类型转换：自定义属性中带有复杂类型（如IMAGE）该如何实现？

Question

自己创建了个类用于收纳控件属性，这个类带有个Image类型的字段，但在使用的时候，字符串等类型数据都能成功记录设计时设置，Image就不可以，该如何解决？代码如下：
    /// <summary>
    /// Banner内容信息类
    /// </summary>
    [TypeConverter(typeof(BannerContentInfoConverter))]
    public sealed class BannerContentInfo
    {
        private string _caption = "标题";
        /// <summary>
        /// 获取或设置Banner标题
        /// </summary>
        [Category("Appearance"), DefaultValue("标题"), Description("设置Banner标题")]
        public string Caption
        {
            get
            {
                return _caption;
            }
            set
            {
                if (value == null)
                {
                    value = "";
                }
                if (value != this._caption)
                {
                    this._caption = value;
                    this.EnsureInvalidate(false);
                }
            }
        }        private string _description = "";
        /// <summary>
        /// 获取或设置Banner说明
        /// </summary>
        [Category("Appearance"), DefaultValue(""), Description("设置Banner说明")]
        public string Description
        {
            get
            {
                return _description;
            }
            set
            {
                if (value == null)
                {
                    value = "";
                }
                if (value != this._description)
                {
                    _description = value;
                    this.EnsureInvalidate(false);
                }
            }
        }        private Image _glyph = null;
        /// <summary>
        /// 获取或设置Banner图标
        /// </summary>
        [Category("Appearance"), DefaultValue((string)null), Description("设置Banner图标")]
        public Image Glyph
        {
            get
            {
                return this._glyph;
            }
            set
            {
                if (_glyph != null)
                {
                    this._glyph = value;
                    this.EnsureInvalidate(false);
                }
            }
        }        /// <summary>
        /// 获取Banner内容的文字形式
        /// </summary>
        /// <returns></returns>
        public override string ToString()
        {
            return string.Format(CultureInfo.CurrentCulture, "[{0}: Caption={1}, Description={2}, Units={3}, GdiCharSet={4}, GdiVerticalFont={5}]", new object[] { base.GetType().Name, this.Caption, this.Description});//, (int)this.fontUnit, this.gdiCharSet, this.gdiVerticalFont });
        }
    }

