CODEWITHSUNDEEP
c#listcollections
webworm
webworm

Reputation: 11019

Collection field is null when instantiating instance of the class

I have a created an object that will hold errors encountered as well as a boolean field to indicate if any errors were present at all. The class looks like this.

public class ValidationResult
{
    public bool IsValid{ get; set; }
    public List<string> Errors { get; set; }
}

I go to use an instance of this class in a validation method as such

public class ValidationService
{
    // This instance will hold the errors if there are any
    ValidationResult myValidationResult = new ValidationResult();

    public void ValidationMethod()
    {
       // Validation takes place here
       ...
       // Some errors occurred to lets add then to the instance of the ValidationResult object
       myValidationResult.IsValid = false;
       myValidationResult.Errors.Add("An error occurred here are the details");
    }
}

The problem is that the Errors collection in the instance myValidationResult is null? Why is this? I created an instance of the class and the boolean property IsValid is available, yet the Errors collection is null.

Upvotes: 0

Views: 46

Answers (2)

JuanR
JuanR

Reputation: 7803

You must initialize your Errors property:

public class ValidationResult
{
     public ValidationResult()
     {
          Errors = new List<string>();
     }

    public bool IsValid{ get { return (Errors.Count() == 0); } }
    public List<string> Errors { get; set; }
}

Upvotes: 3

Maksim Simkin
Maksim Simkin

Reputation: 9679

Only value types are initialized per default. Your List<string> is a reference type and it does have it default value - null.

Look here for a little bit more information:

https://msdn.microsoft.com/en-us/library/aa691171(v=vs.71).aspx

Upvotes: 2

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