Why I am getting null exception when using an Interface

Question

public class Blah
{
    public bool Whatever { get; set; }
    public string WhatYouJustSaid { get; set; }
}

public interface IBlah
{
    Blah BlahValues { get; set; }
}

class Class1:IBlah
{
    public Blah BlahValues { get; set; }
}

And then for example:

   Class1 c1 = new Class1();
   c1.BlahValues.WhatYouJustSaid = "nothing";
    c1.BlahValues.Whatever = false;

So how should I change my code that BlahValues doesn't get null?

This has nothing to do with the fact that you're using an interface. You have a property that you you never initialized. Of course it'll be null. You have to assign a value to BlahValues — Jonesopolis, Apr 21 '16 at 19:25

score 1 · Accepted Answer · answered Apr 21 '16 at 19:23

1

You have to initialize the BlahValues. Using an object initializer, this can be done as below:

Class1 c1 = new Class1()
{
   BlahValues = new Blah() 
};

As you create the c1 object, the BlahValues get it's default value, which is null. Hence, when you try to assign a value to WhatYouJustSaid and Whatever you get a null reference exception.

answered Apr 21 '16 at 19:23

Christos

50,311
8
62
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Can you take a look at this question I had please ? In that question I was using Ninject and NSubstitute and getting a null exception crash which first I thought it is becuase I am new to both of those but then I recreated the way I am using interfaces in this question and got the same null exception. So maybe you can help with my actual question here too ? http://stackoverflow.com/questions/36777185/using-nsubstitute-and-ninject-to-return-a-value – Bohn Apr 21 '16 at 19:29

score 0 · Answer 2 · answered Apr 21 '16 at 19:25

0

use it like this inside the constructor of Class1

public  Class1()
{
    this.BlahValues = new Blah() 
}

answered Apr 21 '16 at 19:25

rashfmnb

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4
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Why I am getting null exception when using an Interface

2 Answers2