INFO: Overview of Debugging VBCE Applications

This article describes some of the resources available for debugging applications created with the Microsoft Windows CE Toolkit for Visual Basic (VBCE).

A VBCE program is handled differently by the integrated development environment (IDE) than a regular Visual Basic application. VBCE programs are completely compiled into .pvb files before they are handed off to pvb.exe, which actually runs the code in the program. VBCE programs run completely outside of the Visual Basic IDE, so there is no compile on demand as in regular Visual Basic. Only very basic syntax checking is done by the add-in (CEIDE.DLL) when the program is compiled; therefore, some errors will not be caught until run-time.

Debugger

VBCE comes with a separate Debugger utility (VBDBG.EXE) for debugging Windows CE applications. The Debugger runs as a separate program outside of the Visual Basic IDE, therefore some of the debugging options available in the Visual Basic IDE are not supported by the toolkit.

The Debugger includes several useful windows: A Watch Window displays the values of variables or expressions during execution. An Immediate Window allows small code statements to run. A Call Stack shows procedures in execution. An Object window shows the hierarchy of running objects. Objects can be opened to view their code, add breakpoints, etc. Applications are compiled before reaching the debugger, so application code cannot be edited in the debugger's Immediate Window. Because all errors, other than syntax errors, are caught at run-time, applications must be running in either the emulated or remote Windows CE environment before you can begin the debugging process. Though most debugging is done while in emulation mode, you should also debug your application on the remote device in order to ensure your application is error-free.

Breakpoints entered in the Visual Basic IDE will not be recognized in the Debugger, but breakpoints can be added in the Debugger's code window for the object.

Error Trapping

The "On Error Resume Next" statement is useful when performing inline error handling. This statement is the only error handling statement the toolkit currently supports. On Error Resume Next does not clear the Err object, so you can use inline error handling to display a meaningful error messages rather than displaying the generic "Application Error" message.

Although VBCE programs keep running after generating an application error, execution of the current procedure halts unless an On Error Resume Next statement is in the procedure and before where the error occurred.

The Debug object is not supported in VBCE. Alternative strategies could be using the File control to log information about program execution or using MsgBoxes and controls to display program status.

The "On Error GoTo 0" line is included in VBCE to disable inline error handling. If you use this line in code, subsequent errors may cause executing code to stop, although the rest of the application will continue.

Err Object

Run-time errors produce a generic Application Error dialog box with the message: There is no other information about what may have caused the error, and no Help button to retrieve information from the online Help files. When an application error occurs, the Err object is loaded with the error number and a description of the error.

You can check the Err object in your code in various ways, including displaying the error information in a MsgBox, such as: If the error is coming from a control, the Err.Source property can be checked. Usually, the Err object supplies enough information to determine what caused the error. Tracing through a program with the debugger can reveal more information. After code is modified, recompile the .pvb to test your changes. If a program is still running on the device or emulator, it must be closed before trying to run it again from the IDE.

Windows CE Toolkit Help for Visual Basic 6.0