C# TypeConverter.CanConvertFrom方法代碼示例

		public void CheckConvert(int expect_from, int expect_to, TypeConverter conv, Type type) {
			int from_count	 = 0;
			int to_count	 = 0;

			foreach (Type t in typeof(int).Assembly.GetTypes ()) {
				if (conv.CanConvertFrom(null, t)) {
					from_count++;
					if (debug > 0) {
						Console.WriteLine("{0}: Conversion from {1} supported", conv.ToString(), t.ToString());
					}
				}

				if (conv.CanConvertTo(null, t)) {
					to_count++;
					if (debug > 0) {
						Console.WriteLine("{0}: Conversion to {1} supported", conv.ToString(), t.ToString());
					}
				}
			}

#if not
			foreach (Type t in type.Assembly.GetTypes ()) {
				if (conv.CanConvertFrom(null, t)) {
					from_count++;
					if (debug > 0) {
						Console.WriteLine("{0}: Conversion from {1} supported", conv.ToString(), t.ToString());
					}
				}

				if (conv.CanConvertTo(null, t)) {
					to_count++;
					if (debug > 0) {
						Console.WriteLine("{0}: Conversion to {1} supported", conv.ToString(), t.ToString());
					}
				}
			}
#endif

			if (from_count != expect_from) {
				if (verbose > 0) {
					Console.WriteLine("{0}: ConvertFrom expected {1}, returned {2}", conv.ToString(), expect_from, from_count);
				}
				failed++;
			}

			if (to_count != expect_to) {
				if (verbose > 0) {
					Console.WriteLine("{0}: ConvertTo expected {1}, returned {2}", conv.ToString(), expect_to, to_count);
				}
				failed++;
			}

		}

        /// <summary>
        /// This method retrieves a set of CDSAttribute from a class.
        /// </summary>
        /// <param name="data">The class to examine.</param>
        /// <param name="conv">A converter function to turn the value in to a string.</param>
        /// <returns>Returns an enumerable collection of attributes and values.</returns>
        public static IEnumerable<KeyValuePair<CDSAttributeAttribute, string>> CDSAttributesRetrieve(
            this IXimuraContent data, TypeConverter conv)
        {
            List<KeyValuePair<PropertyInfo, CDSAttributeAttribute>> attrList =
                AH.GetPropertyAttributes<CDSAttributeAttribute>(data.GetType());

            foreach (KeyValuePair<PropertyInfo, CDSAttributeAttribute> reference in attrList)
            {
                PropertyInfo pi = reference.Key;

                if (pi.PropertyType == typeof(string))
                {
                    yield return new KeyValuePair<CDSAttributeAttribute, string>(
                        reference.Value, pi.GetValue(data, null) as string);
                }
                else if (pi.PropertyType == typeof(IEnumerable<string>))
                {
                    IEnumerable<string> enumerator = pi.GetValue(data, null) as IEnumerable<string>;
                    foreach (string value in enumerator)
                        yield return new KeyValuePair<CDSAttributeAttribute, string>(
                            reference.Value, value);
                }
                else if (conv != null && conv.CanConvertFrom(pi.PropertyType))
                {
                    yield return new KeyValuePair<CDSAttributeAttribute, string>(
                        reference.Value, conv.ConvertToString(pi.GetValue(data, null)));
                }
            }
        }

		private void SetValueFromConverter(string newValue, Type targetType, TypeConverter converter)
		{
			if (!converter.CanConvertFrom(targetType) && string.IsNullOrEmpty(newValue))
			{
				this.Value = null;
			}
			else
			{
				this.Value = converter.ConvertFrom(newValue);
			}
		}

