string when intialized are of course valid.

Answer 9

I'm not sure what you are asking is the best solution for you. If every time you wan't to check a String and return "" if it is null, I'd suggest instead that you initialize your String fields to "".

private String height = "";

instead of

private String height;

By the way, you should store values like height and weight as Double and not String, unless you have a good reason not to.

Answer 10

You can take the idea from @Jon one step further so you don't have to worry about using ?? everywhere:

Define your access methods like this:

private String m_name = null;
public String Name
{
    get { return m_name ?? String.Empty; }
    set { m_name = value; }
}

Anywhere you access the Name property it will perform the null coalescing operator for you.