Question

I have the following code below. Which works great expect I want to allow MaxDemand to be a null value. But since i’m parsing a string it seems to error if I don’t put in some value.

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

Whats the best solution to implement an error handling solution? I tried float.TryParse but can’t get that to work.

Thank you for looking over my issue.

    protected void GridView3_RowUpdating(object sender, GridViewUpdateEventArgs e)
    {
    float Cost = 0.0F; 
    float Consumption = 0.0F;
    int InvoiceID = 0;
    float MaxDemand = 0.0F;
    DateTime ServiceFrom = new DateTime();
    DateTime ServiceTo = new DateTime();

    foreach (string key in e.NewValues.Keys)
        switch (key)
        {
            case "TotalInvoice": Cost = float.Parse(e.NewValues[key].ToString()); 
                                break;
            case "EnergyInvoiceID": InvoiceID = int.Parse(e.NewValues[key].ToString()); 
                                break;
            case "Consumption": Consumption = float.Parse(e.NewValues[key].ToString()); 
                                break;
            case "ServiceFrom": ServiceFrom = DateTime.Parse(e.NewValues[key].ToString());
                                break;
            case "ServiceTo":   ServiceTo = DateTime.Parse(e.NewValues[key].ToString());
                                break;
            case "MaxDemand": MaxDemand = float.Parse(e.NewValues[key].ToString());
                                break;
        }

    UpdateInvoice(InvoiceID, Cost, Consumption, ServiceFrom, ServiceTo, MaxDemand);
    GridView3.EditIndex = -1;
    PopulateAccountHistory();
}

Answer 1

The problem here isn’t in the actual parsing of the float or double value. If that failed it would return a more specific exception. It appears that the problem is one of the returns of e.NewValues[key] is returning null and you are throwing on the call to ToString

It would be best to centralize the null checks at the start of the loop. It would also allow you to remove the repeated calls to e.NewValues[key].

 foreach (string key in e.NewValues.Keys) {
   var value = e.NewValues[key];
   if (value == null) { 
       continue;
   }

   var str = value.ToString();
   switch (key) {
     case "TotalInvoice": 
       Cost = float.Parse(str);
       break;

     ...