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Would someone please explain the concept of Delegates in a way that is a little easier to understand. The following is what I have seen in a tutorial on Delegates.
'This is how we declare a Delegate in a form class
Private Delegate Sub MyDelSub()
'Then we use the Delegate by simply declaring a variable of the Delegate and assigning the sub or function to run when called. First the sub to be called:
Private Sub WriteToDebug()
Debug.WriteLine( "Delegate Wrote To Debug Window" )
End Sub
What I don't understand is the line Private Delegate Sub MyDelSub(). Would you please explain that line a little bit? Is the word Delegate a key word in VB.NET like the words String, Function etc.? Also what is MyDelSub()? What I'd like to know in more detail are when and how to use Delegates, thank you in advance for your help.
-- modified at 20:15 Wednesday 22nd August, 2007
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ASPnoob wrote: Is the word Delegate a key word
yes
ASPnoob wrote: Also what is MyDelSub()?
The name of the delegate
You'd use delegates when you want to fire a method that calls an arbitrary number of clients, or when yuo want to cal a method in another class based on an event.
So, MyDelSub is now a type - it's a delegate which takes no arguments and doesn't return anything. Now you can do this:
Private MyDelSub OnDelete
Now, in your class methods you could do this:
if (OnDelete is not nothing ) then OnDelete()
And, you can hook OnDelete to call any method in any class you like, so long as it has this signature.
Events, such as a click event, work this way, your derived class subscribes to the delegate, and it is called when the button is clicked.
Christian Graus - Microsoft MVP - C++
"I am working on a project that will convert a FORTRAN code to corresponding C++ code.I am not aware of FORTRAN syntax" ( spotted in the C++/CLI forum )
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Hi,
I need to search for a particular phrase in a loaded page in a webbrowser and then highlight all instances of it...I know i can search thru it via the document body, but how do i highlight it to a specific color?
Thanks in advance,
Ahmad
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This might be doing it the hard way (if there is an easier way)...
Take the text. insert the appropriate html tags around each word to highlight it and then replace the document body with the new string that includes the tags...
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Hi,
I need to display a data set in some sort of table format, which will be scrollable..
This set contains approximately 500 rows of data items, say contact information.
Some rows need to be in a different color than the other rows according to some criteria which is why I can't use a big textbox.
I was thinking about several ways to implement this:
1. Using a ListView Control
2. Using a DataGrid Control
3. Using a Picture box and simply painting the item information on it. I have no need to interact with the data just display it.
4. Using a TableLayooutPanel and filling it with labels.
Which of these ways is the most efficient way to do this, performance wise, least memory requirements, best application responsiveness etc?
Thanks,
Gary
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Hi,
I only know some of these Controls, so here is a partial answer:
A PictureBox is not the solution; it does not help you whatsoever, the only
thing it tries to do reasonably well is showing an existing IMAGE. It is not
intended to be drawn upon (a Panel would fit that).
I would not choose the ListView, I expect it is tailored to the Explorer
functionality, and either too complex or not really fitting your needs.
Hence my choice would boil down to DataGrid vs. TableLayoutPanel
Hope this helps.
Luc Pattyn [Forum Guidelines] [My Articles]
this weeks tips:
- make Visual display line numbers: Tools/Options/TextEditor/...
- show exceptions with ToString() to see all information
- before you ask a question here, search CodeProject, then Google
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Not really sorry,
A picture box provides a graphics object that you may use to draw paint
whatever you like on, text included hence it can be used to show a table of data.
I may have neglected to mention this: If this data was static then I wouldn't even bother asking the question. New data is constantly received and displayed in new lines while older lines are deleted, this is my concern with performance.
The update rate is fast perhaps once a second.
Updating a ListView control therefore might seem more efficient since it only requires two actions: add and remove item. Updating the tablepanel will take a loop of 500*NumberOfColumns actions.
Which one of the ways I have listed is likely to take the least amount of CPU time?
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errorfunktion wrote: A picture box provides a graphics object that you may use to draw paint
whatever you like on
No, it doesn't. Every control that's visible has a canvas you can paint on, not the jsut the PictureBox control. The PictureBox was designed to just show an image. It loads an image and paints that image on itself.
For your situation, the ListView control would probably be the most appropriate. You'd have to remember to remove items at the beginning of the list if they are no longer needed since adding more and more items (without removing any!) will take long and longer to paint.
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I'm having problems with looping thru a datagrid to get calculations for each record. Help with my for loop will be greatly appreciated.
Dim intRec As Integer
'My Issue is Here.