Answer 1

下面的是 类型转换器代码：    internal class BannerContentInfoConverter : TypeConverter
    {
        private const string DataHdr = "data=";        public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
        {
            return ((sourceType == typeof(string)) || base.CanConvertFrom(context, sourceType));
        }        public override bool CanConvertTo(ITypeDescriptorContext context, Type destinationType)
        {
            return ((destinationType == typeof(InstanceDescriptor)) || base.CanConvertTo(context, destinationType));
        }        public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)
        {
            if (value is string)
            {
                string text = (value as string).Trim();
                if (text.Length == 0)
                {
                    return new BannerContentInfo();
                }
                if (culture == null)
                {
                    culture = CultureInfo.CurrentCulture;
                }
                string separator = culture.TextInfo.ListSeparator + " " + DataHdr;
                string[] datas = text.Split(new string[] { separator }, StringSplitOptions.None);
                if (datas.Length < 2 || datas.Length > 3)
                {
                    throw new ArgumentException("1|" + separator + "|" + value.ToString());
                }
                string caption = datas[0];
                string description = datas[1];
                Image glyph = null;
                if(datas.Length == 3)
                {
                    try
                    {
                        byte[] glyphData = Convert.FromBase64String(datas[2]);
                        TypeConverter convert = TypeDescriptor.GetConverter(typeof(Image));
                        if (convert != null)
                        {
                            glyph = convert.ConvertFrom(glyphData) as Image;
                        }
                    }
                    catch
                    {
                    }
                }
                return new BannerContentInfo() { Caption = caption, Description = description, Glyph = glyph };
            }
            if (value is BannerContentInfo)
            {
                BannerContentInfo content = value as BannerContentInfo;
                return new BannerContentInfo() { Caption = content.Caption, Description = content.Description, Glyph = content.Glyph };
            }
            return base.ConvertFrom(context, culture, value);
        }        public override object ConvertTo(ITypeDescriptorContext context, CultureInfo culture, object value, Type destinationType)
        {
            if (destinationType == null)
            {
                throw new ArgumentNullException("destinationType");
            }
            if (destinationType == typeof(string))
            {
                BannerContentInfo content = value as BannerContentInfo;
                if (content == null)
                {
                    return "toStringNone";
                }
                if (culture == null)
                {
                    culture = CultureInfo.CurrentCulture;
                }
                string separator = culture.TextInfo.ListSeparator + " " + DataHdr;
                int count = 2;
                if (content.Glyph != null)
                {
                    count++;
                }
                string[] datas = new string[count];
                int index = 0;
                datas[index++] = content.Caption;
                datas[index++] = content.Description;
                if (content.Glyph != null)
                {
                    TypeConverter convert = TypeDescriptor.GetConverter(typeof(Image));
                    byte[] glyph = convert.ConvertTo(content.Glyph, typeof(byte[])) as byte[];
                    datas[index++] = Convert.ToBase64String(glyph);
                }
                return string.Join(separator, datas);
            }
            if ((destinationType == typeof(InstanceDescriptor)) && (value is BannerContentInfo))
            {
                BannerContentInfo content = (BannerContentInfo)value;
                return new BannerContentInfo() { Caption = content.Caption, Description = content.Description, Glyph = content.Glyph };
            }
            return base.ConvertTo(context, culture, value, destinationType);
        }        public override object CreateInstance(ITypeDescriptorContext context, IDictionary propertyValues)
        {
            if (propertyValues == null)
            {
                throw new ArgumentNullException("propertyValues");
            }
            string caption = propertyValues["Caption"] as string;
            string description = propertyValues["Description"] as string;
            Image glyph = propertyValues["Glyph"] as Image;
            return new BannerContentInfo() { Caption = caption, Description = description, Glyph = glyph };
        }        public override bool GetCreateInstanceSupported(ITypeDescriptorContext context)
        {
            return true;
        }        public override PropertyDescriptorCollection GetProperties(ITypeDescriptorContext context, object value, Attribute[] attributes)
        {
            return TypeDescriptor.GetProperties(typeof(BannerContentInfo), attributes).Sort(new string[] { "Caption", "Description", "Glyph" });
        }        public override bool GetPropertiesSupported(ITypeDescriptorContext context)
        {
            return true;
        }
    }

Answer 2

1、有错别字的原因:)        [Category("Appearance"), DefaultValue((string)null), Description("设置Banner图标")]
        public Image Glyph
        {
            get
            {
                return this._glyph;
            }
            set
            {
                //if (_glyph != null)
                if( value != null)                      //<------------
                {
                    this._glyph = value;
                    this.EnsureInvalidate(false);
                }
            }
        }

Answer 3

 private Image _glyph = null;
        /// <summary>
        /// 获取或设置Banner图标
        /// </summary>
        [Category("Appearance"), DefaultValue((string)null), Description("设置Banner图标")]
        public Image Glyph
        {
            get
            {
                return this._glyph;
            }
            set
            {
                if (_glyph != null)
                {
                    this._glyph = value;
                    this.EnsureInvalidate(false);
                }
            }
        }

Answer 4

2、我没有看出你的TypeConverter实际起了什么作用，不如不写，而是直接用ExpandableObjectConverter。
你TypeConverter中转换为InstanceDescriptor的实现有误
    class My : Component
    {
        BannerContentInfo bi = new BannerContentInfo();
        public BannerContentInfo BB { get { return bi; } set { bi = value; } }
    }    [TypeConverter(typeof(ExpandableObjectConverter))]             //<---
    public sealed class BannerContentInfo
    {
       //...
    }

Answer 5

 使用默认的EXPANDABLEOBJECTCONVERT类后，发现数据不能保存。

Answer 6

火了，开始都很好的，突然不能保存数据了，总说不能把 BannerContentInfo 转换为 TypeDescriptor。郁闷。

Answer 7

““BannerContentInfoConverter”无法将“Superdata.WebCAD.Common.UI.UIComponents.BannerContentInfo”转换为“System.ComponentModel.Design.Serialization.InstanceDescriptor”。”

Answer 8

通过一天的调试，终于发现，出现这个问题的原因是DLL被重新编译了，此时，IDE使用的类型以及类型转换DLL却跟目标代码使用的类型不一致，这些代码我都是放在一个模块的。假如IDE使用的设计时DLL能自动更新就好了。每次修改都要重新打开VSIDE，还是有点烦。