Event on Scrolling to the end in flowlayoutpanel

[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.

[Ammar_Ahmad]

Err my laptops fan got fried - is at the repair shop. - sorry for the late reply... Anyway. So you mean I should just call this function on load? and replace the maxscroll = index - 18 on load?

[Nick Otten]

Hey, Sorry for my late response. I unfortunately fell ill. to get back to your question: No, you call that function every time after the amount of items in your flowlayoutpanel changes.

[Ammar_Ahmad]

so all the code needs to be same. but what should I do with: maxscroll = index - 18 ? the index property was giving an error in flowlayoutpanel. can you give me the example on the same code or better on the project its self.. :

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
End Property

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

[Nick Otten]

hmm oke i admid my code was a bit of mess. i cleared it out a bit and made a example program so you can see how it works. Please follow the below steps. 1. start a new form project 2. Add is Listbox. set the name to txtscroll and the size to 254; 381 3. Add a button, call this one btnadd 4. copy paste the following code into the project (under the form you just made)

Imports System.Runtime.InteropServices

Public Class Form1

#Region "declarations"
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
Private index As Int32 = 0 'used for random loops to fill the txtscroll
Private Const SB_HORZ As Integer = &H0
Private Const SB_VERT As Integer = &H1
#End Region

#Region "dll calls"
'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

#End Region

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