Re: Custom PaperSize Problem - Visual Basic Discussion Boards

Timer for Test Timeout + General Code Structure

RichardBerry4-May-07 22:51

4-May-07 22:51

Hi

1) Can anyone help me with how to structure some code that if something has not happened in a certain time, the function will return 'False'. The example 'Test0' below must be bad because I am constantly sitting in a loop checking the Port Pin.

2) Is there a better way to use a Timer in 'Test1'?

3) Which routines should be at the Top of the code. Since the routine 'DoTests' is the main loop, I have put it at the top - then as the tests are called, so you find the routines further down in the code. It obviously works anyway around, but I have often noticed in other code examples that the main routine is at the bottom of all the code.

4) After the tests are done (Pass or fail, the routine 'DisplayError is called from the 'DoTests' routine. 'Display Error' in turn calls 'DoTests'. In other words they are constantly calling each other. Is this bad?

Any comments on how I can make this code better will be appreciated..

Example:
Private Sub DoTests()
Test0()
If Not Test1() Then
DisplayError(1)
End If
If Not Test2() Then
DisplayError(2)
End If
DisplayError(10) 'All Tests Passed

End Sub

'Loop until Jig Closes (D0 = 0) to start tests
Private Function Test0() As Boolean
Do While LPTPort.GetState(D0) = 1

Loop
Return True
End Function

Private Function Test1() As Boolean
Dim tmrTestTimeout As Windows.Forms.Timer
tmrTestTimeout.Interval = 3000
tmrTestTimeout.Enabled = True
'Wait for LPTPort pin D1 to go low OR timeout
Do While tmrTestTimeout.Enabled
If LPTPort.GetState(D1) = 0 Then
tmrTestTimeout.Enabled = False
Return True
End If
Loop
'Timed out - so Return False
tmrTestTimeout.Enabled = False
Return False
End Function

Private Sub DisplayError(ByVal intErrorCode As Integer)
Select Case (intErrorCode)
Case 1
Me.lblTestStatus.Text = "Test 1 Failed"
Case 2
Me.lblTestStatus.Text = "Test 2 Failed"
Case 10
Me.lblTestStatus.Text = "All Tests Passed"
Case Else
Me.lblTestStatus.Text = "Unknown Error - Test Aborted"
End Select
'Wait for Jig to open (D0 = 0) so last unit tested is removed
Do While LPTPort.GetState(D0) = 1

Loop
DoTests()
End Sub

Re: Timer for Test Timeout + General Code Structure

kubben5-May-07 1:11

kubben

5-May-07 1:11

I think it is a much better idea to have an actual counter in the loop and only wait a max amount of time. It also is a good idea to Application.DoEvents while you are in a loop or your form won't refresh.

dim cnt as Integer = 0
Do While (Your normal check here) AndAlso cnt < 100000
'do your other code here
System.Threading.Thread.Sleep(500)
Application.DoEvents
cnt = cnt + 1
Loop

If cnt >= 100000 Then
'didn't finish the test...
End If

I would suggest that type of code over a timer. That way you know for sure that you will exit the loop and with the application.DoEvents it won't look like your application has died and isn't coming back.

Hope that helps.
Ben

Custom PaperSize Problem

AmirAlilou4-May-07 21:54

AmirAlilou

4-May-07 21:54

Hi
I have a problem with changing printer's paper size to custom paper size(programmatically).
I use PaperSize cunstuctor to create custom paper size and then assign it to PrintDocument.DefaultPageSettings.PaperSize.
this is not change paper size in printer.

Dim pd As PrintDocument = New PrintDocument<br />
Dim pkCustomSize1 As New PaperSize("Custom", 100, 200)<br />
pd.DefaultPageSettings.PaperSize = pkCustomSize1

Please Guide me
Thnaks

Re: Custom PaperSize Problem

Duncan Edwards Jones4-May-07 23:48

Duncan Edwards Jones

4-May-07 23:48

Does the printer support setting custom paper size? Not all do....

(Can't see anything wrong with the code itself)

'--8<------------------------
Ex Datis:
Duncan Jones
Merrion Computing Ltd

Re: Custom PaperSize Problem

AmirAlilou5-May-07 1:05

AmirAlilou

5-May-07 1:05

Thanks for your reply.My printer support custom paper size.it's model is
**HP LaserJet 1020**
but when i programmatically change the printer paper size it dose not affect on printer's paper size.

thanks for your guide.

Re: Custom PaperSize Problem

P P Vilsad6-May-07 5:34

P P Vilsad

6-May-07 5:34

this won't change the printer's pagesize to 100x200 but you will get your printout in the papersize you specified (for that session only).

Vilsad P P
MCTS (Windows Applications) .Net 2.0

Re: Custom PaperSize Problem

AmirAlilou6-May-07 21:15

AmirAlilou

6-May-07 21:15

Hi Vilsad
then i must positioning my text and other objects in page to print correctly?

plese guide me with code snipet
thanks

Re: Custom PaperSize Problem

P P Vilsad7-May-07 3:03

P P Vilsad

7-May-07 3:03

yes you must position your text to the newly set papersize. and it will print correctly
initialise your variables in beginprint event because this will be called first when you call printdocument.print method. set a variable to calculate the current height and check it with the pagesettings.printablearea.height and the current printing hight should not exeed this printarea height. if you have more to print then set the hasmorepages = true or when you need to finish set it to false.
the printpage event is repeatedly called when you set hasmorepages = true
Note: Track your current printing position and it should not exeed the paper's limit, if the limit crossed then you will get a infinite number of pages printed.

