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Getting Started With Exception Handling &

Debugging & Help

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Exception

An exception is termed as an abnormal condition encountered by an

application during execution.

Exception handling

Is the process of providing an alternate path to be executed

when the application is unable to execute in the desired way.

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Divides an application into blocks of code that have the probability ofraising an error.

Uses the TryCatchFinally statement. Errors are filtered in the Catch block

Structured exception

Try

..statement that can cause exception..

Catch ex

..code which will execute if respective exception occur..

Finally

..code which will execute regardless exception occurrence ..

End Try

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Unstructured exception

Is done by placing an On Error statement in a block of

code.

Uses the On Error GoTo statement to pass the control to a

specific error handler when an error occurs.

Uses the On Error Resume Next statement to pass control to the

next executable statement when an error occurs. Uses the On Error GoTo 0 to disable an error handler

On Error GoTo Lerr

..statement that can cause exception..

Exit SubLerr:

..code which will execute if respective exception occur..

[Resume Next]

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User-defined exceptions

Can be created by deriving a class from the ApplicationExceptionclass.

Class UserExp

Inherits ApplicationException

Public Function GetErrorMessage() as String

Return Invalid opertaion ..

End Function

End Class

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Debugging

Tracing and rectifying an error is termed as debugging.

In order to assist you in debugging logical and run-time errors,

Visual Basic .NET provides extensive debugging tools. You can

access these tools by using:

Debug toolbar

Debug menu

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Debugging Cont..

In an application, by using the debugging tools, you can:

Start execution

Break execution

Stop execution

Step Into

Step OverStep Out

A B C A, B, C

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Debugging Windows

The following windows are used for debugging an application: Watch window Call Stack window The Output window

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Help Providing

We can create following type helps for an application

Context-sensitive help for an application

Pop-up help

Tool tips for a control

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Help Providing cont..

Context-sensitive help for an application

HTML help displays the help content from an HTML file.

When the user presses the F1 key at run time, the HTML page containing thehelp content is displayed.

By using HTML Help files, you can display online context-sensitive help to auser.

HTML Help Workshop is a tool for creating HTML Help files, which storethe help content in HTML format.

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Help Providing cont..

Pop-up help

Provides help through the Help button, also called the Whats This button,

present in an application to the right of the title bar.

Is most effective in modal dialog boxes.

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Help Providing cont..

Tool tips for a control

Is a brief help message for individual controls on a form.

Can be displayed by adding a ToolTip control to the form and enter thetext in the ToolTipText property of the control for which the tool tip is to

be displayed. The SetToolTip() method of the ToolTip control is used to set the tool tip

text for a control.