Visual Basic

17-Jan-06 22:05

hi all,
i am trying to make a time control page, at a certain interval (example 10 seconds) it will fire the event.

Public Sub TimerFired(ByVal sender As Object, ByVal e As System.Timers.ElapsedEventArgs)
'my_code runs every 10 seconds
End sub

my problem is, if the process in then TimerFired runs more than 10 seconds, it will halt the current process and fire the event again and it will runs from the start, how can i lock the process and let it run the code fully in the TimerFired without being interuptted? then only re-fire the code in the TimerFired again? thanks in advance

elcheah

Joshua Quick17-Jan-06 22:24

17-Jan-06 22:24

You could disable the timer at the beginning of the event handler and then re-enable it at the end. That is if you don't mind the interval drifting a bit.

Public Sub TimerFired(ByVal sender As Object, ByVal e As System.Timers.ElapsedEventArgs)
   myTimer.Enabled = False
   ' Do something...
   myTimer.Enabled = True
End sub

Or you could block an interrupting event's entry by using a simple flag. An old school approach.

Private m_isBusy As Boolean = False
Public Sub TimerFired(ByVal sender As Object, ByVal e As System.Timers.ElapsedEventArgs)
   If (m_isBusy) Then Return
   m_isBusy = True
   ' Do something...
   m_isBusy = False
End sub

elcheah17-Jan-06 23:09

17-Jan-06 23:09

thanks for the fast reply! i have tried the old school approached but it does not work, coz

Public Sub TimerFired(ByVal sender As Object, ByVal e As System.Timers.ElapsedEventArgs)
If (m_isBusy) Then Return
m_isBusy = True
' Do something...
m_isBusy = False <-------
End sub

i could not reach the code above and it is already interupted, and it end up without firing the TimerFired event anymore, and the 1st method works fine, thanks alot... Smile | :)

Joshua Quick18-Jan-06 7:15

18-Jan-06 7:15

I'm surprised using a flag didn't work for you. As long as you check the flag at the top of the method and it doesn't ever return out before clearing the flag, it should work. Or perhaps an exception is being thrown and being caught somewhere else in the code? That would prevent the flag from getting cleared at the bottom too.

In any case, I'm glad you got your code working using the other method. If you're happy with it, then I am too. Smile | :)

elcheah18-Jan-06 14:50

18-Jan-06 14:50

hi,
i have another question, why is it the program still keep firing the TimerFired event, when i try stop the TimerFired event after caling myTimer.enabled?

Joshua Quick18-Jan-06 15:30

18-Jan-06 15:30

elcheah wrote:
why is it the program still keep firing the TimerFired event, when i try stop the TimerFired event after caling myTimer.enabled?

It shouldn't. If you disable the timer like this...
myTimer.Enabled = False
...then it shouldn't be calling that method anymore.

Perhaps your timer is being re-enabled elsewhere in your code?
Perhaps you have another timer being handled by that same method?

How are you setting up your timer anyways? The code you showed doesn't have a Handles keyword postfixed to the method, which tells me that you're not setting it up via WithEvents. Are you using AddHandler instead? Or a delegate?

elcheah18-Jan-06 15:57

18-Jan-06 15:57

ya, i am using AddHandler in Page_load,

Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load<br />
<br />
AddHandler myTimer.Elapsed, AddressOf TimerFired<br />
<br />
End sub<br />
<br />
Public Sub TimerFired(ByVal sender As Object, ByVal e As System.Timers.ElapsedEventArgs)<br />
' My_code<br />
End sub

then i control the timer with 2 buttons (start,stop) by using MyTimer.Enabled = True,MyTimer.Enabled = False. Is that a wrong way of coding? Unsure | :~

Joshua Quick18-Jan-06 16:23

18-Jan-06 16:23

Now we're getting somewhere. :->
I see a few possible issues here.

(1)
You need a RemoveHandler for every AddHandler that you have. If you don't call RemoveHandler, then your timer will continue to persist in memory, even after your form has been closed. This is because a reference is still being kept alive by the AddHandler function.
The best place to call RemoveHandler is in your form's Closed event handler.

However, an even easier solution is to use a timer control on your form instead, via the designer. The designer will automatically declare the timer member with the "WithEvents" keyword, which automatically hooks up event handlers for you at compile time. When you select its Tick event from the IDE's drop down box, it'll insert that method postfixed with the "Handles" keyword.

(2)
Watch out when using the System.Timers.Timer class. By default, this timer operates on another thread which can cause race conditions when used on a form. You can avoid this issue by synching the timer to your UI's thread. However, an even easier solution is to use System.Windows.Forms.Timer instead, which is a control that's selectable in the UI designer, under the Form section.

