loadingbar.xaml

<Window x:Class="WPFTestApp.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WPFTestApp"
        mc:Ignorable="d"
        Title="MainWindow" Height="350" Width="525">
    <Window.Resources>
        <Color x:Key="backgroundcolor" R="00" G="00" B="00" />
        <Color x:Key="foregroundcolor" R="0xFF" G="0xFF" B="0xFF" />
        <LinearGradientBrush x:Key="gradientBrush">
            <GradientStop x:Name="Stop1" Color="{StaticResource backgroundcolor}" Offset="-.4" />
            <GradientStop x:Name="Stop2" Color="{StaticResource foregroundcolor}" Offset="-.3" />
            <GradientStop x:Name="Stop3" Color="{StaticResource backgroundcolor}" Offset="-.2" />
            <GradientStop x:Name="Stop4" Color="{StaticResource foregroundcolor}" Offset="-.1" />
            <GradientStop x:Name="Stop5" Color="{StaticResource backgroundcolor}" Offset="0" />
            <GradientStop x:Name="Stop6" Color="{StaticResource foregroundcolor}" Offset=".1" />
            <GradientStop x:Name="Stop7" Color="{StaticResource backgroundcolor}" Offset=".2" />
            <GradientStop x:Name="Stop8" Color="{StaticResource foregroundcolor}" Offset=".3" />
            <GradientStop x:Name="Stop9" Color="{StaticResource backgroundcolor}" Offset=".4" />
            <GradientStop x:Name="Stop10" Color="{StaticResource foregroundcolor}" Offset=".5" />
            <GradientStop x:Name="Stop11" Color="{StaticResource backgroundcolor}" Offset=".6" />
            <GradientStop x:Name="Stop12" Color="{StaticResource foregroundcolor}" Offset=".7" />
            <GradientStop x:Name="Stop13" Color="{StaticResource backgroundcolor}" Offset=".8" />
            <GradientStop x:Name="Stop14" Color="{StaticResource foregroundcolor}" Offset=".9" />
            <GradientStop x:Name="Stop15" Color="{StaticResource backgroundcolor}" Offset="1.0" />
            <GradientStop x:Name="Stop16" Color="{StaticResource foregroundcolor}" Offset="1.1" />
            <GradientStop x:Name="Stop17" Color="{StaticResource backgroundcolor}" Offset="1.2" />
        </LinearGradientBrush>

        <Style x:Key="stripes" TargetType="Border">
            <Style.Triggers>
                <EventTrigger RoutedEvent="Loaded">
                    <BeginStoryboard>
                        <Storyboard>


                            <DoubleAnimation
                                            Storyboard.TargetProperty="gradientBrush.(GradientBrush.GradientStops)[1].(GradientStop.Offset)" 
                                            By=".2" Duration="0:0:1"
                                             RepeatBehavior="Forever"
                                            />
                            <DoubleAnimation
                                            Storyboard.TargetProperty="gradientBrush.(GradientBrush.GradientStops)[2].(GradientStop.Offset)" 
                                            By=".2" Duration="0:0:1"
                                             RepeatBehavior="Forever"
                                            />
                            <DoubleAnimation
                                            Storyboard.TargetProperty="gradientBrush.(GradientBrush.GradientStops)[3].(GradientStop.Offset)" 
                                            By=".2" Duration="0:0:1"
                                             RepeatBehavior="Forever"
                                            />
                            <DoubleAnimation
                                            Storyboard.TargetProperty="gradientBrush.(GradientBrush.GradientStops)[4].(GradientStop.Offset)" 
                                            By=".2" Duration="0:0:1"
                                             RepeatBehavior="Forever"
                                            />
                            <DoubleAnimation
                                            Storyboard.TargetProperty="gradientBrush.(GradientBrush.GradientStops)[5].(GradientStop.Offset)" 
                                            By=".2" Duration="0:0:1"
                                             RepeatBehavior="Forever"
                                            />
                            <DoubleAnimation
                                            Storyboard.TargetProperty="gradientBrush.(GradientBrush.GradientStops)[6].(GradientStop.Offset)" 
                                            By=".2" Duration="0:0:1"
                                             RepeatBehavior="Forever"
                                            />
                            <DoubleAnimation
                                            Storyboard.TargetProperty="gradientBrush.(GradientBrush.GradientStops)[7].(GradientStop.Offset)" 
                                            By=".2" Duration="0:0:1"
                                             RepeatBehavior="Forever"
                                            />
                            <DoubleAnimation
                                            Storyboard.TargetProperty="gradientBrush.(GradientBrush.GradientStops)[8].(GradientStop.Offset)" 
                                            By=".2" Duration="0:0:1"
                                             RepeatBehavior="Forever"
                                            />
                            <DoubleAnimation
                                            Storyboard.TargetProperty="gradientBrush.(GradientBrush.GradientStops)[9].(GradientStop.Offset)" 
                                            By=".2" Duration="0:0:1"
                                             RepeatBehavior="Forever"
                                            />
                            <DoubleAnimation
                                            Storyboard.TargetProperty="gradientBrush.(GradientBrush.GradientStops)[10].(GradientStop.Offset)" 
                                            By=".2" Duration="0:0:1"
                                             RepeatBehavior="Forever"
                                            />
                            <DoubleAnimation
                                            Storyboard.TargetProperty="gradientBrush.(GradientBrush.GradientStops)[11].(GradientStop.Offset)" 
                                            By=".2" Duration="0:0:1"
                                             RepeatBehavior="Forever"
                                            />
                            <DoubleAnimation
                                            Storyboard.TargetProperty="gradientBrush.(GradientBrush.GradientStops)[12].(GradientStop.Offset)" 
                                            By=".2" Duration="0:0:1"
                                             RepeatBehavior="Forever"
                                            />
                            <DoubleAnimation
                                            Storyboard.TargetProperty="gradientBrush.(GradientBrush.GradientStops)[13].(GradientStop.Offset)" 
                                            By=".2" Duration="0:0:1"
                                             RepeatBehavior="Forever"
                                            />
                            <DoubleAnimation
                                            Storyboard.TargetProperty="gradientBrush.(GradientBrush.GradientStops)[14].(GradientStop.Offset)" 
                                            By=".2" Duration="0:0:1"
                                             RepeatBehavior="Forever"
                                            />
                            <DoubleAnimation
                                            Storyboard.TargetProperty="gradientBrush.(GradientBrush.GradientStops)[15].(GradientStop.Offset)" 
                                            By=".2" Duration="0:0:1"
                                             RepeatBehavior="Forever"
                                            />


                        </Storyboard>
                    </BeginStoryboard>
                </EventTrigger>
            </Style.Triggers>
        </Style>
    </Window.Resources>
    <Grid Name="root">
        <Border BorderThickness="2" BorderBrush="Gray" Height="20" Width="150" Style="{StaticResource stripes}" />
    </Grid>
</Window>