自定义控件开发6---TypeConvert（类似编辑坐标）

  public   class  MyTypeConvert :ExpandableObjectConverter
    {
         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 ( string )  ||   base .CanConvertFrom(context, destinationType));
        }
         public   override   object  ConvertFrom(ITypeDescriptorContext context, System.Globalization.CultureInfo culture,
             object  value)
        {
             string  str  =  value  as   string ;
             if  (str  ==   null )
            {
                 return   base .ConvertFrom(context, culture, value);
            }
             string  str2  =  str.Trim();
             if  (str2.Length  ==   0 )  return   null ;
             if  (culture  ==   null ) culture  =  CultureInfo.CurrentCulture;
             char  ch  =  culture.TextInfo.ListSeparator[ 0 ];
             string [] strArray  =  str2.Split( new   char [] { ch });
             int [] numArray  =   new   int [strArray.Length];
            TypeConverter converter  =  TypeDescriptor.GetConverter( typeof ( int ));
             for  ( int  i  =   0 ; i  <  numArray.Length; i ++ )
            {
                numArray[i]  =  ( int )converter.ConvertFromString(context, culture, strArray[i]);
            }
             if  (numArray.Length  !=   3 )
            {
                 throw   new  Exception( " 格式不正确! " );
            }
             return   new  SolidCoordinate(numArray[ 0 ], numArray[ 1 ], numArray[ 2 ]);
        }
         public   override   object  ConvertTo(ITypeDescriptorContext context, System.Globalization.CultureInfo culture,  object  value, Type destinationType)
        {
             if  (destinationType  ==   null )
            {
                 throw   new  Exception( " 目标类型不能为空! " );
            }
             if  (value  is  SolidCoordinate)
            {
                 if  (destinationType  ==   typeof ( string ))
                {
                    SolidCoordinate solidCoordinate  =  (SolidCoordinate)value;
                     if  (culture  ==   null )
                    {
                        culture  =  CultureInfo.CurrentCulture;
                    }  string  separator  =  culture.TextInfo.ListSeparator  +   "   " ;
                    TypeConverter converter  =  TypeDescriptor.GetConverter( typeof ( int ));
                     string [] strArray  =   new   string [ 3 ];
                     int  num  =   0 ;
                    strArray[num ++ ]  =  converter.ConvertToString(context, culture,
                    solidCoordinate.X);
                    strArray[num ++ ]  =  converter.ConvertToString(context, culture,
                    solidCoordinate.Y);
                    strArray[num ++ ]  =  converter.ConvertToString(context, culture,
                    solidCoordinate.Z);
                     return   string .Join(separator, strArray);
                } 
                 if  (destinationType  ==   typeof (InstanceDescriptor))
                {
                    SolidCoordinate solidCoordinate2  =  (SolidCoordinate)value;
                    ConstructorInfo constructor  =   typeof (SolidCoordinate).
                    GetConstructor( new  Type[] {  typeof ( int ),  typeof ( int ),  typeof ( int ) });
                     if  (constructor  !=   null )
                    {
                         return   new  InstanceDescriptor(constructor,  new   object [] { solidCoordinate2.X, solidCoordinate2.Y, solidCoordinate2.Z });
                    }
                }
            } 
             return   base .ConvertTo(context, culture, value, destinationType);
        }
         public   override   object  CreateInstance(ITypeDescriptorContext context, System.Collections.IDictionary propertyValues)
        {
             if  (propertyValues  ==   null )
            {
                 throw   new  Exception( " 属性值不能为空! " );
            } 
             object  obj2  =  propertyValues[ " X " ];
             object  obj3  =  propertyValues[ " Y " ];
             object  obj4  =  propertyValues[ " Z " ];
             if  (((obj2  ==   null )  ||  (obj3  ==   null )  ||  (obj4  ==   null ))  ||  ( ! (obj2  is   int )  ||   ! (obj3  is   int )  ||   ! (obj4  is   int )))
            {
                 throw   new  Exception( " 格式不正确! " );
            }
             return   new  SolidCoordinate(( int )obj2, ( int )obj3, ( int )obj4);
        }
         public   override   bool  GetCreateInstanceSupported(ITypeDescriptorContext context)
        {
             return   true ;
        }
         // public override PropertyDescriptorCollection GetProperties(ITypeDescriptorContext context, object value, 
         //     Attribute[] attributes)
         // {
         //     return TypeDescriptor.GetProperties(typeof(SolidCoordinate), attributes).Sort(new string[] { "X", "Y", "Z" });
         // }
    }

从上面的代码中,我们看到override ConvertTo()方法时,当没有判断DestinationType 是否是InstanceDescriptor时, 当我们将控件拖入页面编辑属性，

再次编译时就会抛出'Unable to generate code for a value of type 'MyControls.Positions'. This error occurred while trying to generate the property value for MyPositions.'

为什呢？那是因为TypeConvertor必须从string转换成目标类型(ConvertFrom)或转换成string类型(TypeConvertor.ConvertTo).并且同时需要转换成InstanceDescriptior.

  if  (destinationType  ==   typeof (InstanceDescriptor))
                {
                    Positions obj2  =  value  as  Positions;
                    ConstructorInfo constructor  =   typeof (Positions).GetConstructor(
                         new  Type[] {  typeof ( int ),  typeof ( int ),  typeof ( int ) });
                     if  (constructor  !=   null )
                         return   new  InstanceDescriptor(constructor,
                             new   object [] { obj2.X, obj2.Y, obj2.Z });
                }

更多详细解释.http://weblogs.asp.net/bleroy/archive/2005/04/28/405013.aspx

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