class GifImage : Image
    {
        private bool _isInitialized;
        private GifBitmapDecoder _gifDecoder;
        private Int32Animation _animation;

        public int FrameIndex
        {
            get { return (int)GetValue(FrameIndexProperty); }
            set { SetValue(FrameIndexProperty, value); }
        }

        
 
private void Initialize()
        {
            _gifDecoder = new GifBitmapDecoder(new Uri((this.GifSource.StartsWith("pack://") ? "" : "pack://application:,,,") + this.GifSource), BitmapCreateOptions.PreservePixelFormat, BitmapCacheOption.Default);
            var frameinfo = _gifDecoder.Metadata.GetFrameInfo();
            
 
var delay = frameinfo.Delay;
            _animation = new Int32Animation(0, _gifDecoder.Frames.Count - 1, new Duration(new TimeSpan(0, 0, 0, delay.Seconds * _gifDecoder.Frames.Count + (delay.Milliseconds * _gifDecoder.Frames.Count) / 1000, (delay.Milliseconds * _gifDecoder.Frames.Count) % 1000)));
            _animation.RepeatBehavior 
 
= RepeatBehavior.Forever;
            this.Source = _gifDecoder.Frames[0];

            _isInitialized = true;
        }

        static GifImage()
        {
            VisibilityProperty.OverrideMetadata(typeof(GifImage),
                new FrameworkPropertyMetadata(VisibilityPropertyChanged));
        }

        private static void VisibilityPropertyChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
        {
            if ((Visibility)e.NewValue == Visibility.Visible)
            {
                ((GifImage)sender).StartAnimation();
            }
            else
            {
                ((GifImage)sender).StopAnimation();
            }
        }

        public static readonly DependencyProperty FrameIndexProperty =
            DependencyProperty.Register("FrameIndex", typeof(int), typeof(GifImage), new UIPropertyMetadata(0, new PropertyChangedCallback(ChangingFrameIndex)));

        static void ChangingFrameIndex(DependencyObject obj, DependencyPropertyChangedEventArgs ev)
        {
            var gifImage = obj as GifImage;
            gifImage.Source = gifImage._gifDecoder.Frames[(int)ev.NewValue];
        }

        /// <summary>
        /// Defines whether the animation starts on it's own
        /// </summary>
        public bool AutoStart
        {
            get { return (bool)GetValue(AutoStartProperty); }
            set { SetValue(AutoStartProperty, value); }
        }

        public static readonly DependencyProperty AutoStartProperty =
            DependencyProperty.Register("AutoStart", typeof(bool), typeof(GifImage), new UIPropertyMetadata(false, AutoStartPropertyChanged));

        private static void AutoStartPropertyChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
        {
            if ((bool)e.NewValue)
                (sender as GifImage).StartAnimation();
        }

        public string GifSource
        {
            get { return (string)GetValue(GifSourceProperty); }
            set { SetValue(GifSourceProperty, value); }
        }

        public static readonly DependencyProperty GifSourceProperty =
            DependencyProperty.Register("GifSource", typeof(string), typeof(GifImage), new UIPropertyMetadata(string.Empty, GifSourcePropertyChanged));

        private static void GifSourcePropertyChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
        {
            (sender as GifImage).Initialize();
        }

        /// <summary>
        /// Starts the animation
        /// </summary>
        public void StartAnimation()
        {
            if (!_isInitialized)
                this.Initialize();

            BeginAnimation(FrameIndexProperty, _animation);
        }

        /// <summary>
        /// Stops the animation
        /// </summary>
        public void StopAnimation()
        {
            BeginAnimation(FrameIndexProperty, null);
        }
    }

enum FrameDisposalMethod
    {
        Replace = 0,
        Combine = 1,
        RestoreBackground = 2,
        RestorePrevious = 3
    }

 class FrameInfo
    {
        /// <summary>
        /// 兩個圖片的時間
        /// </summary>
        public TimeSpan Delay { get; set; }
        /// <summary>
        /// 圖片是如何顯示
        /// </summary>
        public FrameDisposalMethod DisposalMethod { get; set; }
        public double Width { get; set; }
        public double Height { get; set; }
        public double Left { get; set; }
        public double Top { get; set; }

        public Rect Rect
        {
            get { return new Rect(Left, Top, Width, Height); }
        }
    }

static class BitmapMetadataMethod
    {

        public static FrameInfo GetFrameInfo(this BitmapMetadata metadata)
        {
            var frameInfo = new FrameInfo
            {
                Delay = TimeSpan.FromMilliseconds(100),
                DisposalMethod = FrameDisposalMethod.Replace,
                Width = 0,
                Height = 0,
                Left = 0,
                Top = 0
            };

            try
            {
                if (metadata != null)
                {
                    const string delayQuery = "/grctlext/Delay";
                    const string disposalQuery = "/grctlext/Disposal";
                    const string widthQuery = "/imgdesc/Width";
                    const string heightQuery = "/imgdesc/Height";
                    const string leftQuery = "/imgdesc/Left";
                    const string topQuery = "/imgdesc/Top";

                    var delay = metadata.GetQueryOrNull<ushort>(delayQuery);
                    if (delay.HasValue)
                        frameInfo.Delay = TimeSpan.FromMilliseconds(10 * delay.Value);

                    var disposal = metadata.GetQueryOrNull<byte>(disposalQuery);
                    if (disposal.HasValue)
                        frameInfo.DisposalMethod = (FrameDisposalMethod)disposal.Value;

                    var width = metadata.GetQueryOrNull<ushort>(widthQuery);
                    if (width.HasValue)
                        frameInfo.Width = width.Value;

                    var height = metadata.GetQueryOrNull<ushort>(heightQuery);
                    if (height.HasValue)
                        frameInfo.Height = height.Value;

                    var left = metadata.GetQueryOrNull<ushort>(leftQuery);
                    if (left.HasValue)
                        frameInfo.Left = left.Value;

                    var top = metadata.GetQueryOrNull<ushort>(topQuery);
                    if (top.HasValue)
                        frameInfo.Top = top.Value;
                }
            }
            catch (NotSupportedException)
            {
            }

            return frameInfo;
        }
        public static T? GetQueryOrNull<T>(this BitmapMetadata metadata, string query)
                where T : struct
        {
            if (metadata.ContainsQuery(query))
            {
                object value = metadata.GetQuery(query);
                if (value != null)
                    return (T)value;
            }
            return null;
        }
    }

前端使用：

 <local:GifImage x:Name="gifImage" Width="400" Height="300" Stretch="UniformToFill"  GifSource="pack://application:,,,/FamilyParamReader;Component/Image/loading.gif" AutoStart="True" />

不知道是不是我圖片問題，迴圈播放的時候，起始的位置總會有閃一下。不知道怎麼解決。

參考文章：

https://blog.csdn.net/weixin_30628077/article/details/97698859

https://thomaslevesque.com/2011/03/27/wpf-display-an-animated-gif-image/

https://stackoverflow.com/questions/210922/how-do-i-get-an-animated-gif-to-work-in-wpf