B4A Library xListview

KZero · Mar 17, 2020

xCLV now supports adding huge numbers of items smoothly using Preoptimized class , you should use it instead :

[B4X] PreoptimizedCLV - Lazy loading extension for xCustomListView

This is a cross platform class that extends xCustomListView and makes it "lazier". Lazy loading is explained here: https://www.b4x.com/android/forum/threads/b4x-xui-customlistview-lazy-loading-virtualization.87930/#content and here...

www.b4x.com

I'd like to share my first B4A library,

Using xListview you can add tens of thousands of items instantly with an extremely low memory footprint.

How it works
instead of creating an empty panel for each item to load the layout inside it when needed, which takes time to create the panels and consumes more memory if used for a large number of items
xListview on the other hand uses only 1 panel for each visible item and automatically destroys it when it goes offscreen.
So if we have a list that contains 100,000 items it will actually have around 15 panels only.

Requirements
Reflection library

test on a very old android device

Usage

B4X:

Sub Globals
    Private xLV As xListView
    Private lblTitle As Label
    Private lblTime As Label
End Sub
Sub Activity_Create(FirstTime As Boolean)
    Activity.LoadLayout("L1")
    xLV.selectionColor = Colors.Cyan
    xLV.OffscreenItems=5 'Default = 5, change it before adding items
    xLV.SetScrollbarColor(Colors.Blue)
    xLV.HideScrollBar(False) ' Set True to hide Scrollbar
End Sub
Sub xLV_PanelRequested(Index As Int)
    'Load the panel here , the panel will be automatically removed when it's not visible (don't remove it manually)
    Dim P As Panel
    P.Initialize("")
    P.SetLayout(0,0,xLV.AsView.Width,180dip)
    P.LoadLayout("ItemLayout") 'Disable animation from the Visual Designer for more smooth scrolling
    lblTitle.Text= "Item Number : " & Index
    xLV.LoadPanel(P,Index)
End Sub
Sub Button1_Click
    Dim B As Button=Sender
    B.Text="Clicked"
End Sub
Sub xLV_ItemClick (Index As Int, Value As Object)
    ToastMessageShow("Item " & Index & " Clicked",False)
End Sub
Sub xLV_ItemLongClick (Index As Int, Value As Object)
    ToastMessageShow("Item " & Index & " Long Clicked",False)
End Sub
Sub btnAddItems_Click
    Dim ms As Long = DateTime.Now
    For i = 1 To 10000
        xLV.NewItem(180dip,i)
    Next
    xLV.Reload ' you must call reload after adding new items
    lblTime.Text = "Load Time : " & (DateTime.Now - ms) & " ms    -   Total Items : " & xLV.Size
End Sub

v0.9
+ Resize item
+ DisableSelectionColor

v0.95
+ Scrolling performance improved

janderkan · Mar 17, 2020

This looks good, excited to see the B4X implementation.

LucaMs · Mar 17, 2020

https://www.b4x.com/android/forum/threads/b4x-xui-customlistview-lazy-loading-virtualization.87930/

KZero · Mar 18, 2020

LucaMs said:
https://www.b4x.com/android/forum/threads/b4x-xui-customlistview-lazy-loading-virtualization.87930/

did you try to add 100,000 items with clv ?
clv is not suitable for such large numbers of items

Erel · Mar 18, 2020

It is true that xCLV (currently) creates a panel for each item. With lazy loading you can create long lists.
One of the reasons that I don't think that it is a big issue is that a user will never scroll 100k items. This is not practical.

Edit: while there is never a good reason to add 100k items to a UI list, you can also do it with xCustomListView using PreoptimizedCLV: https://www.b4x.com/android/forum/t...loading-extension-for-xcustomlistview.115289/

LucaMs · Mar 18, 2020

KZero said:
did you try to add 100,000 items with clv ?
clv is not suitable for such large numbers of items

I thought it was based on xCustomListView, since, at least with B4A, the normal ListView doesn't have Panels (or, perhaps better, doesn't expose them).

[or maybe your library isn't even based on ListView but written from scratch]

KZero · Mar 18, 2020

Erel said:
It is true that xCLV (currently) creates a panel for each item. With lazy loading you can create long lists.
One of the reasons that I don't think that it is a big issue is that a user will never scroll 100k items. This is not practical.

This library is made for those who find 250ms too slow to add only 1000 item to the list.

