Assign a value from a string array to the string property of each element of a custom type array

Question

Suppose I have an array of strings - countryNames[] - containing the names of the countries in the world:

string[] countryNames = { "Afghanistan" , "Albania" , "Algeria", ... }

I also have a class called Country containing these properties, among others:

public string CountryCode { get; set; }
public string Name { get; set; }

My goal is to create an array of the custom type Country, and assign to the Country.Name property of each element of Country[] the corresponding index's string value of countryNames[]. I tried doing so in the following way, in the same method where I implemented the string array:

Country[] countries = new Country[193];
for (int i = 0; i < 193; i++)
{
    countries[i].Name = countryNames[i];
}
return countries;

The countries[i].Name however, causes a NullReferenceException . I can't see where the problem is though, as the property Country.Name is a string. Are there any complications when arrays and properties are mixed together?

Thanks guys!

Only initialization of array will not suffice. You have to create country objects before entering the for loop and add them in array. Then you can assign value to Name property of each country. — Sagar
– Sagar, Commented Sep 1, 2016 at 13:15

Gilad Green · Accepted Answer · 2016-09-01 13:20:14Z

6

The reason why you get a NullReferenceException is that when you initialize an array of object it doesn't initialize the items within it. Meaning that when you access countries[i].Name that object doesn't exist, and then .Name throws the exception.

So you need to initialize it:

for (int i = 0; i < 193; i++)
{
    countries[i] = new Country { Name = countryNames[i] };
}

A better way that using a for loop is using a foreach:

List<Country> countries = new List<Country>();
foreach(var countryName in countryNames
{
    countries.Add(new Country { Name = countryName });
}

And then from the foreach you can leap to linq:

string[] countryNames = { "Afghanistan", "Albania", "Algeria" };
var countried = countryNames.Select(item => new Country { Name = item });

edited Sep 1, 2016 at 13:20

answered Sep 1, 2016 at 13:15

Gilad Green

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1 Comment

Renato Over a year ago

Thanks. The Linq method is even better as it does the job in a single line of code!

Stefan · Accepted Answer · 2016-09-01 13:14:51Z

2

You should make a new Country first:

Country[] countries = new Country[193];

for (int i = 0; i < 193; i++)
{
    countries[i] = new Country();
    countries[i].Name = countryNames[i];
}

return countries;

By doing:

Country[] countries = new Country[193];

You are only reserving space for the array, the individual elements are initialized to null

answered Sep 1, 2016 at 13:14

Stefan

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