空值检查

Question

i have one issue

attrval[5] = WrmService.WindowsAgent.AgentVersion;

From above if attrval[5] is null or not getting any value or any strings other than numeric values i want to assign attrval[5] to value '0.0.0.0' otherwise i will display the numeric value which is coming.What coding i have to implement here

and finally at UI there are two possible chances one is value is 0.0.0.0 or numeric value. if it is 0.0.0.0 i will display 'Unknown' string from resource file or i will display the numeric value in LISTVIEW

i am doing that one like shown below

if(Data.AgentVersion ==null)
                         SubItems.Add(ResourcePolicySystemsLVI.m_nullVersion);
 else
                     SubItems.Add(((IResourcePolicy)Data).AgentVersion);

Is this sufficient means Is 0.0.0.0 is equal to null or i want to change if(Data.AgentVersion ==null) to if(Data.AgentVersion ==0.0.0.0)

Answer 1

Comparison with null and comparison with a certain value which represents no value are not the same thing. If that's all you're asking, then you have to check for both separately.

However I don't know enough about the WrmService to say if a null value is ever possible.

Answer 2

To answer your basic question 0.0.0.0 is not equivalent to null .

Your test should be:

if (Data.AgentVersion == null || Data.AgentVersion.Equals("0.0.0.0")

assuming Data.AgentVersion is a string.

You might want to implement something along the same lines as String.IsNullOrEmpty which you can call where ever you need to do this test.

Answer 3

You could try this to check for a null or a number:

attrval[5] = (WrmService.WindowsAgent.AgentVersion == null || Microsoft.VisualBasic.Information.IsNumeric(WrmService.WindowsAgent.AgentVersion)) ? "0.0.0.0" : WrmService.WindowsAgent.AgentVersion;

Or if its just a null check you could try this:

attrval[5] = WrmService.WindowsAgent.AgentVersion ?? "0.0.0.0";