Inserting elements in a ListView

In this section, you can see how to change the getAdd() stub with code that let you insert a bulk of elements into a ListView.

Description

Certain code patterns in VB6 to insert a massive amount of elements in a ListView may present a performance gap in .NET when the code is converted. This entry covers that situation and how it can be fixed manually.

Inserting elements

In VB6 it is common to find a loop, like a do-while, iterating over a list of elements and inserting them into a ListView. Let's consider the following example:

Private Sub Form_Load()
    Dim ss(6) As String
    ss(1) = "this"
    ss(2) = "is"
    ss(3) = "a"
    ss(4) = "sample"
    ss(5) = "of"
    ss(6) = "code"
    
    Dim lv As ListItem
    k = 1
    Do While k < 7
        Set lv = Me.ListView1.ListItems.Add
        lv.Text = ss(k)
        k = k + 1
    Loop
End Sub

When converted, that code will look like:

private void Form_Load()
		{
			string[] ss = new string[]{"", "", "", "", "", "", ""};
			ss[1] = "this";
			ss[2] = "is";
			ss[3] = "a";
			ss[4] = "sample";
			ss[5] = "of";
			ss[6] = "code";

			ListViewItem lv = null;
			int k = 1;

			while(k < 7)
			{
				//UPGRADE_ISSUE: (2064) MSComctlLib.IListItems method ListView1.ListItems.Add was not upgraded.
				lv = this.ListView1.Items.getAdd();
				lv.Text = ss[k];
				k++;
			};
		}

Besides the manual change to overcome the getAdd() stub, that can be replaced by something like:

lv = new ListViewItem();
listView1.Items.Add(lv);

However, inserting one ListViewItem at a time can take a lot of time in .NET. Instead of this way of adding elements, consider inserting a bulk of elements at once:

private void Form_Load()
		{
			string[] ss = new string[]{"", "", "", "", "", "", ""};
			ss[1] = "this";
			ss[2] = "is";
			ss[3] = "a";
			ss[4] = "sample";
			ss[5] = "of";
			ss[6] = "code";

			List<ListViewItem> items = new List<ListViewItem>();
			ListViewItem lv = new ListViewItem();
			
			int k = 1;

			while(k < 7)
			{
				lv = new ListViewItem();
				items.Add(lv);
				lv.Text = ss[k];
				k++;
			};
			listView1.Items.AddRange(items.ToArray());
		}

The above while-loop insert elements into a typed List of ListViewItem and then, after the while, the ListView.AddRange() method is used to insert the bulk of items.