Select Listbox 中的所有项目，通过 BackgroundWorker 将它们全部添加到 Listview

Question

I am having some problems lately with selecting ALL items( ONLY once.) from a listbox and adding them to a listview. I am using a backgroundworker to handle this task due to big content the listview will contain and to avoid GUI freezing while performing this task.

Ok, so here is the BackgroundWorker_ProgressChanged code:

  For Each item In ListBox3.SelectedItems

    listView1.Items.Add(ListBox3.SelectedItem, ImageList1.Images.Count - 1).SubItems.Add("Test")
      ListView1.Items("Test").SubItems.Add("")
       Next
      For Each item As ListViewItem In ListView1.SelectedItems

      Next
     End Sub

The above written code displays items in listview, but ONLY if the user selects a certain item from the Listbox3 and displays infinite times the selected items from the listbox, I want it display ONLY ONCE all selected items from the Listbox, in the Listview. I want to select ALL items automatically, without user intervention, I have tried several methods which have failed. Can someone please provide a solution to this issue? Thanks.

Answer 1

I just tested and it seems that getting items from a ListBox on a secondary thread is not an issue, so I was wrong about that. Adding/setting items definitely would be though, so you'd need to add the items to the ListView on the UI thread. Here's some example code that just worked for me:

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    BackgroundWorker1.RunWorkerAsync()
End Sub

Private Sub BackgroundWorker1_DoWork(sender As Object, e As DoWorkEventArgs) Handles BackgroundWorker1.DoWork
    Dim outputItems As New List(Of ListViewItem)

    For Each inputItem As String In ListBox1.Items
        outputItems.Add(New ListViewItem(inputItem))
    Next

    e.Result = outputItems
End Sub

Private Sub BackgroundWorker1_RunWorkerCompleted(sender As Object, e As RunWorkerCompletedEventArgs) Handles BackgroundWorker1.RunWorkerCompleted
    Dim items = DirectCast(e.Result, List(Of ListViewItem))

    ListView1.Items.AddRange(items.ToArray())
End Sub

Answer 2

The problem is all the screen redrawing. I am guessing you may not need a background worker if you limit the screen redraw.

I used a list for the ListViewItems since I don't know how many there will be. Had to convert the list to an array to use .AddRange .

As a matter of fact just the .BeginUpdate and .EndUpdate might speed things up enough to be acceptable.

I am not sure about the use of ImageList so you might have to play around with that.

Private Sub OpCode()
    Dim items = From itm In ListBox1.Items 'or ListBox1.SelectedItems
                Select CStr(itm)
    Dim lvItems As New List(Of ListViewItem)
    Dim imageIndex As Integer = ImageList1.Images.Count - 1
    For Each item In items
        Dim lvItem As New ListViewItem(item, imageIndex)
        lvItems.Add(lvItem)
    Next
    'ListView1.BeginUpdate()
    ListView1.Items.AddRange(lvItems.ToArray)
    'ListView1.EndUpdate()
End Sub