For intRec = 0 To dgOrderReport.DataSource
Select Case DatePart("w", d1)
Case 1
subtract = subtract + 1
Case 7
subtract = subtract + 2
End Select
Select Case DatePart("w", d2)
Case 1
subtract = subtract + 2
Case 7
subtract = subtract + 1
End Select
absday = DateDiff("d", d1, d2) + 1 - subtract
fncGetDays = absday - CInt(2 * (absday \ 7))
If fncGetDays < 0 Then fncGetDays = 0
intRec += 1
Next
Catch ex As Exception
MsgBox(ex.Message)
End Try
Thank You<code></code>
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I cannot figure out what you're trying to do...But I do notice that you've got a For loop and you never use the counter inside of the loop for anything.
For intRec = 0 To dgOrderReport.DataSource
needs to be changed to
For intRec = 0 To dgOrderReport.DataSource.Rows.Count - 1
just for starters
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Basically what I'm trying to do is - subtract a time field in my record from my system time for each record. Business Days Only
example
order NO Name Req_date Days late
11111 Test 8/17/2007 3
Days Late is a dynamic column
I need to do this for each record - and I can not get my loop to work - when it loops it I only get the calculation for the first record and it puts that calculation in every record. Thanks For the Reply - I've changed it to a dataset so that I can use rows.count-1 -- This is what I have
For intRec = 0 To MyDataSet.Tables(0).Rows.Count - 1
Select Case DatePart("w", d1)
Case 1
subtract = subtract + 1
Case 7
subtract = subtract + 2
End Select
Select Case DatePart("w", d2)
Case 1
subtract = subtract + 2
Case 7
subtract = subtract + 1
End Select
absday = DateDiff("d", d1, d2) + 1 - subtract
fncGetDays = absday - CInt(2 * (absday \ 7))
If fncGetDays < 0 Then fncGetDays = 0
intRec += 1
Next<code></code>
Thank You
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somewhere in here you need to have something to the effect of
MyDataSet.Tables(0).Rows(intRec).Item("Days Late") = value
where do you assign this value? In one of the functions?
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' MyDataSet.Tables(0).Rows(intRec).Item("Days Late") = value '
This is the value that I'm trying to find for each record which I believe I am getting with ' fncGetDays = absday - CInt(2 * (absday \ 7)) '
after the date calculations
I'm getting that value within that loop? Should I or should I not do it that way?
I think that should be fine 
How do I get the loop to go to the next record after getting the value for the first record and so on?
Thank You
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Now that you have a dataset you can easily use the datarow approach:
<br />
Dim rw As DataRow<br />
For each rw in MyDataSet.Tables(0).Rows<br />
MsgBox(rw.Item("Days Late"))<br />
Next<br />
This will loop through each row, and will stop once there are no more rows.
Ofcourse you'll want to use rw.Item in something other than a MsgBox...
Good luck,
Johan
My advice is free, and you may get what you paid for.
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Thanks -
I'm still only getting the calculations for the first record - what in world am I missing?
Should I put this
Dim rw As DataRow
For each rw in MyDataSet.Tables(0).Rows
rw.Item("Days Late"))
Next
within my current for loop or should I just get rid of what I have and just use
the approach above?
Thank You
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So I'm still trying with this disaster loop...no luck,
I've moved things around a bit. For less confusion that I may be having...
'I create My Dynamic Data Column - Days Late
Dim dc As DataColumn
dc = New DataColumn("Days Late")
MyDataSet.Tables(0).Columns.Add(dc)
'Create my variables
Dim x As Integer
Dim row As Integer = 0
'This is my loop that does not go to the next record
For row = 0 To MyDataSet.Tables(0).Rows.Count - 1
x = DateDiff("d", dgOrderReport.Item(row, 3), System.DateTime.Today)
'Place Result into "Days late" Column
dc.Expression = x
Next row
I believe I'm missing row =+ 1 - but when I put this within my loop I get the infinite loop - I need to exit that for correct? Will this give me the results I need.?.
I've also tried it this way
'I create My Dynamic Data Column - Days Late
Dim dc As DataColumn
dc = New DataColumn("Days Late")
MyDataSet.Tables(0).Columns.Add(dc)
Dim dr As DataRow
Dim x As Integer
For Each dr In MyDataSet.Tables(0).Rows
x = DateDiff("d", dgOrderReport.Item(0, 3), System.DateTime.Today)
~~~~I have problems here - how will I give the column the value of x???
dc.Expression = dr.Item("days Late")
next dr
What is the best way to do this?
Thank You
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Don't panic.
So let's take it a step at a time:
1. Forget about your old loop (For row = 0 To MyDataSet.Tables(0).Rows.Count - 1), its a recepy for disaster.
2. Not really important, but you don't need to write next dr, just next will do.
3. Did adding the column work? Although the loop isn't really working, are you getting any errors pertaining to the dataset? If so, you may have to add a line like MyDataSet.AcceptChanges() right after you added the new column.
