检查元素中是否存在特定属性

Question

i need to check if a specific Attributes ConnectionInd exists in the Element of FlightSegment . If it exist, i will store the value, if it doesnt, i will move on and read the next attributes.

The following is if it exist:

<FlightSegment ArrivalDateTime="06-16T06:10" ConnectionInd="O" DepartureDateTime="2013-06-16T00:15" SmokingAllowed="false" eTicket="true">
     <Destination ... />
</FlightSegment>

And this is if it doesn't exist:

<FlightSegment ArrivalDateTime="03-27T17:35" DepartureDateTime="2013-03-27T13:30" SmokingAllowed="false" eTicket="true">
     <Destination ... />
</FlightSegment>

i'm checking it with the following code but when there's no ConnectionInd , it will throw an error saying Object reference not set to an instance of an object.

if (FlightSegment.Item(f).Attributes["ConnectionInd"].Value != "" && FlightSegment.Item(f).Attributes["ConnectionInd"] != null)
{
    string conInd = FlightSegment.Item(f).Attributes["ConnectionInd"].Value;
}

Answer 1

Vice versa:

First check

FlightSegment.Item(f).Attributes["ConnectionInd"] != null

then

FlightSegment.Item(f).Attributes["ConnectionInd"].Value != ""

Otherwise if it's indeed null, you will get NullReferenceException which you're actually getting.

---

More efficient:

var att = FlightSegment.Item(f).Attributes["ConnectionInd"];
if (var != null)
{
    string cind = att.Value;
}

Answer 2

应该有一个像hasAttribute之类的方法或类似的方法，而不是FlightSegment.Item（f）.Attributes [“ ConnectionInd”]。Value，因为如果“ ConnectionInd”不存在，您将试图获取“ Value”空对象的值，这将导致异常。