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[英].ToString() does not raise an exception on double? or long? while it will raise an exception on null string
[英]why does this raise a null object exception
我收到未设置为对象实例的Object引用。:OperatorAssembly:0行157。我不明白是什么触发了此异常
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; }
}
将复杂对象初始化更改为以下形式:
var result = new OrderDataDriver();
result.blablah = foor.bar;
然后,您将获得更好的错误消息,其中包含您尝试访问null对象的属性的确切行号。
这里是参考这种可爱模式的好地方,它使开发人员的生活更轻松http://en.wikipedia.org/wiki/Fail-fast
如果该属性为null,则这些访问器中的任何一个都可能崩溃:
//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,
由于可能已经为null
已经被记录,因此应该早些捕获它们。
除非您有带有副作用的吸气剂。 那些纯属邪恶,所以要当心。 另一种可能性是另一个线程更改了一个值。 这甚至更难以证明。
当您使用对象初始化程序时,例如
result = new OrderDataDriver { OrderId = order.Id, Address = order.Location.Address, Lat = order.Location.Latitude, Lng = order.Location.Longitude, };
不要期望行号(如果有的话,还有列号)会准确指出括号{ }
哪个“属性分配”会导致异常。 毕竟,这将转换为对临时(不可见)变量的属性的分配。 只有一切顺利,临时变量才会复制到您的result
值中。
我还经历了涉及对象初始化程序的堆栈跟踪带来的不便。
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