error "Unable to cast object of type 'System.Int32' to type 'System.Collections.Generic.List`1[System.Int32]'"

Question

I have an package delivery application and I am getting an error in my code below:

public class DeliveryDriver
{
    public List<int> DriverID { get; set; }
    public List<string> DriverName { get; set; }
}

var IDeliveryDriver = new List<DeliveryDriver>();

foreach (DataRow dr in dsDriverID.Tables[0].Rows)
{
    IDeliveryDriver.Add(new DeliveryDriver
    {
        DriverID = (List<int>)dr["DriverId"],
        DriverName = (List<string>)dr["DriverName"]
    });
}

The error occurs at the IDeliveryDriver.Add line and it goes into a catch block. The error is:

Unable to cast object of type 'System.Int32' to type 'System.Collections.Generic.List`1[System.Int32]'

What is causing the error?

Solution

The error message says it all - the DriverId field in each row is an int, not a List<int>. Ditto for DriverName being a string, not a List<string>. You should change your DriverId and DriverName properties to be int and string respectively, then cast to the right type too:

public class DeliveryDriver
{
    public int DriverID { get; set; }
    public string DriverName { get; set; }
}

...

foreach (DataRow dr in dsDriverID.Tables[0].Rows)
{
    IDeliveryDriver.Add(new DeliveryDriver
    {
        DriverID = (int) dr["DriverId"],
        DriverName = (string) dr["DriverName"]
    });
}

After all, each delivery driver does only have one name and one ID, don't they?