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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.
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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  Thank you very very much ...
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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.
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at last i got it,you really helped me alot! thanks for the explanation and guidance, thank you very much!
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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
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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.
---
b { font-weight: normal; }
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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
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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.
---
b { font-weight: normal; }
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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 
thanks again
JP
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Perhaps the MarshalAs[^] attribute can be used for this.
---
b { font-weight: normal; }
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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
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oops I did a mistake when I post the message (forget to check ignore HTML....)
the structure is
Public Structure t_TestData
Dim valint As Integer
Dim valdouble As Double
<MarshalAs(UnmanagedType.ByValArray, SizeConst:=9)> Dim Data() As Char
End Structure
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I want open mycomputer,control panel,Accessories and other windows components through VB.net.
Please help me.
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You're going to have to be more specific about this. Each of these would require its own method to open. Some of which might not result in what you were expecting.
What exactly do you mean by "open"? What are you trying to do with this functionality?
RageInTheMachine9532
"...a pungent, ghastly, stinky piece of cheese!" -- The Roaming Gnome
-- modified at 10:13 Wednesday 18th January, 2006
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I have a client who wants a Windows Form with about 5 large datagrids on it. Since some of these may not be applicable to the current user we want to be able to make each datagrid collapsable/expandable so that just the header row is visible. How could I go about inserting a custom icon (a "+" and "-" which would interchange depending on the current collapsed state - as in Explorer or the TreeView control) on the DataGrid header row?
I've googled this but can't find anything similiar - I've also got a tight deadline so am hoping someone can point me in the right direction!
TIA...
Mike
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If they're not applicable to the current user, why show them at all? It goes against standard practices.
There's no built in support for this in the DataGrid control. You'd have to create your own DataGrid control, inheriting from DataGrid, and providing the properties and code to ownerdraw the headers yourself. You might want to Google for "ownerdraw datagrid" for something similar before attempting to tackle this. Your deadline might prevent you from implementing it.
RageInTheMachine9532
"...a pungent, ghastly, stinky piece of cheese!" -- The Roaming Gnome
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Thanks Dave... that's what I suspected.
Since we don't have time to an "ownerdraw" solution what I've ended up doing is dynamically creating a button control and adding a click event for it which sets the DataGrid.Height property as required. The button is created Ok but the problem I'm having now is that it does not display over the top left hand corner of the DataGrid as I need it to - it's actually getting positioned in the right location but *under* the datagrid... how do I force the new button to display over the top of the DataGrid (ie: at position 0,0 in the caption)? Is there some sort of z-index as there is in HTML forms? (See the code below to see what I'm doing.)
Also, I want to be able to make the scrollbars in the grid non-visible when it collapses then re-show them when it expands - I guess it's the same problem where I'd need to draw/hide the scrollabrs myself by overriding the appropriate method or event in the DataGrid control - any thoughts on this? I don't believe there is any access to DataGrid scrollbars except via a custom DataGrid control but if you (or anyone else) knows how to do this I'd be grateful!
Cheers,
Mike
<br />
...<br />
'NB: dg1 is my DataGrid<br />
dg1.DataSource = _dataSet.Tables("customers")<br />
dg1.CaptionText = " Customers" 'Allow room for the collapse/expand button in the caption row.<br />
<br />
'Now add the expand/collapse button dynamically over the left hadn top corner of the DataGrid.<br />
Dim btnCollapse As New Button<br />
btnCollapse.Height = 20<br />
btnCollapse.Width = 20<br />
btnCollapse.FlatStyle = FlatStyle.Flat<br />
btnCollapse.Top = dg1.Top<br />
btnCollapse.Left = dg1.Left<br />
btnCollapse.Text = "-"<br />
btnCollapse.BackColor = Color.AliceBlue<br />
btnCollapse.ForeColor = Color.Navy<br />
btnCollapse.Name = "btnCollapse"<br />
btnCollapse.TabIndex = dg1.TabIndex + 1<br />
AddHandler btnCollapse.Click, AddressOf Me.btnCollapse_Click<br />
Me.Controls.Add(btnCollapse)<br />
...<br />
End Sub
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You could try calling the button's .BringToFront method to get the control to appear on top of the DataGrid. There may be some pitfalls to doing this, like the DataGrid overpainting the button anyway, but that's about the best method you've got right now.
