C# NullReferenceException in class validation method

Question

I am trying to add a helper method to scrub out any non-alphanumeric characters in my class. However, I keep getting the error

NullReferenceException: Object reference not set to an instance of an object.

Not sure what I'm doing wrong here since I thought this was the proper way to set up any kind of validation within a class. Any suggestions would be appreciated.

    private string agentId;
    public string AgentId
    {
        get { return agentId; }
        set { agentId = this.scrubAgentId(); } 
    }

    private string scrubAgentId()
    {
        char[] arr = this.AgentId.ToCharArray();

        arr = Array.FindAll<char>(arr, (c => (char.IsLetterOrDigit(c))));
        return new string(arr);
    }

AgentId is null in scrubAgentId's char[] arr = this.AgentId.ToCharArray(); — G. Stoynev
– G. Stoynev, Commented Apr 26, 2013 at 17:49

Jordan Kaye · Accepted Answer · 2013-04-26 17:50:07Z

6

This isn't really right at all. You're discarding the value when performing your set. It should probably look something more like this:

    private string agentId;
    public string AgentId
    {
        get { return agentId; }
        set { agentId = this.scrubAgentId(value); } 
    }

    private string scrubAgentId(string value)
    {
        if(value == null)
            return value;
        char[] arr = value.ToCharArray();

        arr = Array.FindAll<char>(arr, (c => (char.IsLetterOrDigit(c))));
        return new string(arr);
    }

answered Apr 26, 2013 at 17:50

Jordan Kaye

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Comments

bash.d · Accepted Answer · 2013-04-26 17:51:32Z

0

In the set part of the property you have an implicit object, value which holds the value you want to set... Use this value as your base

private string agentId;
public string AgentId
{
    get { return agentId; }
    set { agentId = value; } // manipulate value here using your method
}

answered Apr 26, 2013 at 17:51

bash.d

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Comments

bash.d · Accepted Answer · 2013-04-26 17:52:38Z

0

Are you initialising agentid anywhere first?

Its failing on char[] arr = this.AgentId.ToCharArray();

edited Apr 26, 2013 at 17:52

bash.d

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answered Apr 26, 2013 at 17:51

Kyle

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Comments

Nicholas Carey · Accepted Answer · 2013-04-26 17:54:09Z

0

You never reference the value in your setter. You want to do something like this:

private string agentId;
public string AgentId
{
    get
    {
      return agentId ;
    }
    set
    {
      agentId = new string( value.ToCharArray().Where( c => c.IsLetterOrDigit(c) ) ) ;
    }
}

answered Apr 26, 2013 at 17:54

Nicholas Carey

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2 Comments

Jordan Kaye Over a year ago

This will throw an exception if a caller attempts to set AgentId=null;

Nicholas Carey Over a year ago

Obviously. You might notice the 'something like this' qualification. How to handle the edge case there should be pretty obvious (and dependent on the desired semantics of the property).

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