CODEWITHSUNDEEP
c#nullpointerexception
Ryan
Ryan

Reputation: 5546

why does this raise a null object exception

I get a Object reference not set to an instance of an object.:OperatorAssembly: 0 line 157. I don't understand what could trigger this exception

LogFile.Info("order="+order.Id);

if (order.Location != null)
{
    LogFile.Info("order=" + order.Location.Address);
}    
else
{
    LogFile.Info("order location is null");
}

LogFile.Info("order=" + order.Location.Latitude);
LogFile.Info("order=" +  order.IsResolved);
LogFile.Info("order user id=" + order.User.Id);
LogFile.Info("order ser name=" + order.User.Name);
LogFile.Info("order ser dest =" + order.Destination.Address);                       

line 157:
result = new OrderDataDriver
{
    OrderId = order.Id,
    Address = order.Location.Address,
    Lat = order.Location.Latitude,
    Lng = order.Location.Longitude,
    DestinationAddress = order.Destination.Address,
    DestinationLat = order.Destination.Latitude,
    DestinationLng = order.Destination.Longitude,
    IsCanceled = order.IsCanceled,
    IsPendingResponse = order.IsPendingResponse,
    IsResolved = order.IsResolved,
    UserId = order.User.Id,
    Message = order.MessageForDriver,
    UserName = order.User.Name,
    // IsAdvanceBooking = order.AdvenceBookingTime != null,
    AdvanceBookingTime = order.AdvenceBookingTime,
    AdvancePrice = order.CalculatedPrice,
    AdvanceDistance = order.CalculatedDistance,
    SecondsToRespond = 30,
    Status=order.DriverStatus
};

[DataContract]
public class OrderDataDriver
{

    [DataMember] public string Address { get; set; }
    [DataMember] public string Feedback { get; set; }
    [DataMember] public double Lat { get; set; }
    [DataMember] public double Lng { get; set; }
    [DataMember] public int UserId { get; set; }
    [DataMember] public string Status { get; set; }
    [DataMember] public bool? IsEligible { get; set; }
    [DataMember] public bool? IsCanceled { get; set; }
    [DataMember] public bool? IsResolved { get; set; }
    [DataMember] public bool? IsPendingResponse { get; set; }
    [DataMember] public bool? AllowsTracking { get; set; }
    [DataMember]
    public int OrderId { get; set; }
    [DataMember]


    public int App { get; set; }
    [DataMember]
    public int? PreferedDriver { get; set; }
    [DataMember]
    public bool IsAdvanceBooking { get; set; }
    [DataMember]
    public DateTime? AdvanceBookingTime { get; set; }
    [DataMember]
    public double? AdvancePrice { get; set; }
    [DataMember]
    public double? AdvanceDistance { get; set; }
    [DataMember]
    public string DestinationAddress { get; set; }
    [DataMember]
    public double DestinationLat { get; set; }
    [DataMember]
    public double DestinationLng { get; set; }
    [DataMember]
    public string Message { get; set; }
    [DataMember]
    public string UserName { get; set; }
    [DataMember]
    public int SecondsToRespond { get; set; }
}

Upvotes: 2

Views: 127

Answers (4)

Jeppe Stig Nielsen
Jeppe Stig Nielsen

Reputation: 61952

When you use an object initializer, like

result = new OrderDataDriver { OrderId = order.Id, Address = order.Location.Address, Lat = order.Location.Latitude, Lng = order.Location.Longitude, };

don't expect the line number (and column number if you have that) to point out exactly which of the "property assignments" inside the braces { } leads to an exception. After all this is translated to assignments to properties of a temporary (invisible) variable. Only if all goes well, the temporary variable is copied to your result value.

I have also experienced this inconvenience with the stack trace involving object initializers.

Upvotes: 0

Ben Voigt
Ben Voigt

Reputation: 283664

Since things that could be null have already been logged, they should have been caught earlier.

Unless you have a property getter with side effects. Those are pure evil, so watch out. Another possibility is that another thread changed a value. That's even harder to prove.

Upvotes: 0

Jahan Zinedine
Jahan Zinedine

Reputation: 14874

change the complex object initialization to something like this: 

var result = new OrderDataDriver();
result.blablah = foor.bar;

Then you will get a better error message which contains the exact line number which you tried to access a property of a null object.

Here is a good place to refere to this lovely pattern which makes the life of developers easier http://en.wikipedia.org/wiki/Fail-fast

Upvotes: 4

Josh
Josh

Reputation: 44906

Any one of these accessors could blow up if the property is null:

//If Location is null BOOM!!!
Lat = order.Location.Latitude,
Lng = order.Location.Longitude,

//If Destination is null BOOM!!!
DestinationAddress = order.Destination.Address,
DestinationLat = order.Destination.Latitude,
DestinationLng = order.Destination.Longitude,

Upvotes: 0

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