Documentation/DevGuide/ProUNO/Basic/Exception Handling

OpenOffice.org Developer's Guide

Professional UNO

< Previous Section

Next Section >

• Introduction
• API Concepts

• Data Types

• Simple Types
• The Any Type
• Interfaces
• Services
• Structs
• Predefined Values
• Sequences
• Modules
• Exceptions
• Singletons

• Understanding the API Reference

• UNO Concepts

• UNO Interprocess Connections

• Starting OpenOffice.org in Listening Mode
• Importing a UNO Object
• Characteristics of the Interprocess Bridge
• Opening a Connection
• Creating the Bridge
• Closing a Connection
• Example: A Connection Aware Client

• Service Manager and Component Context

• Service Manager
• Component Context

• Using UNO Interfaces
• Properties
• Collections and Containers
• Event Model
• Exception Handling
• Lifetime of UNO objects

• acquire() and release()
• The XComponent Interface
• Children of the XEventListener Interface
• Weak Objects and References
• Differences Between the Lifetime of C++ and Java Objects

• Object Identity

• UNO Language Bindings

• Java Language Binding

• Getting a Service Manager
• Transparent Use of Office UNO Components
• Handling Interfaces
• Type Mappings

• Mapping of Sequence Types
• Mapping of Enum Types
• Mapping of Struct Types
• Mapping of Exception Types
• Mapping of Interface Types
• Mapping of UNOIDL
• Mapping of Services
• Mapping of Singletons
• Inexact approximation of UNO Value Semantics

• C++ Language Binding

• Establishing Interprocess Connections
• Transparent Use of Office UNO Components
• Type Mappings

• Mapping of Struct Types
• Mapping of Interface Types
• Mapping of Sequence Types
• Mapping of Services
• Mapping of Singletons

• Using Weak References
• Exception Handling in C++

• OpenOffice.org Basic

• Handling UNO Objects

• Instantiating UNO Services
• Getting Information about UNO Objects

• Mapping of UNO and Basic Types

• Mapping of Simple Types
• Mapping of Sequences and Arrays
• Mapping of Structs
• Mapping of Enums and Constant Groups

• Case Sensitivity
• Exception Handling
• Listeners

• Automation Bridge

• The Service Manager Component
• Using UNO from Automation

• Calling Functions and Accessing Properties
• Return Values
• Usage of Types

• Using Automation Objects from UNO
• Type Mappings

• Default Mappings

• Mapping of Simple Types
• Mapping of Hyper and Decimal
• Mapping of String
• Mapping of Interfaces and Structures
• Mapping of Sequence
• Mapping of Type

• Conversion Mappings
• Client-Side Conversions
• Value Objects
• Exceptions and Errorcodes

• Automation Objects with UNO Interfaces
• DCOM
• The Bridge Services
• Unsupported COM Features

• CLI Language Binding

• The Language Binding DLLs
• Type Mapping

• Type Name Decoration
• Type Mappings
• Additional Structures

• Lifetime Management and Obtaining Interfaces
• Writing Client Programs

• The Override Problem
• Important Interfaces and Implementations

< Previous Page

Next Page >

Unlike UNO, Basic does not support exceptions. All exceptions thrown by UNO are caught by the Basic runtime system and transformed to a Basic error. Executing the following code results in a Basic error that interrupts the code execution and displays an error message:

 Sub Main
     Dim oLib
     oLib = BasicLibraries.getByName( "InvalidLibraryName" )
 End Sub

The BasicLibraries object used in the example contains all the available Basic libraries in a running office instance. The Basic libraries contained in BasicLibraries is accessed using com.sun.star.container.XNameAccess. An exception was provoked by trying to obtain a non-existing library. The BasicLibraries object is explained in more detail in Advanced Library Organization.

The call to getByName() results in this error box:

Unhandled UNO Exception

However, the Basic runtime system is not always able to recognize the Exception type. Sometimes only the exception message can be displayed that has to be provided by the object implementation.

Exceptions transformed to Basic errors can be handled just like any Basic error using the On Error GoTo command:

 Sub Main
     On Error Goto ErrorHandler ' Enables error handling
     
     Dim oLib
     oLib = BasicLibraries.getByName( "InvalidLibraryName" )
     MsgBox "After the Error"
     Exit Sub
   
 ' Label
 ErrorHandler:
     MsgBox "Error code: " + Err + Chr$(13) + Error$
     Resume Next ' Continues execution at the command following the error command
 End Sub

When the exception occurs, the execution continues at the ErrorHandler label. In the error handler, some properties are used to get information about the error. The Err is the error code that is 1 for UNO exceptions. The Error$ contains the text of the error message. Executing the program results in the following output:

Handled UNO Exception

Another message box "After the Error" is displayed after the above dialog box, because Resume Next goes to the code line below the line where the exception was thrown. The Exit Sub command is required so that the error handler code would be executed again.

Content on this page is licensed under the Public Documentation License (PDL).