RageInTheMachine9532
"...a pungent, ghastly, stinky piece of cheese!" -- The Roaming Gnome
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Thanks again Dave... I've got it working on a Form with a DataGrid dragged onto it. I now need to make a custom control (which inherits from DataGrid) but has the same ability to add the expand/collapse button dynamically. However, I can't work out which Method or Event I need to override and add the new button code to... I tried it in OnControlCreated and OnPaint (first calling each's respective MyBase method) but it just gets ignored... any advice on where I'd put something like this?
Sorry to be a pain - it's very difficult to work out where to put this stuff with all the events and methods supported by .Net controls!
Cheers,
Mike
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OK, I think I got you confused a bit. If you're just going to create a control using existing components, then you'll want to create a User Control, inheriting from UserControl, NOT Control, or any other control.
You'll drop a DataGrid and your Button onto the designer. I think it's pretty intuitive from there. You'll initialize your instance of your control in the New method, not in any event. It's kind of the quick and dirty method to slap a control together. Really what you putting together is a wrapper around your datagrid and button to manage what they look like when the button is clicked. Your control code will just be handling the normal events and properties of the button and datagrid. About the only UserControl related event you'll have to deal with is the Resize.
I can think of a few pitfalls in putting this together.
The first is tracking what the height of your control would be expanded and colapsed. You'll have to track the current state of the control and modify you constituent controls to match the look your after.
To get rid of the scroll bars on the datagrid, you'll just have to set it's scrollbars property to None. Remember to restore this when you expand the control back to normal size.
RageInTheMachine9532
"...a pungent, ghastly, stinky piece of cheese!" -- The Roaming Gnome
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Dave, thanks again for replying. I was wondering if I needed a UserControl instead so had planned to play around that today - I've only ever written a couple but, as you say, they're pretty intuitive. I still need a custom datagrid control but that's just to add some common methods and properties etc... so when I've done that I'll drag both that and the button on to a new user control and go from there.
With the collapsed and expanded heights I worked out the ideal height of the Caption Row (which we are always using) and I simply make the button that height. I also shift the caption over about 8 spaces to make room for it at the top left of the capton bar - so far it work well - even if it's not the most elegant solution!
Cheers,
Mike
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Hi Developers,
I have been working in Web Application using ASP.net since a long time. In Web we have great facility of Style Sheets to follow the consistant format of different controls, like labels,tables,textfields etc. If we change the style in Style Sheet the changes appear in the whole application.
Can I have such flexibility and consistancy in desktop application using VB.net. I have heard something abt Control Collection but dnt know much abt it. Please suggest me its solution.
Thanks in advance
Lets work it Out.........!
-- modified at 3:11 Wednesday 18th January, 2006
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The Control collection is a collection of child controls on the Control (remember that a form is also a form of control - excuse the pun) and has nothing to do with the style of controls.
ColinMackay.net
"Man who stand on hill with mouth open will wait long time for roast duck to drop in." -- Confucius
"If a man empties his purse into his head, no man can take it away from him, for an investment in knowledge pays the best interest." -- Joseph E. O'Donnell
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There's no such thing as a style sheet in Windows Forms. You'd have to implement Skinning functionality in your code. Google for vb.net skinning[^] for examples and 3rd party libraries.
RageInTheMachine9532
"...a pungent, ghastly, stinky piece of cheese!" -- The Roaming Gnome
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fValue = TextWidth(lstCtrl.List(iIndex))
I got "compile error" message for the above code saying "Sub or Function not defined".
The code is in the following sub by Joshua Quick. Please tell me how to fix it, thanks.
' Analyzes given listbox and displays a horizontal scroll bar if needed.
Public Sub UpdateHorizontalScrollbar(lstCtrl As ListBox)
Dim fMax As Single
Dim fValue As Single
Dim iIndex As Integer
' Get length of longest text in listbox.
fMax = 0
For iIndex = (lstCtrl.ListCount - 1) To 0 Step -1
fValue = TextWidth(lstCtrl.List(iIndex))
If (fValue > fMax) Then fMax = fValue
Next
' Convert max text length to pixels.
fMax = fMax / Screen.TwipsPerPixelX
' Increase length for checkboxes and margins (in pixels).
If (1 = lstCtrl.Style) Then fMax = fMax + 13 ' Offset for checkbox.
fMax = fMax + 4 ' Offset for margins.
' Set horizontal scrollbar length.
SendMessage lstCtrl.hWnd, &H194, CLng(fMax) + 1, 0&
End Sub
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