Event on Scrolling to the end in flowlayoutpanel

Nick Otten

Hey, there is a scroll event for controls. see this[^] for info and how to get/use it. Nick

Ammar_Ahmad

So I tried to do something like that today.

    If e.NewValue = e.OldValue Then
        MsgBox("hi")
    End If

but it is not working the way I want it to work... The problem is that now if I click the arrows on the scroll bar, then only it works, if I use the (bar) *not the left/top right/bottom arrows, it shows the message box like 100x times. but even then I am having a problem. the problem is that, when I scroll back to the beginning, it shows that message box again.

Nick Otten

Perhaps its not as MS once intended it. or perhaps it is...but the scrolling and value changed are two differed events. if you press one of the scrolls arrows the program will make it scroll in that direction once. and then change the value. but when you drag the bar you scroll every time you move a little...but the value is only changed upon the key release. a easy thing to do is to declare a private boolean (outside the event). and switch it true/false so the message box only displays once.

Private ScrollingMessage as Boolean = true 'I know not the right place to declare it... put it with your other declarations

'put this below into your event
If e.NewValue = e.OldValue and ScrollingMessage Then
MsgBox("hi")
ScrollingMessage = false
elseif e.NewValue <> e.OldValue then
scrollingmessage = true
End If

Ammar_Ahmad

yeah but this still causes the issue of 100x message boxes that are displayed when I use the bar instead of the arrows. Edit: And the issue of back scroll is still there..

Nick Otten

Oke started a little project to test a bit around and i think you might find this interesting. i used a form called form1. and placed a listbox on it i called txtscroll. I suggest you make a same sort of window and paste the following code in to see how it works:

Public Class Form1

Dim WithEvents scrollhandler As MyListener 'class that will watch windows to see if your scrolling
Private scrolled As Boolean = False 'boolean you can use to flip if a message box was displayed or not...(so it wont loop the messagebox.show)


Private Sub Form1\_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    'some random loop i used to ditch some data in my listbox for testing
    Dim index As Int32 = 0
    Do While index < 100
        txtscroll.Items.Add(index.ToString())
        index += 1
    Loop

    'attach your scrollwatcher to your control. in my case i have a listbox called "txtscroll")
    scrollhandler = New MyListener(txtscroll)

End Sub

Private Sub scrollhandler\_MyScroll(ByVal sender As Object, ByVal e As System.EventArgs) Handles scrollhandler.MyScroll
    'place your if/else statement here, its smart to use the scrolled boolean to flip true/false so the messagebox doesnt go on a loop
End Sub

Private Sub txtscroll\_MouseWheelScroll(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles txtscroll.MouseWheel
    scrollhandler\_MyScroll(e, e) 'needed to catch the scrollwheel event.
End Sub


Private Class MyListener
    Inherits NativeWindow

    Public Event MyScroll(ByVal sender As Object, ByVal e As EventArgs)
    Const WM\_MOUSEACTIVATE = &H21
    Const WM\_MOUSEMOVE = &H200
    Private control As Control

    Public Sub New(ByVal control As Control)
        AssignHandle(control.Handle) 'docks handler to given control
    End Sub

    Protected Overrides Sub WndProc(ByRef Messageevent As Message)
        Const WM\_HSCROLL = &H114
        Const WM\_VSCROLL = &H115
        If Messageevent.Msg = WM\_HSCROLL Or Messageevent.Msg = WM\_VSCROLL Then 'looks if the horisontal or verticle scrollbar is moving
            'one of the scrollbars is moving, throw event
            RaiseEvent MyScroll(control, New EventArgs)
        End If
        MyBase.WndProc(Messageevent)
    End Sub

    Protected Overrides Sub Finalize()
        'not used in example but drops the

Luc Pattyn

private int previousValue;

public void someEventHandler(...) {
int currentValue=...;
if (currentValue==extremeValue && currentValue!=previousValue) doWhatEver();
previousValue=currentValue;
}

:)

Luc Pattyn [My Articles] Nil Volentibus Arduum

Nick Otten

oeh quite nice! might actually try that in the future. but isn't that C#?

Luc Pattyn

I'd call it pseudo-code around here :-D

Luc Pattyn [My Articles] Nil Volentibus Arduum

Nick Otten

1-0 for you ;)

Ammar_Ahmad

Thanks for the example. but I still can't figure out how I can use this to know if the user has scrolled to the end.

Ammar_Ahmad

isn't previousValue a readonly value?

Luc Pattyn

did I declare it read-only? :confused:

Luc Pattyn [My Articles] Nil Volentibus Arduum

Ammar_Ahmad

Seems like I misunderstood the algorithm.

Nick Otten

hmm, oke im not really sure why you want to show that messagebox. but I thrown in some more trail and error and i came up with the code below. Note that I ran a little low on time so its a bit of a mess...i recommend throwing in a breakpoint to figure out exactly how the code works before putting it into your project. to test it again make a form (called form1) and add a listbox (txtscroll) in it. then copy paste the code into your form.

