c# list in property which is array

Question

This is my property class:

 class Actions
 {
     public string[] Style { get; set; }
 }

and this is my main method:

Actions action = new Actions();

List<string> list = new List<string>();
list.Add("one");
list.Add("two");

foreach (var item in list)
{
    for (int i = 0; i < action.Style.Length; i++)
    {
        action.Style[i] = item.ToString();
        Console.WriteLine(action.Style[i]);
    }                  
}

How do I fill the property with list items?

This gives me a exception:
"object reference not set to an instance of an object".

Not sure if Actions is the most appropriate name for your class. It should really be a singular word. Obviously Action is not permitted, so you might want to think of something more descriptive. — openshac, Nov 16 '16 at 17:06
May I'm wrong, but with the second list item you will overwrite the content of your style... Is this intended? And you iterate over your array, but what size has this array? Code looks confusing. — dannyyy, Nov 16 '16 at 17:12
Possible duplicate of [What is a NullReferenceException, and how do I fix it?](http://stackoverflow.com/questions/4660142/what-is-a-nullreferenceexception-and-how-do-i-fix-it) — Owen Pauling, Nov 16 '16 at 17:16

paul · Answer 1 · 2016-11-16T17:02:12.813

1

There is no need to add your items one by one, you could just use the ToArray() method of your list like so:

List<string> list = new List<string>();
list.Add("one");
list.Add("two");

Actions action = new Actions {
    Style = list.ToArray()
};

edited Nov 16 '16 at 17:02

answered Nov 16 '16 at 17:00

paul

20,643
1
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53

depends if the original problem is "how to fill property with list items?" – paul Nov 16 '16 at 17:06
the problem was that the `Style` was not instantiated – Alex Nov 16 '16 at 17:07
@Alex how to see the output of Style property? – Arman Nov 16 '16 at 17:42

score 0 · Answer 2 · edited Nov 16 '16 at 18:23

0

You must create an instance of the Style property

List<string> list = new List<string>();
list.Add("one");
list.Add("two");
Actions action = new Actions();
action.Style=new string[list.Count];

foreach (var item in list)
{
    for (int i = 0; i < action.Style.Length; i++)
    {
        action.Style[i] = item.ToString();
        Console.WriteLine(action.Style[i]);
    }                  
}

edited Nov 16 '16 at 18:23

David

3,810
2
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answered Nov 16 '16 at 17:49

Eldaniz Ismayilov

814
6
16

David · Answer 3 · 2016-11-16T18:21:22.853

As has already been pointed out, Style is always null, given the code you have shared. @Eldeniz and @paul have shared different ways to fix that. Obviously, your sample code is just a sample fragment, so here are 2 other options you could consider if the previous two don't work for whatever reason (I'm just free-handing this, please excuse any typos).

1) You can have your Actions class always return a not-null object

class Actions
{
    private string[] _style;
    public string[] Style 
    {
        get { return _style ?? new string[0]; }
        set { _style = value; }
    }
}

Note that this will allow you to always see the output of the style property as requested, assuming an empty array and null are, for your purposes, the same thing.

2) You can make your loop tolerant to null values

foreach (var item in list)
{
    for (int i = 0; i < action?.Style.Length ?? 0; i++)
    {
        action.Style[i] = item.ToString();
        Console.WriteLine(action.Style[i]);
    }                  
}

Finally, just as a tip, if you have your debugger attached and you are stepping through your code, Visual Studio will help you pinpoint these sorts of errors pretty easily. Take the time to become friends with your debugger. If it gives you an error you don't understand, do a quick web search. Your future self will thank you.

c# list in property which is array

3 Answers3