Wednesday, February 17, 2010

Ignore NullReferenceException when reading object properties

Is there any way to direct C# to ignore NullReferenceException (or any specific exception for that matter) for a set of statements?
This is useful when trying to read properties from a deserialized object that may contain many null objects in it.
Having a helper method to check for null could be one way but I’m looking for something close to ‘On Error Resume Next’ (from VB) at a block of statement level.

Try-Catch will skip the succeeding statements on exception

try
{
stmt 1;// NullReferenceException here, will jump to catch - skipping stmt2 and stmt 3
stmt 2;
stmt 3;
}
catch (NullReferenceException) { }
For Example: I’m deserializing an XML message to an object and then try to access a property like

Message.instance[0].prop1.prop2.ID
now prop2 could be a null object (because it doesn’t exists in XML Message – an optional element in XSD). right now I need to check for null for each element in the hierarchy before accessing the leaf element. i.e I’ve to check if instance[0], prop1, prop2 are not null, before accessing ‘ID’.

any better way that avoids null-checking for each element in the hierarchy?

now I’m using delegate and NullReferenceException handling

public delegate string SD();//declare before class definition

string X = GetValue(() => Message.instance[0].prop1.prop2.ID); //usage

//GetValue defintion
private string GetValue(SD d){
try
{
return d();
}
catch (NullReferenceException) {
return "";
}

}

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