我对自定义TypeConverter的布尔属性有问题.如果我有这个课程：

public class MyClass {
    public string Name { get; set; }

    [System.ComponentModel.TypeConverter( typeof( BoolTypeConverter ) )]
    public bool Flag { get; set; }
}

我在PropertyGrid中创建实例并将其设置为SelectedObject – 一切正常,直到用户在属性网格项上的DoubleClicked形成“Flag”属性. DoubleClick提出此消息后：alt text http://tcks.wz.cz/property_grid_error.PNG

TypeConverter类看起来：

public class BoolTypeConverter : System.ComponentModel.TypeConverter {
    public const string TEXT_TRUE = "On";
    public const string TEXT_FALSE = "Off";
    public const string TEXT_NONE = "< none >";

    public override object CreateInstance( System.ComponentModel.ITypeDescriptorContext context,System.Collections.IDictionary propertyValues ) {
        object ret = base.CreateInstance( context,propertyValues );
        return ret;
    }
    public override bool GetCreateInstanceSupported( System.ComponentModel.ITypeDescriptorContext context ) {
        bool ret = base.GetCreateInstanceSupported( context );
        return ret;
    }
    public override bool IsValid( System.ComponentModel.ITypeDescriptorContext context,object value ) {
        bool ret;
        if ( value is string ) {
            string tmpValue = value.ToString().Trim();

            if ( string.Compare( tmpValue,TEXT_NONE,StringComparison.InvariantCultureIgnoreCase ) == 0 ) {
                ret = true;
            }
            else if ( string.Compare( tmpValue,TEXT_TRUE,TEXT_FALSE,StringComparison.InvariantCultureIgnoreCase ) == 0 ) {
                ret = true;
            }
            else {
                bool blValue;
                ret = bool.TryParse( tmpValue,out blValue );
            }
        }
        else {
            ret = base.IsValid( context,value );
        }

        return ret;
    }

    public override bool CanConvertFrom( System.ComponentModel.ITypeDescriptorContext context,Type sourceType ) {
        bool ret = false;
        if ( sourceType == typeof( string ) ) {
            ret = true;
        }
        else {
            ret = base.CanConvertFrom( context,sourceType );
        }

        return ret;
    }
    public override object ConvertFrom( System.ComponentModel.ITypeDescriptorContext context,System.Globalization.CultureInfo culture,object value ) {
        object ret = null;

        bool converted = false;
        if ( value is string ) {
            string tmpValue = value.ToString().Trim();
            if ( string.Compare( tmpValue,StringComparison.InvariantCultureIgnoreCase ) == 0
                || string.IsNullOrEmpty( tmpValue ) ) {
                ret = null;
                converted = true;
            }
            else if ( string.Compare( tmpValue,StringComparison.InvariantCultureIgnoreCase ) == 0 ) {
                ret = true;
                converted = true;
            }
            else if ( string.Compare( tmpValue,StringComparison.InvariantCultureIgnoreCase ) == 0 ) {
                ret = false;
                converted = true;
            }
            else {
                bool blValue;
                if ( converted = bool.TryParse( tmpValue,out blValue ) ) {
                    ret = blValue;
                }
            }
        }

        if ( false == converted ) {
            ret = base.ConvertFrom( context,culture,value );
        }
        return ret;
    }

    public override bool CanConvertTo( System.ComponentModel.ITypeDescriptorContext context,Type destinationType ) {
        bool ret = false;
        if ( destinationType == typeof( bool ) ) {
            ret = true;
        }
        else {
            ret = base.CanConvertTo( context,destinationType );
        }

        return ret;
    }
    public override object ConvertTo( System.ComponentModel.ITypeDescriptorContext context,object value,Type destinationType ) {
        object ret = null;

        bool converted = false;
        if ( destinationType == typeof( string ) ) {
            if ( null == value ) {
                ret = TEXT_NONE;
                converted = true;
            }
            else if ( value is bool? || value is bool ) {
                if ( (bool)value ) { ret = TEXT_TRUE; }
                else { ret = TEXT_FALSE; }

                converted = true;
            }
            else if ( value is string ) {
                ret = value;
                converted = true;
            }
        }
        if ( false == converted ) {
            ret = base.ConvertTo( context,value,destinationType );
        }
        return ret;
    }

    public override StandardValuesCollection GetStandardValues( System.ComponentModel.ITypeDescriptorContext context ) {
        StandardValuesCollection ret;
        Type tpProperty = context.PropertyDescriptor.PropertyType;
        if ( tpProperty == typeof( bool ) ) {
            ret = new StandardValuesCollection( new string[]{
            TEXT_TRUE,TEXT_FALSE
        } );
        }
        else if ( tpProperty == typeof( bool? ) ) {
            ret = new StandardValuesCollection( new string[]{
                TEXT_TRUE,TEXT_NONE
            } );
        }
        else {
            ret = new StandardValuesCollection( new string[0] );
        }

        return ret;
    }
    public override bool GetStandardValuesSupported( System.ComponentModel.ITypeDescriptorContext context ) {
        bool ret;
        Type tpProperty = context.PropertyDescriptor.PropertyType;
        if ( tpProperty == typeof( bool ) || tpProperty == typeof( bool? ) ) {
            ret = true;
        }
        else {
            ret = false;
        }

        return ret;
    }
}

这种行为对用户来说非常混乱.我该怎样预防呢？

谢谢