WPF - hiding listbox items

This can also be achieved by populating ListBox.Items only with ListBoxItem instead of other controls:

ListBox.Items.Add(new ListBoxItem { 
    Content = new CheckBox {Content = "item 1"} 
    })

or

<ListBox>
    <ListBox.Items>
        <ListBoxItem>
            <CheckBox Content="item 1"/>
        </ListBoxItem>
    </ListBox.Items>
</ListBox>

Then in the code behind or in the trigger, you can hide the items directly:

ListBox.Items[0].Visibility = Visibility.Collapse

This will hide the item as well as the 4px border. This method gives you control of visibility for each individual item.

You are succesfully hiding your item, however, the ListBox wraps each of your items within a ListBoxItem, this adds concepts such as selection to your item. I suspect you are still seeing the ListBoxItem in the case where your items are hidden. You can use the ItemContainerStyle to hide ListBoxItems ...

<ListBox>
  <ListBox.ItemContainerStyle>
    <Style TargetType="{x:Type ListBoxItem}">
      <Style.Triggers>
        <DataTrigger Binding="{Binding IsActive}" Value="False">
          <Setter Property="Visibility" Value="Collapsed"/>
        </DataTrigger>
      </Style.Triggers>
    </Style>
  </ListBox.ItemContainerStyle>
</ListBox>