Erel · Mar 18, 2020

KZero said:
This library is made for those who find 250ms too slow to add only 1000 item to the list.

1. Don't get me wrong. It is good that there are more choices for developers and each developer will use whatever they find to be better for their requirements.
2. When I test it with xCLV adding 1000 items takes around 110ms on the first time and repeating it takes around 70ms. This is unnoticeable. It will be slower on slower devices, though 250ms is not really slow.

Edit: it takes 3ms to create 1000 items with xCLV and PreoptimizedCLV: https://www.b4x.com/android/forum/t...loading-extension-for-xcustomlistview.115289/

KZero · Mar 18, 2020

well,
few hundreds of milliseconds or even a few seconds may not matter if you are using a button to load the list
but when the list is loaded on the activity start it really matters

Mahares · Mar 18, 2020

Great work. You should change your name from KZero to KMillion:

B4X:

Sub btnAddItems_Click
    Dim ms As Long = DateTime.Now
    For i = 1 To 10000
        xLV.NewItem(180dip,i)
    Next
    xLV.Reload ' you must call reload after adding new items     
    lblTime.Text = "Load Time : " & (DateTime.Now - ms) & " ms    -   Total Items : " & xLV.Size 
    xLV.JumpToItem(xLV.Size-1)    '<--Did not jump to last item and error  when I added this line, but no crash 
End Sub

B4X:

Unexpected event (missing RaiseSynchronousEvents): xlv_panelrequested
Check the unfiltered logs for the full stack trace.

Also:
xLV.SetScrollbarColor(XUI.Color_Red) did not show the scroll bar

KZero · Mar 18, 2020

Mahares said:
xLV.JumpToItem(xLV.Size-1) '<--Did not jump to last item and error when I added this line, but no crash

JumpToItem works normally on all my devices and emulators, are you trying in Debug mode?
anyway try to add sleep(0) before calling jumpToItem or try to call it twice

B4X:

xLV.JumpToItem(xLV.Size-1)
sleep(0)
xLV.JumpToItem(xLV.Size-1)

Mahares said:
xLV.SetScrollbarColor(XUI.Color_Red) did not show the scroll bar

SetScrollbarColor may not work on all devices as mentioned here

Scrollbar Color

This code uses reflection to change the ScrollView scroll bar color: Sub SetScrollbarColor(sv As ScrollView, clr As Int) Dim r As Reflector r.Target = sv r.Target = r.GetField("mScrollCache") r.Target = r.GetField("scrollBar") Dim cd As ColorDrawable cd.Initialize(clr...

www.b4x.com

Mahares · Mar 18, 2020

KZero said:
try to add sleep(0) before calling jumpToItem

Thank you KMillion: This worked even in debug:

B4X:

Dim ms As Long = DateTime.Now
    For i = 1 To 10000
        xLV.NewItem(180dip,i)
    Next
    xLV.Reload ' you must call reload after adding new items 
    Sleep(0)  '<--- where it needs to be
    xLV.JumpToItem(xLV.Size-1)
    lblTime.Text = "Load Time : " & (DateTime.Now - ms) & " ms    -   Total Items : " & xLV.Size

Peter Simpson · Mar 19, 2020

Erel said:
It is true that xCLV (currently)<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<

Currently???
Are you thinking about changing it up a bit @Erel???

Erel · Mar 19, 2020

Peter Simpson said:
Are you thinking about changing it up a bit @Erel???

An option to add items without creating a panel might be added at some point, however lets keep this thread about xListView.

peacemaker · Mar 19, 2020

Such solution (of any list view) gives a warranty that no app crash at user's side when (and if) he collected so long list of needed items. Sure, it's stupid to scroll whole 100K list, but for the first time to "show all" - it's safe solution.
There are many real databases of any kind of goods that initially are very long: Aliexpress goods, auto spare-parts, flowers... any kind of items aggregator.
So - many thanks for such views.

XbNnX_507 · Mar 19, 2020

Does it support dynamic Height of panels ? how ?

KZero · Mar 20, 2020

XbNnX_507 said:
Does it support dynamic Height of panels ? how ?

now you can, download the latest update in the first post "v0.9" and example

peacemaker · Mar 20, 2020

KZero said:
"v0.9"

Works good even ... with 1.000.000 items 0.7 sec for adding each 1.000.000 items

Xfood · Sep 16, 2022

congratulations @KZero , it would be nice to have this library in B4x lib, so that you can use it for all B4x platforms

B4A Library xListview

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