        /// <devdoc>
        ///
        /// Converts a value into a format suitable for display to the end user.
        ///
        /// - Converts DBNull or null into a suitable formatted representation of 'null'
        /// - Performs some special-case conversions (eg. Boolean to CheckState)
        /// - Uses TypeConverters or IConvertible where appropriate
        /// - Throws a FormatException is no suitable conversion can be found
        ///
        /// </devdoc>
        private static object FormatObjectInternal(object value,
                                                   Type targetType, 
                                                   TypeConverter sourceConverter, 
                                                   TypeConverter targetConverter, 
                                                   string formatString, 
                                                   IFormatProvider formatInfo, 
                                                   object formattedNullValue) {
            if (value == System.DBNull.Value || value == null) {
                //
                // Convert DBNull to the formatted representation of 'null' (if possible)
                //
                if (formattedNullValue != null)
                {
                    return formattedNullValue;
                }

                //
                // Convert DBNull or null to a specific 'known' representation of null (otherwise fail)
                //
                if (targetType == stringType)
                {
                    return String.Empty;
                }
                
                if (targetType == checkStateType) {
                    return CheckState.Indeterminate;
                }
                
                // Just pass null through: if this is a value type, it's been unwrapped here, so we return null 
                // and the caller has to wrap if appropriate.
                return null; 
            }

            //
            // Special case conversions
            //

            if (targetType == stringType) {
                if (value is IFormattable && !String.IsNullOrEmpty(formatString)) {
                    return (value as IFormattable).ToString(formatString, formatInfo);
                }
            }

            //The converters for properties should take precedence.  Unfortunately, we don't know whether we have one.  Check vs. the 
            //type's TypeConverter.  We're punting the case where the property-provided converter is the same as the type's converter.
            Type sourceType = value.GetType();
            TypeConverter sourceTypeTypeConverter = TypeDescriptor.GetConverter(sourceType);
            if (sourceConverter != null && sourceConverter != sourceTypeTypeConverter && sourceConverter.CanConvertTo(targetType)) {
                return sourceConverter.ConvertTo(null, GetFormatterCulture(formatInfo), value, targetType);
            }

            TypeConverter targetTypeTypeConverter = TypeDescriptor.GetConverter(targetType);
            if (targetConverter != null && targetConverter != targetTypeTypeConverter && targetConverter.CanConvertFrom(sourceType)) {
                return targetConverter.ConvertFrom(null, GetFormatterCulture(formatInfo), value);
            }

            if (targetType == checkStateType) {
                if (sourceType == booleanType) {
                    return ((bool)value) ? CheckState.Checked : CheckState.Unchecked;
                } 
                else {
                    if (sourceConverter == null) {
                        sourceConverter = sourceTypeTypeConverter;
                    }
                    if (sourceConverter != null && sourceConverter.CanConvertTo(booleanType)) {
                        return (bool)sourceConverter.ConvertTo(null, GetFormatterCulture(formatInfo), value, booleanType)
                            ? CheckState.Checked : CheckState.Unchecked;
                    }
                }
            }

            if (targetType.IsAssignableFrom(sourceType)) {
                return value;
            }

            //
            // If explicit type converters not provided, supply default ones instead
            //

            if (sourceConverter == null) {
                sourceConverter = sourceTypeTypeConverter;
            }

            if (targetConverter == null) {
                targetConverter = targetTypeTypeConverter;
            }

            //
            // Standardized conversions
            //
//.........這裏部分代碼省略.........

        /// <devdoc>
        ///
        /// Converts a value entered by the end user (through UI) into the corresponding binary value.
        ///
        /// - Converts formatted representations of 'null' into DBNull
        /// - Performs some special-case conversions (eg. CheckState to Boolean)
        /// - Uses TypeConverters or IConvertible where appropriate
        /// - Throws a FormatException is no suitable conversion can be found
        ///
        /// </devdoc>
        private static object ParseObjectInternal(object value, 
                                                  Type targetType, 
                                                  Type sourceType, 
                                                  TypeConverter targetConverter, 
                                                  TypeConverter sourceConverter, 
                                                  IFormatProvider formatInfo, 
                                                  object formattedNullValue) {
            //
            // Convert the formatted representation of 'null' to DBNull (if possible)
            //

            if (EqualsFormattedNullValue(value, formattedNullValue, formatInfo) || value == System.DBNull.Value) {
                return System.DBNull.Value;
            }

