"Object reference not set to an instance of an object" on custom Validation

Question

I'm trying to create a custom validation rule which will check to see if Times overlap in any case, to do this I have the following:

public class TimesheetLogicAttribute : ValidationAttribute
{

    public TimesheetLogicAttribute()
    {
        //this.jobRecords = jobRecords;
    }

    protected override ValidationResult IsValid(object value, ValidationContext validationContext)
    {
        var records = value as List<TimesheetJobRec>;

        records = records.OrderBy(r => r.StartTime).ToList();
        DateTime? current = null;

        foreach(var record in records)
        {
            if (record.StartTime > record.FinishTime)
            {
                return new ValidationResult("Finish time is before start time on " + record?.JobNumber);
            }

            if (current == null)
            {
                current = record.FinishTime;
                continue;
            }

            if(record.StartTime < current)
            {
                return new ValidationResult("Time overlapping");
            }
            current = record.FinishTime;
        }

        return ValidationResult.Success;

        //return base.IsValid(value, validationContext);
    }

}

My corresponding model is:

public class TimesheetJobRec : ModelsBase
{
    // Job number stuff needs to go in here.
    [Required]
    public string JobNumber { get; set; }
    public Timesheet Timesheet { get; set; }

    [Required]
    public string WorkDescription { get; set; }

    [Required]
    [DataType(DataType.Time)]
    public DateTime StartTime { get; set; }

    [Required]
    [DataType(DataType.Time)]
    public DateTime FinishTime { get; set; }

    [Required]
    public double LunchTime { get; set; }

    [ReadOnly(true)]
    [Range(0.25, 24)]
    public double Total { get; set; }

}

Then I decorate my view model like this:

  [Display(Name = "Job Records")]
  [TimesheetLogic]
  public IList<TimesheetJobRec> JobRecords { get; set; }

This all works fine and in my validation I receive my item list correctly, the problem occurs when returning a ValidationResult I get the following error on the ASP side of things:

Object reference not set to an instance of an object.

Line 43:                         <th>Total</th>
Line 44:                     </tr>
Line 45:                     @foreach (var item in Model.JobRecords)
Line 46:                     {
Line 47:                         Html.RenderPartial("_JobEditorRow", item);

On Line 45 the error is thrown, in that foreach in my View I am just rendering existing items. I'm not sure what the cause for this is and whether I'm doing validation correctly or not.

Check the value of Model.JobRecords. Most probably the object might be null. — Karthik AMR, Jan 11 '17 at 10:25
@KarthikAMR Yes I was thinking this, but in my Validation attribute how can I return an instance of the viewmodel? AFAIK we can only return a `ValidationResult` in which `null` will be a success; however I need to return my view model which will include the instance of `Model` and `Model.JobRecords`. — sham, Jan 11 '17 at 10:27
You don't return a model in a validation attribute. You return your model in the POST method (using `return View(model);`) if `ModelState` is invalid — , Jan 11 '17 at 10:29
@StephenMuecke I am doing that already in my controller method on the `GET` for that same page so I don't see why this would have an issue. — sham, Jan 11 '17 at 10:36
But you obviously not doing it in the POST method. Your validation attribute has nothing at all to do with your issue. — , Jan 11 '17 at 10:37
@KarthikAMR I am instantiating the object when the `GET` request is made initially to the page, I just want to return an error message onto the same page in this case which doesn't seem to be happening. Maybe I'm not understanding something. — sham, Jan 11 '17 at 10:37

score 0 · Answer 1 · answered Jan 11 '17 at 11:10

You must set the JobRecords property of each instance of the view model that you pass to the view to an IList<TimesheetJobRec>. You can use an auto-property initializer to initialize the property in C#6:

[Display(Name = "Job Records")]
[TimesheetLogic]
public IList<TimesheetJobRec> JobRecords { get; set; } = new List<TimesheetJobRec>();

Or you could do it in the constructor of the view model class

//constructor
public YourViewModel()
{
    JobRecords = new List<TimesheetJobRec>();
}

This will make sure that the property is always initialized provided that you don't explicitly set it to a null reference somewhere.

"Object reference not set to an instance of an object" on custom Validation

1 Answers1