Why is my UI object moving slightly below the actual goal?

Question

I am making an UWP project, and while I was browsing through my settings app on windows, I realised there is a blue line moving whenever I press a button. I wanted to remake it in UWP for my project, because it looks good. But whenever the animation plays, it moves a couple of 100 epx below the actual button.

Why?

Xaml script:

<Page
    x:Class="Library.Views.MainMenuView"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:Library.Helpers"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    Background="{ThemeResource ApplicationBackgroundBrush}">

    <Grid>
        <Border HorizontalAlignment="Left" MaxWidth="400" MinWidth="200" Width="Auto" Height="Auto" Background="{ThemeResource ControlBackgroundBrush}" BorderBrush="{ThemeResource ControlHoveredBorderBrush}" BorderThickness="1" CornerRadius="0,8,8,0" >
            <StackPanel x:Name="Buttons">
                    <Button x:Name="Home" Style="{StaticResource UIButtonStyle}" Width="300" Height="40" FontSize="20" HorizontalAlignment="Center" Margin="5,8,12,8" Click="Button_Click">
                        <StackPanel Orientation="Horizontal" VerticalAlignment="Center">
                            <Image Source="/Assets/HomeNoBGRes.png" Width="35" Height="30" Margin ="0,0,10,0" Stretch="Fill"/>
                            <TextBlock Text="Home" FontSize="20" Width="240"/>
                        </StackPanel>
                    </Button>
                    <Button x:Name="Projects" Style="{StaticResource UIButtonStyle}" Width="300" Height="40" FontSize="20" HorizontalAlignment="Center" Margin="5,8,12,8" Click="Button_Click">
                        <StackPanel Orientation="Horizontal" VerticalAlignment="Center">
                            <Image Source="/Assets/ProjectsNoBGRes.png" Width="30" Height="30" Margin ="0,0,10,0" Stretch="Fill"/>
                            <TextBlock Text="My Projects" FontSize="20" Width="240"/>
                        </StackPanel>
                    </Button>
                    <Border Background="{ThemeResource ControlHoveredBackgroundBrush}" Width="270" Height="5" CornerRadius="3" HorizontalAlignment="Center"/>
                    <Button x:Name="Documents" Style="{StaticResource UIButtonStyle}" Width="300" Height="40" FontSize="20" HorizontalAlignment="Center" Margin="5,8,12,8" Click="Button_Click">
                        <StackPanel Orientation="Horizontal" VerticalAlignment="Center">
                            <Image Source="/Assets/DocsNoBGRes.png" Width="30" Height="30" Margin ="0,0,10,0" Stretch="Fill"/>
                            <TextBlock Text="Documents" FontSize="20" Width="240"/>
                        </StackPanel>
                    </Button>
                    <Button x:Name="Paper" Style="{StaticResource UIButtonStyle}" Width="300" Height="40" FontSize="20" HorizontalAlignment="Center" Margin="5,8,12,8" Click="Button_Click">
                        <StackPanel Orientation="Horizontal" VerticalAlignment="Center">
                            <Image Source="/Assets/PaperNoBGRes.png" Width="30" Height="30" Margin ="0,0,10,0" Stretch="Fill"/>
                            <TextBlock Text="Paper" FontSize="20" Width="240"/>
                        </StackPanel>
                    </Button>
                </StackPanel>
        </Border>
        <Border x:Name="SelectionIndicator" Visibility="Collapsed" Background="{ThemeResource SystemAccentColor}" Height="30" Width="5" CornerRadius="3" HorizontalAlignment="Left" Margin="5,0,0,0"/>
    </Grid>
</Page>

and the C# animating function:

        private void Button_Click(object sender, RoutedEventArgs e)
        {
            if (SelectionIndicator.Visibility == Visibility.Collapsed) SelectionIndicator.Visibility = Visibility.Visible;

            if (sender is  Button clickedButton) 
            { 
                double indicatorLeft = clickedButton.TransformToVisual(Buttons).TransformPoint(new Point(0, 0)).Y;

                if (SelectionIndicator.RenderTransform is null || !(SelectionIndicator.RenderTransform is CompositeTransform)) SelectionIndicator.RenderTransform = new CompositeTransform();

