If you’d rather not create this yourself, another option is to try 3rd party ListBox or DataView controls which have this built-in. Now this is just a quick example ( download here) and doesn’t handle every situation, but you can certainly expand on it as needed. Use the scrollbar to display other rows and you’ll see they are also displayed instantly even thought they are not technically in the ListBox. It will show the first bunch of rows instantly. Now click the second button that does the lazy loading. Another thing to note is that this uses about 750MB of RAM. You can scroll around at a reasonable speed, although it’s a bit unwieldy with that many rows. Click the first button to see how long it takes to populate the ListBox. Lastly add the ValueChanged event to the ScrollBar with this code, which fetches 50 rows after the value of the ScrollBar: Listbox1.RemoveAllRowsįor i As Integer = Me.Value To Me.Value + 50 ScrollBar1.MaximumValue = Data.LastRowIndex Now in the 2nd Button’s Action event add this code, which populates the ListBox only with the first 50 rows: Listbox1.RemoveAllRows Listbox1.AddRow(Data(i).Num.ToString, Data(i).Value.ToString, Data(i).Desc) In the Action event of the 1st Button, add this code to load the entire 1 million element array into the ListBox: Listbox1.HasVerticalScrollbar = Trueįor i As Integer = 0 To Data.LastRowIndex In the Open event of the Window add 1 million elements to the Data array: For i As Integer = 1 To 1000000 Change the ListBox to have 3 columns using the Column Count property in the Inspector. Align the ScrollBar so that it is to the right of the ListBox and the same height and change its Allow Live Scrolling property to True (ON). If ListBox1.RowCount < 0 Then Return Dim sValor As Currency Dim sTotal As Currency Dim rows As Integer ListBox1.RowCount-1 For i As Integer 0 To rows If ListBox1.Selected(i) Then sValor Val(ListBox1.Cell(i, 3) // Use the loop counter ListIndex is the last selected row sTotal sTotal + sValor End If End If TxtTotal. Now on Window1, add two Buttons, a Vertical Scroll Bar and a ListBox. On Window1, add a property that is an array of this class: Data() As ListData The class structure is like this: Class ListData To demonstrate this, start by creating a simple class as a container for data. One way to do this is to use a ScrollBar to track the data the user wants to see and then to only load that data into the ListBox. So why not only load the data they can actually see? This is often a great idea because the user can’t actually see all the data at once anyway. One way to avoid this problem is to not actually load all the data at once. It can take noticeable amount of time to to populate and you end up with your data being duplicated because it exists in both the ListBox and the original source (file, database or other data structure). But the ListBox, being a UI control, is not meant to also be a container for hundreds of thousands of rows of data. The ListBox is a great control for showing users lists of data, even data with lots and lots of rows.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |