ListView slow and max width

ListView becomes slow when it contains many columns, even if only a few of them are displayed. Here is a sample code that illustrates the issue. When you try to scroll it, it takes a long time to repaint. Virtual mode does not help. I am not really sure why it takes so long to paint 120 cells.

Private ListView1 As New ListView With {.Size = New Size(300, 400)}

Private Sub Form1_Load(sender As Object, e As EventArgs) Handles Me.Load
    Const columns = 600
    Controls.Add(ListView1)

    With ListView1
        .BeginUpdate()
        .View = View.Details
        .HeaderStyle = ColumnHeaderStyle.Nonclickable

        For c = 1 To columns
            .Columns.Add(c.ToString, 50, HorizontalAlignment.Center)
        Next

        For r = 1 To 20
            Dim l As New ListViewItem(r & "1")
            For c = 2 To columns
                l.SubItems.Add(r & c)
            Next
            .Items.Add(l)
        Next
        .EndUpdate()
    End With
End Sub

Another issue I found is that it looks like there is a limitation of how large the width of all columns can be, i. e. in my sample code you can change the column count to 700 and observe how the last columns will not be visible. The last ones that will be visible will not allow you to change their width.

[r-aghaei]

@riov For the columns rendering, the behavior is the same in .NET Framework. For the scroll/repaint I couldn’t see any problem. For the resize issue, I believe it’s a limitation in the Windows message. Consider WM_MOUSEMOVE, the lParam parameter determines the mouse position. The low-order word specifies the x-coordinate and the high-order word specifies the y-coordinate of the cursor. Using 16 bit for x and 16 bit for y means it can not handle coordinates larger that 32767. That’s why if you create a lot of columns, for the right most columns (which their x-coordinate is larger that 32767) you cannot change the column size, the column even do not get highlighted by mouse. If you take a look at WM_MOUSEMOVE message using spy++, you will see negative x-coordinate for them.

[RussKie]

Anyway, I would like to suggest two new features:

Could you please raise separate issues for each one, thank you. Because both of these suggestions affect public API we’ll need to have an assessment how these changes will affect existing consumers.

It remains a mystery to me, why ListsView cannot show the same performance.

Not sure, it could be an underlying limitation of Win32 API… A Windows Explorer struggles to scroll when one has beyond certain number of files in a folder too.