ArcGIS Engine Developer Guide

THE V ISUAL BASIC 6 DEVELOPMENT ENVIRONMENT
debugger DLL belongs to the component category, and it doesn’t. What this
means is that anytime a component category is used to automate the loading of a
DLL, the DLL cannot be debugged using the Visual Basic debugger.
This causes problems for many of the ways to extend the framework. The most
common way to extend the framework is to add a command or tool. Previously,
it was discussed how component categories were used in this instance. Remember
that the component category was only used to build the list of commands in the
dialog box. This means that if the command to be debugged is already present on
a toolbar, the Visual Basic debugger can be used. Hence, the procedure for debugging
Visual Basic objects that implement the ICommand interface is to ensure that
the command is added to a toolbar when ArcMap is executed standalone and,
after saving the document, load ArcMap through the debugger.
In some cases, such as extensions and property pages, it is not possible to use the
Visual Basic debugger. If you have access to the Visual C++ debugger, you can
use one of the options outlined below. Fortunately, there are a number of ESRI
Visual Basic Add-ins that make it possible to track down the problem quickly and
effectively. The add-ins, described in ArcGIS Developer Help in the section
‘Visual Basic Developer Add-Ins’, provide error log information including line
and module details. A sample output from an error log is given below; note the
call stack information along with line numbers.
Error Log saved on : 8/28/2000 - 10:39:04 AM
Record Call Stack Sequence - Bottom line is error line.
chkVisible_MouseUp C:\Source\MapControl\Commands\frmLayer.frm Line : 196
RefreshMap C:\Source\MapControl\Commands\frmLayer.frm Line : 20
Description
Object variable or With block variable not set
Alternatives to the Visual Basic debugger
If the Visual Basic debugger and add-ins do not provide enough information, the
Visual C++ debugger can be used, either on its own or with C++ ATL wrapper
classes. The Visual C++ debugger does not run the object to be debugged out of
process from ArcMap, which means that none of the above issues apply. Common
debug commands are given in the Visual C++ section ‘Debugging tips in Developer
Studio’. Both techniques below require the Visual Basic project to be compiled
with debug symbol information.
The Visual C++ debugger can work with this symbolic debug information and
the source files.
Create debug symbol information using the
Create Symbolic Debug Info option on the
Compile tab of the Project Properties dialog box.
Visual C++ debugger
It is possible to use the Visual C++ debugger directly by attaching to a running
process that has the Visual Basic object to be debugged loaded and setting a break
point in the Visual Basic file. When the line of code is reached, the debugger will
halt execution and step into the source file at the correct line. The required steps
are as follows:
1. Start an appropriate application, such as ArcMap.exe.
Chapter 4 • Developer environments • 97