WPF Border Width change in smooth mode via DoubleAnimation of MVVM and implemented via C#, monitor moderate change via CompositionTarget.Rendering event

private void Init()
{
    var tempBorder = win.FindName("border") as Border;
    if (tempBorder != null)
    {
        border = tempBorder;
    }
    if (widthAnimation==null)
    {
        widthAnimation = new DoubleAnimation();
        widthAnimation.From = shortWidth;
        widthAnimation.To = longWidth;
        widthAnimation.AutoReverse = true;
        widthAnimation.RepeatBehavior = RepeatBehavior.Forever;
        widthAnimation.Duration = TimeSpan.FromSeconds(3);
        border.BeginAnimation(FrameworkElement.WidthProperty, widthAnimation);
    }
}



private void CompositionTarget_Rendering(object? sender, EventArgs e)
{
    TitleStr = border?.ActualWidth.ToString();
    System.Diagnostics.Debug.WriteLine(TitleStr);
}

 

 

 

 

 

 

 

 

 

//xaml
<Window x:Class="WpfApp18.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:WpfApp18"
        WindowState="Maximized"
        mc:Ignorable="d"
        Title="{Binding TitleStr,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}"
        Height="450" Width="800">
    <Grid>
        <Border x:Name="border"
                  Background="Red"
                  Height="500"
                  Width="{Binding BorderWidth,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}"
                  BorderBrush="Blue"
                  BorderThickness="10"
                  HorizontalAlignment="Center"
                  VerticalAlignment="Center"/>
    </Grid>
</Window>



//cs
using System.ComponentModel;
using System.Runtime.CompilerServices;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace WpfApp18
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            var vm = new MainVM(this);
            this.DataContext = vm;
        }
    }

    public class MainVM : INotifyPropertyChanged
    {
        private Window win;
        private Border border;
        private double longWidth = 0;
        private double shortWidth = 100;
        private DoubleAnimation widthAnimation;

        public MainVM(Window winValue)
        {
            win= winValue;
            if(win!=null)
            {
                win.Loaded += Win_Loaded;                
                CompositionTarget.Rendering += CompositionTarget_Rendering;
            }
        }

        private void CompositionTarget_Rendering(object? sender, EventArgs e)
        {
            TitleStr = border?.ActualWidth.ToString();
            System.Diagnostics.Debug.WriteLine(TitleStr);
        }

        private void Win_Loaded(object sender, RoutedEventArgs e)
        {
            longWidth = win.ActualWidth;
            Init();
        }

        private void Init()
        {
            var tempBorder = win.FindName("border") as Border;
            if (tempBorder != null)
            {
                border = tempBorder;
            }
            if (widthAnimation==null)
            {
                widthAnimation = new DoubleAnimation();
                widthAnimation.From = shortWidth;
                widthAnimation.To = longWidth;
                widthAnimation.AutoReverse = true;
                widthAnimation.RepeatBehavior = RepeatBehavior.Forever;
                widthAnimation.Duration = TimeSpan.FromSeconds(3);
                border.BeginAnimation(FrameworkElement.WidthProperty, widthAnimation);
            }
        }

        public event PropertyChangedEventHandler? PropertyChanged;
        public void OnPropertyChanged([CallerMemberName] string propertyName = "")
        {
            var handler = PropertyChanged;
            if (handler != null)
            {
                handler?.Invoke(this, new PropertyChangedEventArgs(propertyName));
            }
        }

        private string titleStr;
        public string TitleStr
        {
            get
            {
                return titleStr;
            }
            set
            {
                if(value!=titleStr)
                {
                    titleStr = value;
                    OnPropertyChanged();
                }
            }
        }

        private double borderWidth;
        public double BorderWidth
        {
            get
            {
                return borderWidth;
            }
            set
            {
                if (value != borderWidth)
                {
                    borderWidth = value;
                    OnPropertyChanged();
                }
            }
        }
    }
}