4. The bit: x = DateDiff("d", dgOrderReport.Item(0, 3), System.DateTime.Today) won't work. You will have to adapt it also to the new method, something like this:
dim MyDate as Date<br />
MyDate = dr.Item("Column name of the column with the date")<br />
x = MyDate.Substract(Now).Days
Or shorter still:
dim MyDate as Date<br />
MyDate = dr.Item("Column name of the column with the date")<br />
dr.Item("days Late") = MyDate.Substract(Now).Days<br />
5. I didn't quite understand whether you are trying to get the value from dr.Item("days Late") or whether you are trying to register the value of x into dr.Item("days Late"). Either way its easy enough:
Getting: x = dr.Item("days Late") (copy the value of the column to x)
Registering: dr.Item("days Late") = x (copy the value of x to the column)
Hope this works for you,
Johan
My advice is free, and you may get what you paid for.
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I am creating an application in which there is a Button and a ListView Control.
I am using VB2005.
The Subroutine below just copies the listviewitem's and subitem's text.
Controls: A button named "Search" and a listview with CheckBoxes property enabled named "lv1"
But the error comes:
System.InvalidOperationException was unhandled
Message="Cross-thread operation not valid: Control 'lv1' accessed from a thread other than the thread it was created on."
I know i have to use Delegate to Marshall Call. But i am not getting it properly.
Here is the Problem Code:
Private Sub startsearch_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles startsearch.Click<br />
Dim trd As Thread<br />
trd = New Thread(AddressOf Me.Search)<br />
trd.Start()<br />
End Sub<br />
<br />
Private Sub Search()<br />
Dim i As Integer<br />
<br />
For i = 0 To lv1.Items.Count - 1<br />
<br />
If (lv1.Items.Item(i).Checked = False) Then 'Error Comes here<br />
Debug.Write("Checked=True")<br />
Else<br />
GoTo increase<br />
End If<br />
<br />
Dim a as String = lv1.Items.Item(i).SubItems.Item(1).Text 'Here<br />
Dim b as String = lv1.Items.Item(i).SubItems.Item(2).Text 'Here<br />
Dim c as String = lv1.Items.Item(i).SubItems.Item(3).Text 'Here<br />
<br />
increase:<br />
Next i<br />
End Sub<br />
Can anyone plz give me the corrected code for the above?????
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The problem is simple. You're accessing a control from a thread other than the one the control was created on, namely the, UI thread. This is prone to problems and isn't allowed.
This code doesn't belong in a second thread since it primarily deals with the state of the contents of the control. You get no advantage by using a background thread here.
Also, the Goto statement is completely unnecessary and the logic of this section is very screwed up. Rewritten, you code should look like:
For i = 0 to lv1.Items.Count - 1
If Not lv1.Items(i).Checked Then
Debug.WriteLine("Checked=True")
Dim a As String = ...
Dim b As String = ...
Dim c As String = ...
' You might want to actually do something with these strings here...
End If
Next i
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Hi
Can anybody tell me how can I associate different event handlers for an array of controls that I have created dynamically.
Suppose I create ten buttons at runtime. I want that every button perform differnt action e.g. give a message of such type.
"You clicked" & (Button.Name)
How this can be done.
Thanks
reman
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If you are using vb.net you need to use addhandler:
Associates an event with an event handler at run time.
AddHandler event, AddressOf eventhandler
Hope that helps.
Ben
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Adding to what kubben said, you can use the same handler for all buttons,
then inside that handler use the first argument "sender", cast it to Button
and you can read the button's name, or whatever you want to access.
Luc Pattyn [Forum Guidelines] [My Articles]
this weeks tips:
- make Visual display line numbers: Tools/Options/TextEditor/...
- show exceptions with ToString() to see all information
- before you ask a question here, search CodeProject, then Google
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I am trying to get values from MS Access Db and calculate the time diff and display data in gridview using arrays but unable to do this. I am new to this coding, can some one help me on this.
Example of DB
Employeename date time inout
aaa 8/1/2007 8:00 in
aaa 8/1/2007 12:00 out
aaa 8/1/2007 13:00 in
aaa 8/1/2007 18:00 out
Out as
aaa 8/1/2007 8:00 12:00 13:00 18:00 8:00(hrs for the day)
Can someone help me on this.
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hi that's preety simple
take 2 datetime variables for 2 dates coming from database and store them as follows
dim dt1 as DateTime,dt2 as DateTime
dt1= #<fieldname of="" table="">#
dt2=#<fieldname of="" table="">#
then
dim t as TimeSpan = dt1.subtract(dt2)
then u can show using t.hours , t.minutes and t.seconds
Hope that helps
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don't forget to add field names withing the hash(#) like
dt1= #field1#
dt2=#field2#
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