Question

I run the following code snippet.

Public Shared Sub DisplayDnsConfiguration() 
Dim adapters As NetworkInterface() = NetworkInterface.GetAllNetworkInterfaces()
Dim adapter As NetworkInterface
For Each adapter In  adapters
    Dim properties As IPInterfaceProperties = adapter.GetIPProperties()
    Console.WriteLine(adapter.Description)
    Console.WriteLine("  DNS suffix................................. :{0}", properties.DnsSuffix)
    Console.WriteLine("  DNS enabled ............................. : {0}", properties.IsDnsEnabled)
    Console.WriteLine("  Dynamically configured DNS .............. : {0}", properties.IsDynamicDnsEnabled)
Next adapter

End Sub 'DisplayDnsConfiguration

I understand the end result, some properties are printed. However I don’t understand the way there.

The following three lines are the ones I don’t understand:

1. Dim adapters As NetworkInterface() = NetworkInterface.GetAllNetworkInterfaces()
2. Dim adapter As NetworkInterface
3. For Each adapter In  adapters

Regarding line 1, why is the As NetworkInterface(), I understand when it is string or integer etc.. but not NetworkInterface(). Then I assume it populate the “adapters” with the data returned from the GetAllNetworkInterfaces() method.

Regarding 2. Same as above, but why doesn’t it use () in the end?

Regarding 3. Why use the adapter In adapters? What does it actually do? I understand it loops through the interfaces, but how?

Thanks

Answer 1

Dim yourIndividualName as SomeType

declares a variable called yourIndividualName which type is SomeType. int and String are rather primitive types compared to a NetworkInterface, but declaring them is the same.

For example:

Dim someText as String

To declare an array (a list) simply add () to the type

Dim severalTexts as String()

Back to your question:

1:

Dim adapters As NetworkInterface()

Declares a list (actually an array) of NetworkInterface called adapters, but the list is empty. Then = NetworkInterface.GetAllNetworkInterfaces() fills that list.

2:

Dim adapter As NetworkInterface

This declares one empty variable of type NetworkInterface. It is later used to go through the list.

3:

For Each adapter In adapters
    ' do some stuff
Next adapter

This takes the first element in the list adapters, saves it in adapter and does the stuff between For and Next. When there is another item in the list, For takes the next one, saves it in adapter and so on, until it reached the end of the list adapters. Between For and Next you can use adapter to e.g. display some of its properties etc.

A shorter version that does the same:

For Each adapter as NetworkInterface In NetworkInterface.GetAllNetworkInterfaces()
    Dim properties As IPInterfaceProperties = adapter.GetIPProperties()
    Console.WriteLine(adapter.Description)
    Console.WriteLine("  DNS suffix................................. :{0}", properties.DnsSuffix)
    Console.WriteLine("  DNS enabled ............................. : {0}", properties.IsDnsEnabled)
    Console.WriteLine("  Dynamically configured DNS .............. : {0}", properties.IsDynamicDnsEnabled)
Next adapter