(3)
You shouldn't use Timer.Enabled to block access to the TimerFired() method if you're controlling the timer enable from the Form too. This could put the timer in a bad state. Instead you should use a flag like I stated before, which should work once you fix the above issues.

elcheah18-Jan-06 18:03

18-Jan-06 18:03

hi, i have trouble with the 1st issue u mentioned, can you show me a simple piece of code on how it is done? i have tried but counldn't get it done Frown | :(

Thank you very very much ...

Joshua Quick18-Jan-06 18:23

18-Jan-06 18:23

You need to handle the Form Closed event. The IDE will automatically create this method for you by going to the form source code, select (Form Events) from the top left combo box, and then select Closed from the top right combo box.

Then you can remove the event handler as follows...

RemoveHandler myTimer.Elapsed, AddressOf TimerFired

Notice how it looks similar to your AddHandler. All you have to do is copy your AddHandler line and replace Add with Remove. It's important that the object reference and the method address exactly match the AddHandlers parameters.

elcheah18-Jan-06 21:17

Calling C function in VB.net

18-Jan-06 21:17

at last i got it,you really helped me alot! thanks for the explanation and guidance, thank you very much! Big Grin | :-D

jpvillemagne17-Jan-06 22:04

17-Jan-06 22:04

Hi everybody,

I have to use an API for a CAN board that only exist in C langage. and I've got a problem with a C function that use a void* parameter.
in VB6 I used the any type but it doesn't exist in .net

so I found example on MSDN that use < MarshalAs( UnmanagedType.AsAny )> ByVal Myparam to replace any

it works fine to pass data to the function but it doesn't work to get data form the function

Does somebody already do that?

Thanks for your help

JP

Guffa18-Jan-06 1:08

Guffa

18-Jan-06 1:08

If the function uses the pointer to return data, the pointer has to point to a structure that is large enough to hold the data that the function writes to it.

You also have to know how the data is structured to read it.

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jpvillemagne26-Jan-06 0:28

26-Jan-06 0:28

Thank you for your answer,

I did some test whith a simple C function and I succeed to localize the problem (but not the solution...)

the stuct I used is the following in C :
typedef struct{
int valint;
double valdouble;
char ValString[8];
}t_TestData;

When I call the function in VB I déclare the strcuture like that :
Public Structure t_TestData
Dim valint As Integer
Dim valdouble As Double
<vbfixedarray(8)> Dim Data() As Char
Public Sub Initialize()
ReDim Data(8)
End Sub
End Structure

valint and valdouble are updated correctly but not the Array Data
I call Initialize before calling the C function and I tried with the folowing declarations
Declare Sub TestDll Lib "TestvoidParam.dll" (ByVal t As Integer, ByRef TestData As t_TestData)
or
Declare Sub TestDll Lib "TestvoidParam.dll" (ByVal t As Integer, <marshalas(unmanagedtype.asany)> ByVal TestData As Object)

but it doesn't work, I've got an unknown exception. So the problem is to Get the Data of a fix size array of a structure.

have you got an idea?

Thanks

JP

If the structure is without

Guffa27-Jan-06 7:06

Guffa

27-Jan-06 7:06

There are no fixed size arrays in .NET. Your Data member is a reference to an array object, and the ReDim statement is really:

Data = New Char(8)

If the C structure contains the array as a value type, the structure contains the character data itself, not a reference.

Test if declaring characters as value types in the structire gets you any closer:

Dim Data0 as Char
Dim Data1 as Char
Dim Data2 as Char
Dim Data3 as Char
Dim Data4 as Char
Dim Data5 as Char
Dim Data6 as Char
Dim Data7 as Char

Another thing that might cause you problem is if the char datatype is not a unicode character as in .NET. Then you have to declare the data as bytes and convert it to characters.

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jpvillemagne1-Feb-06 21:21

1-Feb-06 21:21

Thank you very much for your help,

it works when I declare 8 char Data (the C char is also unicode character).
I've got a C structure with an array of 256 char so I have to declare 256 Char in my VB struct!!!
Not very smart Smile | :)

thanks again

JP

Guffa1-Feb-06 21:40

Guffa

1-Feb-06 21:40

Perhaps the MarshalAs[^] attribute can be used for this.

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jpvillemagne1-Feb-06 23:10

1-Feb-06 23:10

I found the solution ,

my structure is define like that in vb

Public Structure t_TestData
Dim valint As Integer
Dim valdouble As Double
<marshalas(unmanagedtype.byvalarray, sizeconst:="9)"> Dim Data() As Char
End Structure

And it works

Thanks for your help

JP

jpvillemagne1-Feb-06 23:14