            //
            // Special case conversions
            //

            TypeConverter targetTypeTypeConverter = TypeDescriptor.GetConverter(targetType);
            if (targetConverter != null && targetTypeTypeConverter != targetConverter && targetConverter.CanConvertFrom(sourceType)) {
                return targetConverter.ConvertFrom(null, GetFormatterCulture(formatInfo), value);
            }

            TypeConverter sourceTypeTypeConverter = TypeDescriptor.GetConverter(sourceType);
            if (sourceConverter != null && sourceTypeTypeConverter != sourceConverter && sourceConverter.CanConvertTo(targetType)) {
                return sourceConverter.ConvertTo(null, GetFormatterCulture(formatInfo), value, targetType);
            }

            if (value is string) {
                // If target type has a suitable Parse method, use that to parse strings
                object parseResult = InvokeStringParseMethod(value, targetType, formatInfo);
                if (parseResult != parseMethodNotFound) {
                    return parseResult;
                }
            }
            else if (value is CheckState) {
                CheckState state = (CheckState)value;
                if (state == CheckState.Indeterminate) {
                    return DBNull.Value;
                }
                // Explicit conversion from CheckState to Boolean
                if (targetType == booleanType) {
                    return (state == CheckState.Checked);
                }
                if (targetConverter == null) {
                    targetConverter = targetTypeTypeConverter;
                }
                if (targetConverter != null && targetConverter.CanConvertFrom(booleanType)) {
                    return targetConverter.ConvertFrom(null, GetFormatterCulture(formatInfo), state == CheckState.Checked);
                }
            }
            else if (value != null && targetType.IsAssignableFrom(value.GetType())) {
                // If value is already of a compatible type, just go ahead and use it
                return value;
            }

            //
            // If explicit type converters not provided, supply default ones instead
            //

            if (targetConverter == null) {
                targetConverter = targetTypeTypeConverter;
            }

            if (sourceConverter == null) {
                sourceConverter = sourceTypeTypeConverter;
            }

            //
            // Standardized conversions
            //

            if (targetConverter != null && targetConverter.CanConvertFrom(sourceType)) {
                return targetConverter.ConvertFrom(null, GetFormatterCulture(formatInfo), value);
            }
            else if (sourceConverter != null && sourceConverter.CanConvertTo(targetType)) {
                return sourceConverter.ConvertTo(null, GetFormatterCulture(formatInfo), value, targetType);
            }
            else if (value is IConvertible) {
                return ChangeType(value, targetType, formatInfo);
            }

            //
            // Fail if no suitable conversion found
            //

            throw new FormatException(GetCantConvertMessage(value, targetType));
        }

 internal static bool CanConvertToFrom(TypeConverter converter, Type type) {
     return (converter != null && converter.CanConvertTo(type) &&
             converter.CanConvertFrom(type) && !(converter is ReferenceConverter));
 }

		bool SafeCanConvertFrom (Type type, TypeConverter cvt)
		{
			try {
				return cvt.CanConvertFrom (type);
			} catch (NotImplementedException) {
				return false;
			}
		}

		object ConvertData (TypeConverter c)
		{
			if (mime_type == ResXResourceWriter.ByteArraySerializedObjectMimeType) {
				if (c.CanConvertFrom (typeof (byte [])))
					return c.ConvertFrom (Convert.FromBase64String (dataString));
			} else if (String.IsNullOrEmpty (mime_type)) {
				if (c.CanConvertFrom (typeof (string)))
					return c.ConvertFromInvariantString (dataString);
			}
			else
				throw new Exception ("shouldnt get here, invalid mime type");

