Question

Here is the problem: I have a Windows Forms application that I’m developing, and in one segment I’m using a ListView control.

What I’m trying can be simply stated as: on event ListViewItemSelectionChange show a MessageBox for user to confirm the change, if not confirmed change to let’s say the first item. This change to the first item would again fire ListViewItemSelecionChange, so I unregister and re-register the event handler method, so everything should be good, right?

What actually happens is that the handler method is called twice (actually ListView should fire two events on Selection change, one for deselect, other for newly selected item, but I have an e.IsSelected statement at the beginning to catch only selected items, so actually you could say that there are four events fired).

The problem is, if I generated the first event with mouse click on ListView item, and I’ve unsubscribed before programatically changing to the first item, what generates the second event firing? Is it some focus change because of the MessageBox call? Is there any way to prevent the second event to fire?

I have a simple example solution here, it can’t be more simlified (25 SLOC), so if you can, please take a look. Note that commenting the line “if (ShowMessageBox())” stops the second event from firing, is this some focus change problem?

http://www.filedropper.com/listviewtestwithmsgbox

Edit: the relevant code:

private void listViewWithSelection1_ItemSelectionChanged(object sender, ListViewItemSelectionChangedEventArgs e)
{
    // listview actually generates two ItemSelectionChanged events,
    // one for deselect of a item, and another event for a newly selected item (which we want here).
    if (e.IsSelected)
    {
        if (ShowMessageBox())
            Button1_Click(null, EventArgs.Empty);

        label1.Text += "item selected   ";
    }
}

private bool ShowMessageBox()
{
    return MessageBox.Show("Change to first item instead?", "test", MessageBoxButtons.YesNo) == DialogResult.Yes;
}

private void Button1_Click(object sender, EventArgs e)
{
    // change ti first ListView item
    listView1.ItemSelectionChanged -= listViewWithSelection1_ItemSelectionChanged;
    listView1.Items[0].Selected = true;
    listView1.ItemSelectionChanged += listViewWithSelection1_ItemSelectionChanged;
}

Answer 1

Hmm, can you describe how the selection is being changed to begin with? If it’s by the user clicking to select an item, perhaps catch the Click or DoubleClick event rather than the ItemSelectionChanged event? I have this snippet I’m using on a program currently. If the user double clicks the list box (listView, in your case), do something with the selected item.

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
    }

    private bool ShowMessageBox()
    {
        return MessageBox.Show("Change to first item instead?", "test", MessageBoxButtons.YesNo) == DialogResult.Yes;
    }

    private void listView1_Click(object sender, EventArgs e)
    {
        if (ShowMessageBox())
            listView1.TopItem.Selected = true;
            label1.Text += "item selected   ";
    }
}

Edited to include relevant code.