Imports System.Runtime.InteropServices

Public Class Form1
Dim WithEvents scrollhandler As MyListener 'class that will watch windows to see if your scrolling
Private scrolled As Boolean = False 'boolean you can use to flip if a message box was displayed or not...(so it wont loop the messagebox.show)
Private maxscroll As Int64 'int used to store the max value of the scrollbar
'dll used to get the scrollbar value NOTE: if the scrollbar is not visible or you go higher then your max it will crash!
_
Public Shared Function GetScrollPos(ByVal hWnd As IntPtr, ByVal nBar As Integer) As Integer
End Function

'dll used to set the scrollbar value NOTE: if the scrollbar is not visible or you go higher then your max it will crash!
\_
Private Shared Function SetScrollPos(ByVal hWnd As IntPtr, ByVal nBar As Integer, ByVal nPos As Integer, ByVal bRedraw As Boolean) As Integer
End Function

Private Const SB\_HORZ As Integer = &H0
Private Const SB\_VERT As Integer = &H1


Public Property HScrollPos() As Integer 'property to set or get the horisontal scrollbar value
    Get
        Return GetScrollPos(DirectCast(txtscroll.Handle, IntPtr), SB\_HORZ) 'change txtscroll to the control you use. dont forget the .handle
    End Get
    Set(ByVal value As Integer)
        SetScrollPos(DirectCast(txtscroll.Handle, IntPtr), SB\_HORZ, value, True) 'change txtscroll to the control you use. dont forget the .handle
    End Set
End Property


Public Property VScrollPos() As Integer 'Property to set or get the Vertical scrollbar value
    Get
        Return GetScrollPos(DirectCast(txtscroll.Handle, IntPtr), SB\_VERT) 'change txtscroll to the control you use. dont forget the .handle
    End Get
    Set(ByVal value As Integer)
        SetScrollPos(DirectCast(txtscroll.Handle, IntPtr), SB\_VERT, value, True) 'change txtscroll to the control you use. dont forget the .handle
    End Set

Ammar_Ahmad

Did you test the code...? Well... Because the above didn't work for me. I made a test project to see how it works. but it didn't show me any message...

Nick Otten

Did you recalculate the max value of your scrollbar? if your listbox is of a differed size then mine (witch it probably is) you have to recalculate it. just run the program. dont scroll and see how many items fit into the listbox (for me that where 18). you want to do the index - [the number you found]. after that it should work.

maxscroll = index - 18 'calculate max value. everytime you add a item you have to do this again. to calculate this its a bit of a trail and error thing depending on your control

Ammar_Ahmad

Oh that kinda worked... but how am I ganna calculate the value in a control like this one: When its normal screen size: http://foto.pk/images/minx.png[^] When its maximized: http://foto.pk/images/maxx.png[^] ------------------------------------------------------------- Btw. You asked why would I want to know this value before... Answer) I don't actually want to show users "yay u reached the bottom" lol. I want the program to get more tweets when it reaches there. The above that I am making is a v2 of my current twitter client called TRocket. TRocket - Twitter Client [Open Source][^]

Nick Otten

How do you fill the listbox? with a loop or a data binding? EDIT: oke something just shot to my mind. the items you add to your listbox are controls right? i forgot the object name but i've seen the code of those. this means they have a fixed sized right? you could calculate how much fit into your listbox if you read out the length and hight of it. lets say for example your listbox is 300 pixels wide and 400 pixels high. your controls are 100 wide and 50 high. this would mean you can fit 3 rows of each 8 items = 24 items without scroll bar. so in a 'math' way:

[ammount of items] - (math.floor([with_listbox]/[with_control])+math.floor([hight_listbox]/[hight_control])) = maximum scroll value

------------------- Ah oke, yea now its making sense ;) and i already figured it was for Trocket (read the thread about it) when i was helping you with a previous question.

Ammar_Ahmad

huh? Sorry but I didn't quiet get that... wasn't quiet good in maths :/ Can you check into the source code: http://www.mediafire.com/?m13i05h0vmb11yc[^] I actually want this to be on Flowlayoutpanel1.

Nick Otten

Private Function CalculateMaxScrollValue(ByVal totalitems As Int64, ByVal controlhight As Int32, ByVal controlwith As Int32)
'NOTE: 482 and 114 is the size property of your msgctrl.vb
Return totalitems - (Math.Floor(controlwith / 482) * Math.Floor(controlhight / 114))
End Function

Add that function to your code to find the max scroll value. Use that in combination with the code i send you in the previous posts in this topic. replace the txtscroll with the flowlayoutpanel1 and it should work (cant test it here). as a side note: you might want to fine tune the if/else of mine a little to a "<" instead of "=". giving a exact value to a 'analog' control gives it a small change to trigger. also it seems like the program is single threaded. i don't know how long it takes to load those messages but your interface will hang (not responding ect) till the load is complete. looking into threading might be interesting.