			throw new TypeLoadException ("No converter for this type found");
		}

        /// <summary>
        /// This method retrieves a set of reference attributes from a class.
        /// </summary>
        /// <param name="data">The class to examine.</param>
        /// <param name="conv">A converter function to turn the value in to a string.</param>
        /// <returns>Returns an enumerable collection of attributes and values.</returns>
        public static IEnumerable<KeyValuePair<CDSReferenceAttribute, string>> CDSReferencesRetrieve(
            this IXimuraContent data, TypeConverter conv)
        {
            List<KeyValuePair<PropertyInfo, CDSReferenceAttribute>> attrList =
                AH.GetPropertyAttributes<CDSReferenceAttribute>(data.GetType());

            foreach (KeyValuePair<PropertyInfo, CDSReferenceAttribute> reference in attrList)
            {
                PropertyInfo pi = reference.Key;

                if (pi.PropertyType != typeof(string) &&
                    (conv == null || !conv.CanConvertFrom(pi.PropertyType)))
                    continue;

                string value;

                if (pi.PropertyType == typeof(string))
                    value = pi.GetValue(data, null) as string;
                else
                    value = conv.ConvertToString(pi.GetValue(data, null));

                yield return new KeyValuePair<CDSReferenceAttribute, string>(reference.Value, value);
            }
        }

 private static bool CanConvertToAndFromString(TypeConverter converter)
 {
     return converter.CanConvertFrom(typeof(string)) &&
            converter.CanConvertTo(typeof(string));
 }

      private static bool TryConvertTo( object value, Type targetType, CultureInfo culture, TypeConverter converter, out object result )
      {
        if( converter != null )
        {
          try
          {
            result = converter.ConvertTo( null, culture, value, targetType );
            return true;
          }
          catch
          {
            // We'll try to convert the value another way.
          }

          if( ( value != null ) && ( converter.CanConvertFrom( value.GetType() ) ) )
          {
            try
            {
              var newValue = converter.ConvertFrom( null, culture, value );
              result = converter.ConvertTo( null, culture, newValue, targetType );

              return true;
            }
            catch
            {
            }
          }
        }

        result = null;
        return false;
      }

        private void CreateConverter() {
            // Some properties cannot have type converters.
            // Such examples are properties that are ConfigurationElement ( derived classes )
            // or properties which are user-defined and the user code handles serialization/desirialization so
            // the property itself is never converted to/from string

            if (_converter == null) {
                // Enums are exception. We use our custom converter for all enums
                if (_type.IsEnum) {
                    _converter = new GenericEnumConverter(_type);
                }
                else if (!_type.IsSubclassOf(typeof(ConfigurationElement))) {
                    _converter = TypeDescriptor.GetConverter(_type);

                    if ((_converter == null) ||
                            !_converter.CanConvertFrom(typeof(String)) ||
                            !_converter.CanConvertTo(typeof(String))) {
                        throw new ConfigurationErrorsException(SR.GetString(SR.No_converter, _name, _type.Name));
                    }
                }
            }
        }

 private static bool ConvertObjectToTypeInternal(object o, Type type, JavaScriptSerializer serializer, bool throwOnError, out object convertedObject)
 {
     IDictionary<string, object> dictionary = o as IDictionary<string, object>;
     if (dictionary != null)
     {
         return ConvertDictionaryToObject(dictionary, type, serializer, throwOnError, out convertedObject);
     }
     IList list = o as IList;
     if (list != null)
     {
         IList list2;
         if (ConvertListToObject(list, type, serializer, throwOnError, out list2))
         {
             convertedObject = list2;
             return true;
         }
         convertedObject = null;
         return false;
     }
     if ((type == null) || (o.GetType() == type))
     {
         convertedObject = o;
         return true;
     }
     //TypeDescriptor.GetConverter(type) !!!
     TypeConverter converter = new TypeConverter();
     if (converter.CanConvertFrom(o.GetType()))
     {
         try
         {
             convertedObject = converter.ConvertFrom(null, CultureInfo.InvariantCulture, o);
             return true;
         }
         catch
         {
             if (throwOnError)
             {
                 throw;
             }
             convertedObject = null;
             return false;
         }
     }
     if (converter.CanConvertFrom(typeof(string)))
     {
         try
         {
             string str;
             if (o is DateTime)
             {
                 DateTime time = (DateTime)o;
                 str = time.ToUniversalTime().ToString("u", CultureInfo.InvariantCulture);
             }
             else
             {
                 //ConvertToInvariantString(o); !!!
                 str = converter.ConvertToString(o);
             }
             //ConvertFromInvariantString(str); !!!
             convertedObject = converter.ConvertToString(str);
             return true;
         }
         catch
         {
             if (throwOnError)
             {
                 throw;
             }
             convertedObject = null;
             return false;
         }
     }
     if (type.IsAssignableFrom(o.GetType()))
     {
         convertedObject = o;
         return true;
     }
     if (throwOnError)
     {
         throw new InvalidOperationException(string.Format(CultureInfo.CurrentCulture, AtlasWeb.JSON_CannotConvertObjectToType, new object[] { o.GetType(), type }));
     }
     convertedObject = null;
     return false;
 }

