support for .NET framework 3.5

Still have bugs

Net35/HandyControl_Net35/Data/Gif/GifImageInfo.cs

@@ -0,0 +1,97 @@
+using System;
+using HandyControl.Controls;
+
+namespace HandyControl.Data
+{
+    public class GifImageInfo
+    {
+        private const int PropertyTagFrameDelay = 0x5100;
+
+        private int _frame;
+
+        private readonly int[] _frameDelay;
+
+        public int FrameCount { get; }
+
+        internal GifImage Image { get; }
+
+        public bool Animated { get; }
+
+        public EventHandler FrameChangedHandler { get; set; }
+
+        internal int FrameTimer { get; set; }
+
+        public bool FrameDirty { get; private set; }
+
+        public int Frame
+        {
+            get => _frame;
+            set
+            {
+                if (_frame != value)
+                {
+                    if (value < 0 || value >= FrameCount)
+                    {
+                        throw new ArgumentException("InvalidFrame");
+                    }
+
+                    if (Animated)
+                    {
+                        _frame = value;
+                        FrameDirty = true;
+
+                        OnFrameChanged(EventArgs.Empty);
+                    }
+                }
+            }
+        }
+
+        public GifImageInfo(GifImage image)
+        {
+            Image = image;
+            Animated = ImageAnimator.CanAnimate(image);
+
+            if (Animated)
+            {
+                FrameCount = image.GetFrameCount(GifFrameDimension.Time);
+
+                var frameDelayItem = image.GetPropertyItem(PropertyTagFrameDelay);
+
+                // If the image does not have a frame delay, we just return 0.                                     
+                //
+                if (frameDelayItem != null)
+                {
+                    // Convert the frame delay from byte[] to int
+                    //
+                    var values = frameDelayItem.Value;
+                    _frameDelay = new int[FrameCount];
+                    for (int i = 0; i < FrameCount; ++i)
+                    {
+                        _frameDelay[i] = values[i * 4] + 256 * values[i * 4 + 1] + 256 * 256 * values[i * 4 + 2] + 256 * 256 * 256 * values[i * 4 + 3];
+                    }
+                }
+            }
+            else
+            {
+                FrameCount = 1;
+            }
+            if (_frameDelay == null)
+            {
+                _frameDelay = new int[FrameCount];
+            }
+        }
+
+        public int FrameDelay(int frame) => _frameDelay[frame];
+
+        internal void UpdateFrame()
+        {
+            if (FrameDirty)
+            {
+                Image.SelectActiveFrame(GifFrameDimension.Time, Frame);
+                FrameDirty = false;
+            }
+        }
+
+        protected void OnFrameChanged(EventArgs e) => FrameChangedHandler?.Invoke(Image, e);
+    }
+}