handconverter.cs

中文名：Windows Forms 程序设计 英文名：Windows Forms Programming in c# 作者： Chris Sells 翻译： 荣耀 蒋贤哲 出版社：人民

#region Using directives

using System;
using System.Collections;
using System.Collections.Generic;
using System.ComponentModel;
using System.ComponentModel.Design.Serialization;
using System.Drawing;
using System.Globalization;
using System.Reflection;
using System.Text;

#endregion

namespace AlarmClockControlLibrary {
  public class HandConverter : ExpandableObjectConverter {
    // Don't need to override CanConvertTo if converting to string, as that's what base TypeConverter does
    // Do need to override CanConvertFrom since it's base converts from InstanceDescriptor

    public override bool CanConvertTo(ITypeDescriptorContext context, Type destinationType) {
      // We can be converted to a string or an InstanceDescriptor
      if( destinationType == typeof(string) ) return true;
      if( destinationType == typeof(InstanceDescriptor) ) return true;
      return base.CanConvertTo(context, destinationType);
    }

    public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType) {
      // We can convert from a string to a Hand type
      if( sourceType == typeof(string) ) { return true; }
      return base.CanConvertFrom(context, sourceType);
    }

    public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo info, object value) {

      // If converting from a string
      if( value is string ) {
        // Build a Hand type
        try {
          // Get Hand properties
          string propertyList = (string)value;
          string[] properties = propertyList.Split(';');
          return new Hand(Color.FromName(properties[0].Trim()),
                          Convert.ToInt32(properties[1]));
        }
        catch { }
        throw new ArgumentException("The arguments were not valid.");
      }
      return base.ConvertFrom(context, info, value);
    }

    public override object ConvertTo(ITypeDescriptorContext context, CultureInfo culture, object value, Type destinationType) {

      // If source value is a Hand type
      if( value is Hand ) {
        // Convert to string
        if( (destinationType == typeof(string)) ) {
          Hand hand = (Hand)value;
          string color;
          if( hand.Color.IsNamedColor ) {
            color = hand.Color.Name;
          }
          else {
            color = string.Format("{0}, {1}, {2}", hand.Color.R, hand.Color.G, hand.Color.B);
          }
          return string.Format("{0}; {1}", color, hand.Width.ToString());
        }
        // Convert to InstanceDescriptor
        if( (destinationType == typeof(InstanceDescriptor)) ) {
          Hand hand = (Hand)value;
          object[] properties = new object[2];
          Type[] types = new Type[2];

          // Color
          types[0] = typeof(Color);
          properties[0] = hand.Color;

          // Width
          types[1] = typeof(int);
          properties[1] = hand.Width;

          // Build constructor
          ConstructorInfo ci = typeof(Hand).GetConstructor(types);
          return new InstanceDescriptor(ci, properties);
        }
      }
      // Base ConvertTo if neither string or InstanceDescriptor required
      return base.ConvertTo(context, culture, value, destinationType);
    }


    public override bool GetCreateInstanceSupported(ITypeDescriptorContext context) {

      // Always force a new instance
      return true;
    }

    public override object CreateInstance(ITypeDescriptorContext context, IDictionary propertyValues) {

      // Use the dictionary to create a new instance
      return new Hand((Color)propertyValues["Color"], (int)propertyValues["Width"]);
    }
  }
}