support for .NET framework 3.5

Still have bugs

Net35/HandyControl_Net35/Data/Gif/GifPropertyItemInternal.cs

@@ -0,0 +1,114 @@
+using System;
+using System.Runtime.InteropServices;
+using HandyControl.Tools;
+
+namespace HandyControl.Data
+{
+    [StructLayout(LayoutKind.Sequential)]
+    public class GifPropertyItemInternal : IDisposable
+    {
+        public int id;
+        public int len;
+        public short type;
+        public IntPtr value = IntPtr.Zero;
+
+        internal GifPropertyItemInternal()
+        {
+        }
+
+        public byte[] Value
+        {
+            get
+            {
+                if (len == 0)
+                    return null;
+
+                var bytes = new byte[len];
+
+                Marshal.Copy(value,
+                    bytes,
+                    0,
+                    len);
+                return bytes;
+            }
+        }
+
+        public void Dispose()
+        {
+            Dispose(true);
+        }
+
+        ~GifPropertyItemInternal()
+        {
+            Dispose(false);
+        }
+
+        private void Dispose(bool disposing)
+        {
+            if (value != IntPtr.Zero)
+            {
+                Marshal.FreeHGlobal(value);
+                value = IntPtr.Zero;
+            }
+
+            if (disposing)
+                GC.SuppressFinalize(this);
+        }
+
+        internal static GifPropertyItemInternal ConvertFromPropertyItem(GifPropertyItem propItem)
+        {
+            var propItemInternal = new GifPropertyItemInternal
+            {
+                id = propItem.Id,
+                len = 0,
+                type = propItem.Type
+            };
+
+            var propItemValue = propItem.Value;
+            if (propItemValue != null)
+            {
+                var length = propItemValue.Length;
+                propItemInternal.len = length;
+                propItemInternal.value = Marshal.AllocHGlobal(length);
+                Marshal.Copy(propItemValue, 0, propItemInternal.value, length);
+            }
+
+            return propItemInternal;
+        }
+
+        internal static GifPropertyItem[] ConvertFromMemory(IntPtr propdata, int count)
+        {
+            var props = new GifPropertyItem[count];
+
+            for (var i = 0; i < count; i++)
+            {
+                GifPropertyItemInternal propcopy = null;
+                try
+                {
+                    propcopy = (GifPropertyItemInternal) ExternDllHelper.PtrToStructure(propdata,
+                        typeof(GifPropertyItemInternal));
+
+                    props[i] = new GifPropertyItem
+                    {
+                        Id = propcopy.id,
+                        Len = propcopy.len,
+                        Type = propcopy.type,
+                        Value = propcopy.Value
+                    };
+
+                    // this calls Marshal.Copy and creates a copy of the original memory into a byte array.
+
+                    propcopy.value = IntPtr.Zero; // we dont actually own this memory so dont free it.
+                }
+                finally
+                {
+                    propcopy?.Dispose();
+                }
+
+                propdata = (IntPtr) ((long) propdata + Marshal.SizeOf(typeof(GifPropertyItemInternal)));
+            }
+
+            return props;
+        }
+    }
+}