Step 1: Choose a Small Piece of Code
This first step is the most important. The problem of upgrading an application is mostly one of scope. The prospect alone can be daunting! The best place to start is small. Dig into your code; find a piece that's comfortable, maybe a spot where you've already made fixes. The smaller, the betterstarting with a function is better than replacing a whole class. I know, I knowit would be so much easier to attack a whole class or set of functionality, right? But we don't want to take the easy approach; we want to take the repeatable approach. Unless you're very lucky, you'll be working on this upgrade while you're maintaining the old code; small chunks will get you there faster.
"But I've got dependencies!" you cry. "My chosen code won't work without classes x and y!" This is a valid argument, but classes x and y will have their own turns, thank you very much. Use placeholder and dummy data when you're upgrading your snippets. Trust your architecture, get the code done, and worry about dependencies when the necessary pieces are in place.
For this example, I've chosen a small piece of pretty common codea function to map a drive in Visual Basic 6. We're going to upgrade it to C#. Nice and simple. Listing 1 shows the full function.
Listing 1Function to map a drive in Visual Basic 6.
Private Const RESOURCE_CONNECTED As Long = &H1& Private Const RESOURCE_GLOBALNET As Long = &H2& Private Const RESOURCETYPE_DISK As Long = &H1& Private Const RESOURCEDISPLAYTYPE_SHARE& = &H3 Private Const RESOURCEUSAGE_CONNECTABLE As Long = &H1& Private Const CONNECT_UPDATE_PROFILE = &H1 Private Declare Function WNetAddConnection2 Lib "mpr.dll" _ Alias "WNetAddConnection2A" (lpNetResource As NETCONNECT, _ ByVal lpPassword As String, ByVal lpUserName As String, _ ByVal dwFlags As Long) As Long Private Type NETCONNECT dwScope As Long dwType As Long dwDisplayType As Long dwUsage As Long lpLocalName As String lpRemoteName As String lpComment As String lpProvider As String End Type Public Function MapDrive(LocalDrive As String, _ RemoteDrive As String, Optional Username As String, _ Optional Password As String) As Boolean 'Example: 'MapDrive "Q:", "\\RemoteMachine\RemoteDirectory", _ '"MyLoginName", "MyPassword" Dim NetR As NETCONNECT NetR.dwScope = RESOURCE_GLOBALNET NetR.dwType = RESOURCETYPE_DISK NetR.dwDisplayType = RESOURCEDISPLAYTYPE_SHARE NetR.dwUsage = RESOURCEUSAGE_CONNECTABLE NetR.lpLocalName = Left$(LocalDrive, 1) & ":" NetR.lpRemoteName = RemoteDrive MapDrive = (WNetAddConnection2(NetR, Username, Password, _ CONNECT_UPDATE_PROFILE) = 0) If MapDrive = True Then lstScripts.AddItem "Drive " & LocalDrive & " mapped to " & RemoteDrive Else lstScripts.AddItem "Unable to Map " & LocalDrive & " to " & RemoteDrive End If End Function