C# TypeConverter.ConvertTo方法代碼示例

 private DateTime GetDateTime(object value, TypeConverter converter)
 {
     if (typeof(DateTime).IsAssignableFrom(value.GetType()))
         return (DateTime) value;
     else
         return (DateTime) converter.ConvertTo(value, typeof(DateTime));
 }

		protected virtual object GetFormattedValue (object value, int rowIndex, ref DataGridViewCellStyle cellStyle, TypeConverter valueTypeConverter, TypeConverter formattedValueTypeConverter, DataGridViewDataErrorContexts context)
		{
			if (DataGridView == null)
				return null;
				
			if (rowIndex < 0 || rowIndex >= DataGridView.RowCount)
				throw new ArgumentOutOfRangeException ("rowIndex");

			// Give the user a chance to custom format
			if (!(this is DataGridViewRowHeaderCell)) {
				DataGridViewCellFormattingEventArgs e = new DataGridViewCellFormattingEventArgs (ColumnIndex, rowIndex, value, FormattedValueType, cellStyle);
				DataGridView.OnCellFormattingInternal (e);
			
				if (e.FormattingApplied)
					return e.Value;
			
				cellStyle = e.CellStyle;
				value = e.Value;
			}
			
			if (value == null || (cellStyle != null && value == cellStyle.DataSourceNullValue)) {
				if (FormattedValueType == typeof (string))
					return String.Empty;
			}

			if (FormattedValueType == typeof(string) && value is IFormattable && !String.IsNullOrEmpty (cellStyle.Format))
				return ((IFormattable) value).ToString (cellStyle.Format, cellStyle.FormatProvider);
			if (value != null && FormattedValueType.IsAssignableFrom (value.GetType()))
				return value;

			if (formattedValueTypeConverter == null)
				formattedValueTypeConverter = FormattedValueTypeConverter;
			if (valueTypeConverter == null)
				valueTypeConverter = ValueTypeConverter;

			if (valueTypeConverter != null && valueTypeConverter.CanConvertTo (FormattedValueType))
				return valueTypeConverter.ConvertTo (value, FormattedValueType);
			if (formattedValueTypeConverter != null && formattedValueTypeConverter.CanConvertFrom (ValueType))
				return formattedValueTypeConverter.ConvertFrom (value);

			return Convert.ChangeType (value, FormattedValueType);
		}

        /// <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.........

		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);
		}

        /// <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));
        }

 private static object FormatObjectInternal(object value, System.Type targetType, TypeConverter sourceConverter, TypeConverter targetConverter, string formatString, IFormatProvider formatInfo, object formattedNullValue)
 {
     if ((value == DBNull.Value) || (value == null))
     {
         if (formattedNullValue != null)
         {
             return formattedNullValue;
         }
         if (targetType == stringType)
         {
             return string.Empty;
         }
         if (targetType == checkStateType)
         {
             return CheckState.Indeterminate;
         }
         return null;
     }
     if (((targetType == stringType) && (value is IFormattable)) && !string.IsNullOrEmpty(formatString))
     {
         return (value as IFormattable).ToString(formatString, formatInfo);
     }
     System.Type type = value.GetType();
     TypeConverter converter = TypeDescriptor.GetConverter(type);
     if (((sourceConverter != null) && (sourceConverter != converter)) && sourceConverter.CanConvertTo(targetType))
     {
         return sourceConverter.ConvertTo(null, GetFormatterCulture(formatInfo), value, targetType);
     }
     TypeConverter converter2 = TypeDescriptor.GetConverter(targetType);
     if (((targetConverter != null) && (targetConverter != converter2)) && targetConverter.CanConvertFrom(type))
     {
         return targetConverter.ConvertFrom(null, GetFormatterCulture(formatInfo), value);
     }
     if (targetType == checkStateType)
     {
         if (type == booleanType)
         {
             return (((bool) value) ? CheckState.Checked : CheckState.Unchecked);
         }
         if (sourceConverter == null)
         {
             sourceConverter = converter;
         }
         if ((sourceConverter != null) && sourceConverter.CanConvertTo(booleanType))
         {
             return (((bool) sourceConverter.ConvertTo(null, GetFormatterCulture(formatInfo), value, booleanType)) ? CheckState.Checked : CheckState.Unchecked);
         }
     }
     if (targetType.IsAssignableFrom(type))
     {
         return value;
     }
     if (sourceConverter == null)
     {
         sourceConverter = converter;
     }
     if (targetConverter == null)
     {
         targetConverter = converter2;
     }
     if ((sourceConverter != null) && sourceConverter.CanConvertTo(targetType))
     {
         return sourceConverter.ConvertTo(null, GetFormatterCulture(formatInfo), value, targetType);
     }
     if ((targetConverter != null) && targetConverter.CanConvertFrom(type))
     {
         return targetConverter.ConvertFrom(null, GetFormatterCulture(formatInfo), value);
     }
     if (!(value is IConvertible))
     {
         throw new FormatException(GetCantConvertMessage(value, targetType));
     }
     return ChangeType(value, targetType, formatInfo);
 }

