Events
Err.Clear
Err.Raise
Required properties
Err.Number
Optional properties
Err.Description
Err.HelpContext
Err.HelpFile
Err.LastDllError
Err.Source
About the event properties
Err.Clear
is called solely to clear the most recent error from the
error structure. In the event you fail to clear the error, it would persist and
be called again, especially in longer functions where you may resume the function
at an earlier point than simply to exit the functions or sub running. Failing
to clear the event would also cause the error to persist cross modules if occurring
in a function of the public or global scope.
Err.Raise
is called to force an error of the specified, optional
properties to occur. Thereby you can call up the reference to an error at run
time to generate a list of all errors, display a specific help context ID or
help file for specific errors to the user.
It is also an event that we will use in the definition of our own errors later on in this article.
The required properties
There is only one required property in the error object model. Namely, the Err.Number. In order to find all data and information pertaining to a specific error events properties, this number is the "ID" number for the event it self, allowing you to call back the more detailed information about the error. Provided of course that such information exists and has been programmatically included in the compiled files or classes called by your application.
The optional properties
Err.Description
is a string expression describing the error raised.
If the description is omitted, the Visual Basic runtime module will attempt to
localize a correlating description based on the
Err.Number
. Once
again remember that if you define your own error number and it clashes with an
existing one, this may be cause for some concern if your user is not provided
a description correlating with your error number. If the Visual Basic runtime
module is unable to locate such a description, it will simply generate a standard
output saying "Application-defined or object-defined error". Rather
empty, and meaningless to your end user.
Err.HelpContext
is an identifier to a help context ID in a provided
help file for your application. Once more, if omitted, the VB runtime will attempt
to establish a link to the existing Visual Basic Help file based on the error
number value, if it exists. The best thing to do is to define this value to 0
not to confuse your users, when no help file has been provided for your application.
Err.HelpFile
is the fully qualified path to an MS Windows *.hlp
file used by your application. If omitted the application will attempt to use
the fully qualified drive, path, and file name of the Visual Basic Help file,
if existing on the end users machine.
Err.Source
is a string expression displaying the name of the object
or application that generated the error raised. If you should set this programmatic
ID your self, use the form project.class. If you do not specify the source, it
is automatically generated for you in form of the name of the current project.
This is displayed at design time in the menu under the menu option; Project >>
Project Properties >> General >> Project Name.
Err.LastDllError
is only returned or generated by call to a dynamic-link
library (DLL). This property is read-only and will only return the error code
number. Study the Visual Basic help file further for details on how to obtain
DLL error codes, and study the DLL providers documentation closer to find the
relevant meaning to each error code and how to handle the error codes passed
form DLL files.
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