Vilsad P P
MCTS (Windows Applications) .Net 2.0
Never bring a sword to a gun fight

Is Multiple Exit points in a method wrong [modified]

RichardBerry4-May-07 21:46

RichardBerry

4-May-07 21:46

Hi
1) Someone told me a function should have only one exit point - why is this?

2) Is it bad practice to use the input to the function directly. In example below, I compare intInput to a constant (10). Should I first equate intInput to a local variable and then use a local variable in the comparison. Just seems like extra code to use anothe variable?

3) As opposed to using 'Return True' or 'Return False' is it better to
use the function name - E.g. 'Test = False'

Private Function Test(byVal intInput as Integer) as Boolean
If intInput >10 then
Return True
Else
Return False
End If
End Function

-- modified at 5:15 Saturday 5th May, 2007

Re: Is Multiple Exit points in a meethod wrong

Xandip4-May-07 22:59

Xandip

4-May-07 22:59

friend..
Answer to question 1 : i'm not sure of it.

Answer to question 2 : its a good practise, if u use a temporary variable
inside functions. this keeps the original value safe and secure. dont hesitate to write some more code for this, bcoz its usefull when it comes to large programs..

Answer to question 3 : there are no difference between these two, but it is good to use 'Test = False', becoz thats the correct syntax while writing a function. still it is not mandatory. the code will work...

Re: Is Multiple Exit points in a meethod wrong

RichardBerry4-May-07 23:16

RichardBerry

4-May-07 23:16

Thanks

Re: Is Multiple Exit points in a method wrong

Kevin McFarlane5-May-07 3:52

Kevin McFarlane

5-May-07 3:52

RichardBerry wrote:
1) Someone told me a function should have only one exit point - why is this?

It is an ideal but I think most developers are not religious about it. The main reason is maintainability, especially with longer, more elaborate functions. OTOH, in OO code, and in procedural code for that matter, functions should not be too long.

For the example you supply it doesn't matter much. Though it is more concise to write

Return intInput > 10

RichardBerry wrote:
2) Is it bad practice to use the input to the function directly. In example below, I compare intInput to a constant (10). Should I first equate intInput to a local variable and then use a local variable in the comparison. Just seems like extra code to use anothe variable?

No, it's not bad practice if all you're doing is effectively "reading" the input variable, as in your example. It is bad practice to modify the input variable and use the modification for subsequent processing. In this case you should take a copy.

RichardBerry wrote:
3) As opposed to using 'Return True' or 'Return False' is it better to
use the function name - E.g. 'Test = False'

This is VB .NET right? Using Return is the recommended way. Using the function name is retained only for backward compatibility.

Kevin

Re: Is Multiple Exit points in a method wrong

Dave Kreskowiak5-May-07 3:57

Dave Kreskowiak

5-May-07 3:57

RichardBerry wrote:
1) Someone told me a function should have only one exit point - why is this?

A big reason is code maintainability. One way in, one way out. If the code has to be modified, you don't have to hunt down all the exit points in a function to make sure it's returning a good value.

RichardBerry wrote:
2) Is it bad practice to use the input to the function directly. In example below, I compare intInput to a constant (10).

Yes, it is, but not for the reason you think. The first thing a function should normally do, is validate the incomming data. This may require multiple tests on multiple parameters. It may also be helpful to put the validated data in local variables so you know that you're using validated data in the rest of the function code.

RichardBerry wrote:
3) As opposed to using 'Return True' or 'Return False' is it better to
use the function name - E.g. 'Test = False'

No, it's not. Quite the opposite. In some languages, including older versions of VB, you had to assign the return value to the function name. It's far more readable and maintainable to use a Return statement. The "assign to function name" method is still in there for backwards compatibility. I wish it would just go away...

Dave Kreskowiak
Microsoft MVP
Visual Developer - Visual Basic
2006, 2007

Re: Is Multiple Exit points in a method wrong

Paul Conrad5-May-07 5:18

Paul Conrad

5-May-07 5:18

Dave Kreskowiak wrote:
One way in, one way out. If the code has to be modified, you don't have to hunt down all the exit points in a function to make sure it's returning a good value.

Excellent point. In this case, it is easiest to have a temporary boolean variable such as result and plug it in with the single return statement...

Re: Is Multiple Exit points in a method wrong

Kevin McFarlane5-May-07 12:18

Kevin McFarlane

5-May-07 12:18

Paul Conrad wrote:
In this case, it is easiest to have a temporary boolean variable such as result and plug it in with the single return statement...

I use this technique quite regularly.

Kevin

Re: Is Multiple Exit points in a method wrong

Paul Conrad5-May-07 12:29

Paul Conrad

5-May-07 12:29

Kevin McFarlane wrote:
I use this technique quite regularly.

And it pretty much works out for the best too Big Grin | :-D

Re: Is Multiple Exit points in a method wrong

RichardBerry6-May-07 23:56

RichardBerry

6-May-07 23:56

Many thanks!

By the way - Is it normal to thank someone for their reply on a forum- I feel it's just plain good manners, but on the other hand it clutters the forum...

Re: Is Multiple Exit points in a method wrong

Dave Kreskowiak7-May-07 1:16

Dave Kreskowiak

7-May-07 1:16