Android Question Cannot CLV.JumpToItem before ShowPage

Ilya G. · May 21, 2022

I want to show the page when all items are loaded into the CLV to avoid the list flickering, but in this case CLV.JumpToItem doesn't work. Is that normal or its a bug?

B4XMainPage:

HomePage.Initialize
B4XPages.AddPage("Home", HomePage)

ChatPage.Initialize
B4XPages.AddPageAndCreate("Chat", ChatPage)

HomePage:

Sub CustomListView1_ItemClick (Index As Int, Value As Object)
    B4XPages.MainPage.ChatPage.UpdateMessages(Value)
End Sub

ChatPage:

Sub UpdateMessages (m As Map)
    CustomListView1.Clear
'    CustomListView1.sv.ScrollViewOffsetY = 0
    
    Private Cursor As Cursor = Starter.SQL.ExecQuery("")
    Private Value As Map

    For i = 0 To Cursor.RowCount - 1
        Cursor.Position = i
        Value.Initialize

        For c = 0 To Cursor.ColumnCount - 1
            Value.Put(Cursor.GetColumnName(c), Cursor.GetString2(c))
        Next
        
        Private label As Label
        label.Initialize("")
        label.TextSize = 15
        label.SetLayoutAnimated(0, 0, 0, CustomListView1.AsView.Width - 100dip, 20dip)
        
        Private holder As B4XView = XUI.CreatePanel("")
        holder.SetLayoutAnimated(0, 0, 0, CustomListView1.AsView.Width, 40dip + Max(20dip, SU.MeasureMultilineTextHeight(label, Cursor.GetString("message"))) + 15dip)

        CustomListView1.Add(holder, Value)
    Next
    Cursor.Close

    If CustomListView1.Size > 0 Then
        Sleep(0)
        CustomListView1.JumpToItem(CustomListView1.Size - 1)
        CustomListView1.Refresh
    End If
    
    B4XPages.ShowPage("Chat")
End Sub

Sandman · May 21, 2022

GanjaKyp said:
in this case CLV.JumpToItem doesn't work

Please post error message.

Ilya G. · May 21, 2022

there is no error, just CLV.JumpToItem doesn't show the last item

Alexander Stolte · May 21, 2022

GanjaKyp said:
Sleep(0)

Try a Sleep(250) and if this works try a Sleep(50)

Ilya G. · May 22, 2022

Alexander Stolte said:
Try a Sleep(250) and if this works try a Sleep(50)

No, that doesn't help either, I tried 1000ms too. I made a small example, on the first launch of the application, JumpToItem does not work

LucaMs · May 22, 2022

Move B4XPages.Showpage from the chat page to the MainPage:

B4X:

Private Sub Button1_Click
    ChatPage.UpdateMessages
    B4XPages.ShowPage("Chat")
End Sub

(however I don't know why it doesn't work your way)

Ilya G. · May 22, 2022

LucaMs said:
Move B4XPages.Showpage from the chat page to the MainPage

I want to show the page when all items are loaded into the CLV to avoid the list flickering:

LucaMs · May 22, 2022

LucaMs said:
(however I don't know why it doesn't work your way)

I didn't notice that there is also the CustomListView1_VisibleRangeChanged event-routine; this is what gives problems with the jump.

GanjaKyp said:
I want to show the page when all items are loaded into the CLV to avoid the list flickering:

To do that you must...

B4X:

Sub UpdateMessages As ResumableSub
' ...
    Return True ' It doesn't matter if True or False.
End Sub

B4X:

Wait For (ChatPage.UpdateMessages) Complete(Unused As Boolean)

Ilya G. · May 22, 2022

LucaMs said:
B4X:

Wait For (ChatPage.UpdateMessages) Complete(Unused As Boolean)

Unfortunately exactly the same problem with the jump ?

LucaMs · May 22, 2022

GanjaKyp said:
Unfortunately exactly the same problem with the jump ?

LucaMs said:
there is also the CustomListView1_VisibleRangeChanged event-routine; this is what gives problems with the jump.

Ilya G. · May 22, 2022

So this is a CLV bug?

LucaMs · May 22, 2022

GanjaKyp said:
So this is a CLV bug?

I'm not sure; I should study that event a little bit, but possibly later, not now.

Ilya G. · May 22, 2022

Thanks a lot, its really stopped the whole process

Alexander Stolte · May 22, 2022

GanjaKyp said:
I want to show the page when all items are loaded into the CLV to avoid the list flickering:

You can also place a panel over the CLV and with ".SetVisibleAnimated(250,False)" you smoothly hide it when the list is loaded, then the user has a nice smooth transition. I use this trick in some customviews where I have the CLV in use to avoid exactly this problem.

Ilya G. · May 22, 2022

In this case, I think this is not be very beautiful

Spavlyuk · May 23, 2022

Have you tried CLVBackwards?

[B4X] CLVBackwards - xCLV extenstion for lists that grow backwards

This class can be helpful in esoteric cases where the list grows up instead of down. Think of a chat app where you start with the most recent messages and when the user scrolls up, more older messages are added to the top. The challenge here is to add items without making the list jump back and...

www.b4x.com

Ilya G. · May 23, 2022

Spavlyuk said:
Have you tried CLVBackwards?

[B4X] CLVBackwards - xCLV extenstion for lists that grow backwards

This class can be helpful in esoteric cases where the list grows up instead of down. Think of a chat app where you start with the most recent messages and when the user scrolls up, more older messages are added to the top. The challenge here is to add items without making the list jump back and...

www.b4x.com

I tried, but it seemed to me that the inconvenience is more than the benefits

teddybear · May 24, 2022

Move B4XPages.ShowPage("Chat") to B4XMainPage , CLV.JumpToItem works fine,see below

GanjaKyp said:
I want to show the page when all items are loaded into the CLV to avoid the list flickering, but in this case CLV.JumpToItem doesn't work. Is that normal or its a bug?
Sub UpdateMessages (m As Map)
......
B4XPages.ShowPage("Chat") '<=== Move it to B4XMainPage
End Sub

GanjaKyp said:
B4XMainPage

Private Sub Button1_Click
B4XPages.ShowPage("Chat") '<= It should be showed first
ChatPage.UpdateMessages
End Sub

Ilya G. · May 25, 2022

teddybear said:
Move B4XPages.ShowPage("Chat") to B4XMainPage , CLV.JumpToItem works fine,see below

If you do this, you can see how the list is rendered, so I would like to do this before the page is shown

Ilya G. · May 25, 2022

@Erel, perhaps you can tell what is the reason for this behavior?

Android Question Cannot CLV.JumpToItem before ShowPage

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