This is a part of my Code Snippets collection, needed in many projects. There are many cases, where xCustomListView is the best way to show a list of data.
The data I like to load into a list of a self defined type as first step from a file, a database or a server/cloud. Only from there as second step data will be shown in the CustomListView. Here the user can see, edit, delete or add data and in the end, the new data will be saved to file/database or uploaded to server/cloud. See also Using SQLite.
If there are hundreds or thousands of items, Lazy Loading is a better way. We create empty items and only the area on the display is loaded.
The data I like to load into a list of a self defined type as first step from a file, a database or a server/cloud. Only from there as second step data will be shown in the CustomListView. Here the user can see, edit, delete or add data and in the end, the new data will be saved to file/database or uploaded to server/cloud. See also Using SQLite.
Filling a list from SQLite database:
Sub Class_Globals
Type PersonType(ID As Int, Name As String, age as Short)
End Sub
'This example returns a persons list from database with an age filter
Private Sub GetPersons() As List
Dim rs As ResultSet
rs = SQL1.ExecQuery("SELECT * FROM Person WHERE [age] BETWEEN 18 AND 35")
Dim li As List : li.Initialize
Do While rs.NextRow
li.Add(CreatePersonType(rs.GetInt("ID"), rs.GetString("Name"), rs.GetInt("age")))
Loop
rs.Close
Return li
End Sub
'you can create this Sub moving the mouse cursor over Type definition
Private Sub CreatePersonType(ID As Int, Name As String, age as Short)
Dim t As PersonType : t.Initialize
t.ID = ID
t.Name = Name
t.age = age
return t
End Sub
Showing this list in CustomListView:
Private Sub ShowPersons()
dim li as List = GetPersons()
clvPersons.Clear
dim iWidth as int = clvPersons.AsView.Width, iHeight as int = 60dip 'look in the created layout for .Top and .Height values of the views, to calculate the Item-Height that is needed!
For Each t As PersonType In li
clvPersons.Add(CreatePersonItem(t, iWidth, iHeight), t)
Next
End Sub
Private Sub CreatePersonItem(t as PersonType, width As Int, height As Int) As B4XView
Dim p As B4XView = xui.CreatePanel("")
p.SetLayoutAnimated(0, 0, 0, width, height)
p.LoadLayout("viewItmPerson") 'Create a layout "viewItmPerson" in designer with Labels "lblItmName" and "lblItmAge"
lblItmName.Text = t.name
lblItmAge.Text = t.age
Return p
End Sub
Private Sub clvPersons_ItemClick (Index As Int, Value As Object)
dim t as PersonType = Value
'do something with the user choice ...
End SubIf there are hundreds or thousands of items, Lazy Loading is a better way. We create empty items and only the area on the display is loaded.
Showing list with Lazy Loading:
Sub BuildListItems(li As List)
Dim iWidth As Int = clvPersons.AsView.Width, iHeight As Int = 60dip
clvPersons.Clear
For Each t As PersonType In li
Dim Pnl As B4XView = xui.CreatePanel(Null) 'Create a new B4X View
Pnl.Color = xui.Color_White 'Set the background color to white
Pnl.SetLayoutAnimated(0dip, 0dip, 0dip, iWidth, iHeight) 'Set the list position and dimensions
clvPersons.Add(Pnl, t)
Next
End Sub
'POPULATE THE XCUSTOMLISTVIEW WITH THE BUILT ITEMS CREATED IN THE SUB ABOVE
Sub clvPersons_VisibleRangeChanged (FirstIndex As Int, LastIndex As Int) 'LL, Lazy Loading
If FirstIndex > 0 And FirstIndex = LastIndex Then Return
Dim ExtraSize As Int = 25 'Add 25 items at a time, this can be changed to suite your requirements
For i = Max(0, FirstIndex - ExtraSize) To Min(LastIndex + ExtraSize, clvItems.Size - 1) 'Loop for adding/removing your items layout to or from the list
Dim Pnl As B4XView = clvPersons.GetPanel(i) 'Declare a new B4XView
If i > FirstIndex - ExtraSize And i < LastIndex + ExtraSize Then 'Add a new item to the list
If Pnl.NumberOfViews = 0 Then 'Add items to the list
Dim t As PersonType = clvPersons.GetValue(i) 'Get your custom Type
End If
Else 'Remove items from the list
If Pnl.NumberOfViews > 0 Then
Pnl.RemoveAllViews 'Remove none visible item from the main xCLV layout
End If
End If
Next
End Sub
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