C#

int taskIndex = listBoxTasks.IndexFromPoint(e.Location);

if (taskIndex > -1) // Check if there's an item under the cursor.
{
    Task currentTask = ((Task)bindingSourceTasks[taskIndex]); // Get the current item.

    if (currentTask != lastTask) // Check if it's not the same like before.
    {
        if (tooltip != null) // Check if tooltip is already open.
        {
            tooltip.Close();
        }

        tooltip = new frmTooltipComponent(currentTask); // Open new tooltip.
        tooltip.Show(); // Show tooltip;
        this.Focus(); // Set focus back to main window.
        tooltip.Top = Cursor.Position.Y; // Set tooltip Y-position.
        tooltip.Left = Cursor.Position.X + 50; // Set tooltip X-position.
        lastTask = currentTask;  // Remember current item.
    }
    else // If same item like before just set new tooltip position.
    {
        tooltip.Top = Cursor.Position.Y; // Set tooltip X-position.
        tooltip.Left = Cursor.Position.X + 50; // Remember current item.
    }
}
else if (tooltip != null) // If no hovered item check if tooltip is open.
{
    tooltip.Close(); // Close tooltip.
    lastTask = null; // Clear last remembered item.
}