wpf-notifyicon/Source/Sample Project/Tutorials/02 - ToolTips/UserControlToolTipWindow.xaml

<Window
    x:Class="Samples.Tutorials.ToolTips.UserControlToolTipWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:tb="http://www.hardcodet.net/taskbar"
    xmlns:local="clr-namespace:Samples.Tutorials.ToolTips"
    Height="300"
    Width="300">
    <Grid>

        <tb:TaskbarIcon
            x:Name="MyNotifyIcon"
            IconSource="/Icons/Error.ico"
            ToolTipText="hello world">

            <!-- assign user control as ToolTip -->
            <tb:TaskbarIcon.TrayToolTip>
                <local:SimpleUserControl />
            </tb:TaskbarIcon.TrayToolTip>

        </tb:TaskbarIcon>
        <TextBlock Margin="26,26,24,0" VerticalAlignment="Top" FontWeight="Bold" TextWrapping="Wrap">
            <Run Text="Move mouse over NotifyIcon to show ToolTip" Language="de-ch" />
        </TextBlock>

    </Grid>
</Window>