Lenze VisiWinNet VisiWinNET Smart - Handbuch (Seite 257)

Appendix
Scripts
Troubleshooting within functions
6
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257 SHP−VWNS DE/EN 6.1
6.4.2 Troubleshooting within functions
Generally two types of errors are distinguished:
ƒ Syntactic errors
ƒ Runtime errors
Syntactic errors
Syntactic errors or missing variable declarations are already reported during the creation
of the project. Detecting and eliminating these errors is relatively uncomplicated for the
developer, since they are already reported during the development stage. Programming
errors in the project are shown during the creation (via the menu item Project
® Creation"
or the shortcut Ctrl+Shift+B)in the output window. If the project contains errors that are
detected by the compiler, it cannot be started.
Runtime errors
Runtime errors such as "Division By Zero" or missing object references are only detected
when the corresponding function is executed. The risk with this is that after
commissioning the code is supplied with data from the process which have not been
checked and result in an exception. Here it helps to use the Try−Catch condition with a
defined response for the case of error.
Private Sub ItemServer1_Change(ByVal sender As System.Object, _
ByVal e As VisiWinNET.DataAccess.ChangeEventArgs) Handles ItemServer1.Change
Try
Dim Divident As Double = _
VisiWinNET.Services.AppService.VWGet("Ch1.myDivident")
Dim Divisor As Double = e.Value
Dim Quotient As Double = Divident / Divisor
VisiWinNET.Services.AppService.VWSet("Ch1.myQuotient", Quotient)
Catch ex As Exception ’ooh, an error
If MsgBox("ItemServer1_Change results in: " _
& vbCrLf & ex.Message _
& vbCrLf & "Continue?", _
MsgBoxStyle.YesNo) = MsgBoxResult.No Then
’decision: End application
VisiWinNET.Forms.ProjectForms.StartForm.ShutdownProject()
End If
End Try
End Sub
Example: If a runtime error during the calculation "dividend/divisor= quotient" occurs, the
program run skips to the Catch condition. By means of a message box it is now decided
whether the application is to be closed.