PRB:Unexpected Results When Raise Method Propogates OLE Errors (129941)
The information in this article applies to:
- Microsoft Visual Basic Standard Edition, 32-bit, for Windows 4.0
- Microsoft Visual Basic Professional Edition, 16-bit, for Windows 4.0
- Microsoft Visual Basic Professional Edition, 32-bit, for Windows 4.0
- Microsoft Visual Basic Enterprise Edition, 16-bit, for Windows 4.0
- Microsoft Visual Basic Enterprise Edition, 32-bit, for Windows 4.0
This article was previously published under Q129941 SYMPTOMS
When creating OLE Servers, you often need to propagate errors specific to
the OLE Server back to the client application by using the Raise method.
The valid range of Error numbers is 0 - 65535, including those defined by
Visual Basic. While there is a constant (vbObjectError) from which all OLE
Server errors can start, unexpected results can occur when errors are
raised between vbObjectError and vbObjectError + 512.
CAUSE
Visual Basic remaps some error messages between vbObjectError and
vbObjectError + 512 to standard run-time errors, which can result in
unexpected behavior if user-defined error numbers are not greater then
vbObjectError + 512.
Because some error numbers are re-mapped by Visual Basic to standard OLE
Automation run-time errors, error trapping code that relies on values
between vbObjectError and vbObjectError + 512 are never be executed.
RESOLUTION
Below is sample OLE Server that correctly uses the Raise method to generate
a user-defined error > vbObjectError + 512.
Step-by-Step Example- Start a new project in Visual Basic. Form1 is created by default.
- Add a command button (Command1) to Form1.
- Add the following code to the Command1_Click procedure:
Sub Command1_Click()
On Error GoTo errhand
Dim clsClass1 As New Class1
clsClass1.Prop1 = -4 ' Set property to invalid value
Exit Sub
errhand:
If Err.Number > vbObjectError Then
MsgBox prompt:="User Defined OLE Automation Error (" & _
CStr(Err.Number - vbObjectError) & "):" & _
Chr$(13) & Chr$(10) & Err.Description, _
Buttons:=vbExclamation, Title:=Err.Source
Else
MsgBox prompt:=Err.Description, Buttons:=vbExclamation
End If
End Sub
- Insert a Class Module by choosing Class Module from the Insert Menu
(ALT, I, C). Class1 is assigned to the Name property by default.
- Add the following code to the Class1:
Property Let Prop1(vntValue)
If vntValue < 0 Then
' Note the Error Number is > the vbObjectError + 512
Err.Raise Number:=vbObjectError + 1000, Source:="Class1", _
Description:="Invalid Property Value (Valid Values are 0 - 65535)"
' Note "Invalid Property Value (Valid Values are 0 - 65535)" is a
' custom error message
End If
End Property
- Change the Error Trapping option to Break on Unhandled Errors by
choosing Options form the Tools menu and selecting the Advanced Tab.
This allows the error to be trapped in code, instead of the debuger
stopping on the Raise Method within the Property Procedure in Class1.
- Press the F5 key to run the program.
- Click the Command1 button. A Message Box appears indicating a
user-defined OLE Automation error has occured.
Modification Type: | Major | Last Reviewed: | 12/9/2003 |
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Keywords: | kbprb KB129941 |
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