		/// <summary>
		/// Creates a new instance of the ConfigurationProperty class.
		/// </summary>
		/// <param name="name">The name of the xml entity.</param>
		/// <param name="type">The type of the xml entity.</param>
		/// <param name="defaultValue">The default value of the xml entity.</param>
		/// <param name="converter">The type of the converter to apply.</param>
		/// <param name="validation">The validator to use.</param>
		/// <param name="flags">One of the APXmlPropertyOptions enumeration values.</param>
		/// <param name="description">The description of the xml entity.</param>
		public APXmlProperty(string name, Type type, object defaultValue,
			TypeConverter converter, APValidatorBase validation, APXmlPropertyOptions flags, string description)
		{
			_name = name;

			_converter = converter != null ? converter : TypeDescriptor.GetConverter(type);

			if (defaultValue != null)
			{
				if (defaultValue == NoDefaultValue)
				{
					switch (Type.GetTypeCode(type))
					{
						case TypeCode.Object:
							defaultValue = null;
							break;
						case TypeCode.String:
							defaultValue = String.Empty;
							break;
						default:
							defaultValue = Activator.CreateInstance(type);
							break;
					}
				}
				else
				{
					if (!type.IsAssignableFrom(defaultValue.GetType()))
					{
						if (!_converter.CanConvertFrom(defaultValue.GetType()))
							throw new APXmlException(APResource.GetString(APResource.APXml_DefaultValueTypeError, name, type, defaultValue.GetType()));
						defaultValue = _converter.ConvertFrom(defaultValue);
					}
				}
			}

			_defaultValue = defaultValue;
			_flags = flags;
			_type = type;
			_validation = validation != null ? validation : new DefaultAPValidator();
			_description = description;
		}

		public virtual object ParseFormattedValue (object formattedValue, DataGridViewCellStyle cellStyle, TypeConverter formattedValueTypeConverter, TypeConverter valueTypeConverter)
		{
			if (cellStyle == null)
				throw new ArgumentNullException ("cellStyle is null.");
			if (FormattedValueType == null)
				throw new FormatException ("The System.Windows.Forms.DataGridViewCell.FormattedValueType property value is null.");
			if (formattedValue == null)
				throw new ArgumentException ("formattedValue is null.");
			if (ValueType == null)
				throw new FormatException ("valuetype is null");
			if (!FormattedValueType.IsAssignableFrom (formattedValue.GetType ()))
				throw new ArgumentException ("formattedValue is not of formattedValueType.");
			
			if (formattedValueTypeConverter == null)
				formattedValueTypeConverter = FormattedValueTypeConverter;
			if (valueTypeConverter == null)
				valueTypeConverter = ValueTypeConverter;

			if (valueTypeConverter != null && valueTypeConverter.CanConvertFrom (FormattedValueType))
				return valueTypeConverter.ConvertFrom (formattedValue);
			if (formattedValueTypeConverter != null && formattedValueTypeConverter.CanConvertTo (ValueType))
				return formattedValueTypeConverter.ConvertTo (formattedValue, ValueType);
			return Convert.ChangeType (formattedValue, ValueType);
		}