                CompositeTransform transform = SelectionIndicator.RenderTransform as CompositeTransform;

                Storyboard storyboard = new Storyboard();
                DoubleAnimation moveAnimation = new DoubleAnimation
                {
                    To = indicatorLeft,
                    Duration = TimeSpan.FromSeconds(0.5),
                    EnableDependentAnimation = true,
                    EasingFunction = new CircleEase { EasingMode= EasingMode.EaseInOut },
                };

                Storyboard.SetTarget(moveAnimation, transform);
                Storyboard.SetTargetProperty(moveAnimation, "TranslateY");

                storyboard.Children.Add(moveAnimation);

                storyboard.Begin();
            }
        }

Here is a picture showcasing my problem:

I tried adding a grid to the border because maybe it was caused because they weren't in the same container, but no.

Thanks in advance!

(To moderators: don't remove my thanks in advances, these are meant to thank the people who actually help me)

Answer 1

The reason for this behavior is that the SelectionIndicator is centered on the left by default, and its position can be seen after setting Visibility="Visible".

It is recommended to add VerticalAlignment="Top" in SelectionIndicator. and use StackPanel with Orientation="Horizontal".

The following is my test code, with some styles deleted.

<Grid>
  <StackPanel Orientation="Horizontal">
      
      <Border x:Name="SelectionIndicator" Visibility="Collapsed" Background="{ThemeResource SystemAccentColor}" Height="40" Width="5" CornerRadius="3" HorizontalAlignment="Left" VerticalAlignment="Top" Margin="5,0,0,0"/>
      
      <Border HorizontalAlignment="Left" MaxWidth="400" MinWidth="200" Width="Auto" Height="Auto" BorderThickness="1" CornerRadius="0,8,8,0" >
          <StackPanel x:Name="Buttons">
              <Button x:Name="Home" Width="300" Height="40" FontSize="20" HorizontalAlignment="Center" Margin="5,8,12,8" Click="Button_Click">
                  <StackPanel Orientation="Horizontal" VerticalAlignment="Center">
                      <Image Source="/Assets/HomeNoBGRes.png" Width="35" Height="30" Margin ="0,0,10,0" Stretch="Fill"/>
                      <TextBlock Text="Home" FontSize="20" Width="240"/>
                  </StackPanel>
              </Button>
              <Button x:Name="Projects"  Width="300" Height="40" FontSize="20" HorizontalAlignment="Center" Margin="5,8,12,8" Click="Button_Click">
                  <StackPanel Orientation="Horizontal" VerticalAlignment="Center">
                      <Image Source="/Assets/ProjectsNoBGRes.png" Width="30" Height="30" Margin ="0,0,10,0" Stretch="Fill"/>
                      <TextBlock Text="My Projects" FontSize="20" Width="240"/>
                  </StackPanel>
              </Button>
              <Border Width="270" Height="5" CornerRadius="3" HorizontalAlignment="Center"/>
              <Button x:Name="Documents"  Width="300" Height="40" FontSize="20" HorizontalAlignment="Center" Margin="5,8,12,8" Click="Button_Click">
                  <StackPanel Orientation="Horizontal" VerticalAlignment="Center">
                      <Image Source="/Assets/DocsNoBGRes.png" Width="30" Height="30" Margin ="0,0,10,0" Stretch="Fill"/>
                      <TextBlock Text="Documents" FontSize="20" Width="240"/>
                  </StackPanel>
              </Button>
              <Button x:Name="Paper" Width="300" Height="40" FontSize="20" HorizontalAlignment="Center" Margin="5,8,12,8" Click="Button_Click">
                  <StackPanel Orientation="Horizontal" VerticalAlignment="Center">
                      <Image Source="/Assets/PaperNoBGRes.png" Width="30" Height="30" Margin ="0,0,10,0" Stretch="Fill"/>
                      <TextBlock Text="Paper" FontSize="20" Width="240"/>
                  </StackPanel>
              </Button>
          </StackPanel>
      </Border>
      
  </StackPanel>