I wrote an error handling summary (VBA), and would like to share with you.
http://automation.youplayoff.com/201...a-testpartner/

You can also read it below, but I believe the above link is more reading friendly. Any comments and suggestions are welcome.

There are 3 error handling statements in Visual Basic of Application (VBA), which can be used in TestPartner. However, these statements can NOT be used in QTP, since QTP uses the Visual Basic Scripting Edition (VBScript) scripting language.

The 3 error handling statements in VBA are:

1, On Error GoTo line
This statement has been used in post#9.
This statement enables the error-handling routine that starts at line specified in the required line argument. The line argument is any line label or line number. If a run-time error occurs, control branches to line, making the error handler active. The specified line must be in the same procedure as the On Error statement; otherwise, a compile-time error occurs.

2, On Error Resume Next
This statement has been used in post#12.
This statement specifies that when a run-time error occurs, control goes to the statement immediately following the statement where the error occurred where execution continues. Use this form rather than On Error GoTo when accessing objects.

3, On Error GoTo 0
This statement has been used in post#12.
This statement disables any enabled error handler in the current procedure (It doesn’t specify line 0 as the start of the error-handling code, even if the procedure contains a line numbered 0.).

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In the script of post#12, there is a line to move the scroll bar inside the TreeView window horizontally: “TreeView(“Parent.Caption=Preferences”).Scroll 0, tpScrollHorizontal”. This line of script is necessary when a protocol name is longer than the TreeView window width.

However, when all the protocols names are shorter than the TreeView window width, then there will be no scroll bar, which is an expected situation, but since the script can not find the scroll bar, it will pop up an error message to stop the script from running.

In order to handle the above situation, I wrote “On Error Resume Next” right above “TreeView(“Parent.Caption=Preferences”).Scroll 0, tpScrollHorizontal” line. In this way, if there is a scroll bar, then the script will scroll the scroll bar horizontally to position x=0, and if there is no scroll bar, then the script will skip the scroll step, and run the next step.

Everything looks perfect until I found out this: even though the “On Error Resume Next” is right above “TreeView(“Parent.Caption=Preferences”).Scroll 0, tpScrollHorizontal” line, it does NOT only affect the “TreeView(“Parent.Caption=Preferences”).Scroll 0, tpScrollHorizontal” line, it will affect all the lines after “On Error Resume Next”, which means, if there is an error happens after “On Error Resume Next” is executed, then the error will be ignored anyway.

If LOOP is used, when an error happens at a line above “On Error Resume Next”, the error could still be ignored, as long as the error doesn’t happen at the first iteration of the loop and before “On Error Resume Next” is executed. See the example below from post#12:
view source
print?
1.For i = 1 to Imax
2. ...
3. TreeView("Parent.Caption=Preferences").SelectItem (ProtocolPath)
4. ...
5. On Error Resume Next
6. TreeView("Parent.Caption=Preferences").Scroll 0, tpScrollHorizontal
7. ...
8.Next

Real/unexpected error may happen at line “TreeView(“Parent.Caption=Preferences”).SelectItem (ProtocolPath)”, and the script needs to alert me about these errors, but since the existence of “On Error Resume Next”, most errors happen at “TreeView(“Parent.Caption=Preferences”).SelectItem (ProtocolPath)” will be ignored, unless it happens when i=1, i.e., when “On Error Resume Next” haven’t been reached.

How to solve this issue? It is simple, you just need to add the “On Error GoTo 0″ line right above “TreeView(“Parent.Caption=Preferences”).SelectItem (ProtocolPath)”. The script will looks like this:
view source
print?
01.For i = 1 to Imax
02. ...
03. On Error GoTo 0
04. TreeView("Parent.Caption=Preferences").SelectItem (ProtocolPath)
05. ...
06. On Error Resume Next
07. TreeView("Parent.Caption=Preferences").Scroll 0, tpScrollHorizontal
08. ...
09.Next

In conclusion, to ignore expected error, use “On Error Resume Next”; to alert unexpected error, use “On Error GoTo 0″ if “On Error Resume Next” has been used in the script (same level). web page