I've started using try-catch blocks (a bit late, I know!), but now I'm not sure what to do with the exception once I've caught it. What should I do?
Try
connection.Open()
Dim sqlCmd As New SqlCommand("do some SQL", connection)
Dim sqlDa As New SqlDataAdapter(sqlCmd)
sqlDa.Fill(dt)
Catch ex As SQLException
' Ahhhh, what to do now!!!?
Finally
connection.Close()
End Try
Unless you were expecting the error (the API says it can occurr) and can handle it (there is an obvious step to take if the exception occurrs), you probably want to crash with a lot of noise. This should happen during testing / debugging, so that the bug can get fixed before the user sees it!
Of course, as commenters have pointed out, the user should never really see all this noise. A high-level try/catch or some other method (EMLAH, I hear for .net web projects) can be used to show the user a nice error message ("Oops! Something went wrong! What on earth were you trying to do?") with a submit button...
So basically, my point is this: Do not catch errors you don't know how to handle! (except for the high-level handler). Crash early and with as much information as possible. This means you should log the call stack and other vital information if at all possible for debugging.
It depends entirely on context. Possible options include "Use default data instead of data from the database" and "Display an error message to the user".