 private static object ParseObjectInternal(object value, System.Type targetType, System.Type sourceType, TypeConverter targetConverter, TypeConverter sourceConverter, IFormatProvider formatInfo, object formattedNullValue)
 {
     if (EqualsFormattedNullValue(value, formattedNullValue, formatInfo) || (value == DBNull.Value))
     {
         return DBNull.Value;
     }
     TypeConverter converter = TypeDescriptor.GetConverter(targetType);
     if (((targetConverter != null) && (converter != targetConverter)) && targetConverter.CanConvertFrom(sourceType))
     {
         return targetConverter.ConvertFrom(null, GetFormatterCulture(formatInfo), value);
     }
     TypeConverter converter2 = TypeDescriptor.GetConverter(sourceType);
     if (((sourceConverter != null) && (converter2 != sourceConverter)) && sourceConverter.CanConvertTo(targetType))
     {
         return sourceConverter.ConvertTo(null, GetFormatterCulture(formatInfo), value, targetType);
     }
     if (value is string)
     {
         object obj2 = InvokeStringParseMethod(value, targetType, formatInfo);
         if (obj2 != parseMethodNotFound)
         {
             return obj2;
         }
     }
     else if (value is CheckState)
     {
         CheckState state = (CheckState) value;
         if (state == CheckState.Indeterminate)
         {
             return DBNull.Value;
         }
         if (targetType == booleanType)
         {
             return (state == CheckState.Checked);
         }
         if (targetConverter == null)
         {
             targetConverter = converter;
         }
         if ((targetConverter != null) && targetConverter.CanConvertFrom(booleanType))
         {
             return targetConverter.ConvertFrom(null, GetFormatterCulture(formatInfo), state == CheckState.Checked);
         }
     }
     else if ((value != null) && targetType.IsAssignableFrom(value.GetType()))
     {
         return value;
     }
     if (targetConverter == null)
     {
         targetConverter = converter;
     }
     if (sourceConverter == null)
     {
         sourceConverter = converter2;
     }
     if ((targetConverter != null) && targetConverter.CanConvertFrom(sourceType))
     {
         return targetConverter.ConvertFrom(null, GetFormatterCulture(formatInfo), value);
     }
     if ((sourceConverter != null) && sourceConverter.CanConvertTo(targetType))
     {
         return sourceConverter.ConvertTo(null, GetFormatterCulture(formatInfo), value, targetType);
     }
     if (!(value is IConvertible))
     {
         throw new FormatException(GetCantConvertMessage(value, targetType));
     }
     return ChangeType(value, targetType, formatInfo);
 }

		public void CheckConversion(object check, object expect, TypeConverter conv, Type type, bool test_from, bool test_to, CultureInfo culture) {
			object obj;
			object result;

			obj = check;

			if (debug > 0) {
				Console.WriteLine("{0}: CheckConversion, checking {1}({2}) <-> {3}({4})", conv.ToString(), check.GetType().ToString(), check.ToString(), type.ToString(), expect != null ? expect.ToString() : "null");
			}

			if (test_to) {
				obj = conv.ConvertTo(null, culture, check, type);

				if (obj == null) {
					if (expect != null) {
						failed++;
						Console.WriteLine("{0}: ConvertTo failed, type {1}, expected {2}, got null", conv.ToString(), type.ToString(), expect.ToString());
					}
					return;
				}

				// Intermediate verification
				if (expect != null && !obj.Equals(expect)) {
					failed++;
					if (verbose > 0) {
						Console.WriteLine("{0}: ConvertTo failed, type {1}, expected {2}, got {3}", conv.ToString(), type.ToString(), expect.ToString(), obj.ToString());
					}
				}

				if (debug > 1) {
					Console.WriteLine("{0}: CheckConversion, ConvertTo result: '{1}')", conv.ToString(), obj);
				}
			}


			if (test_from) {
				result = conv.ConvertFrom(null, culture, obj);

				if (test_to) {
					// Roundtrip check
					if (!check.Equals(result)) {
						failed++;
						if (verbose > 0) {
							Console.WriteLine("{0}: ConvertTo/ConvertFrom roundtrip failed, type {1}", conv.ToString(), type.ToString());
						}
					}

				} else {
					if (!expect.Equals(result)) {
						failed++;
						if (verbose > 0) {
							Console.WriteLine("{0}: ConvertFrom failed, type {1}", conv.ToString(), type.ToString());
						}
					}
				}

				if (debug > 1) {
					Console.WriteLine("{0}: CheckConversion, ConvertFrom result: '{1}')", conv.ToString(), result);
				}
			}
		}

      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;
      }