gistfile1.xml

<Window x:Class="AsyncWpf.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="*"></RowDefinition>
            <RowDefinition Height="auto"></RowDefinition>
        </Grid.RowDefinitions>
        <ListBox Name="output"></ListBox>
        <StackPanel Grid.Row="1" Orientation="Horizontal">
            <Button  Name="StartButton" Click="StartButtonClick">Start</Button>
            <Button  Name="StopButton" IsEnabled="False" Click="StopButtonClick">Stop</Button>
        </StackPanel>
    </Grid>
</Window>