NullableConverter.cs :  » 2.6.4-mono-.net-core » System.ComponentModel » System » ComponentModel » C# / CSharp Open Source

//
// NullableConverter.cs
//
// Author:
//  Atsushi Enomoto  <atsushi@ximian.com>
//      Ivan N. Zlatev  <contact@i-nz.net>
//
// Copyright (C) 2007 Novell, Inc. http://www.novell.com
//

//
// Permission is hereby granted, free of charge, to any person obtaining
// a copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
// without limitation the rights to use, copy, modify, merge, publish,
// distribute, sublicense, and/or sell copies of the Software, and to
// permit persons to whom the Software is furnished to do so, subject to
// the following conditions:
// 
// The above copyright notice and this permission notice shall be
// included in all copies or substantial portions of the Software.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
// LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
// WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//

#if NET_2_0

using System;
using System.Collections;
using System.Globalization;

namespace System.ComponentModel{
  public class NullableConverter : TypeConverter
  {
    private Type nullableType;
    private Type underlyingType;
    private TypeConverter underlyingTypeConverter;

    public NullableConverter (Type nullableType)
    {
      if (nullableType == null)
        throw new ArgumentNullException ("nullableType");

      this.nullableType = nullableType;
      underlyingType = Nullable.GetUnderlyingType (nullableType);
      underlyingTypeConverter = TypeDescriptor.GetConverter (underlyingType);
    }

    public override bool CanConvertFrom (ITypeDescriptorContext context, Type sourceType)
    {
      if (sourceType == underlyingType)
        return true;

      if (underlyingTypeConverter != null)
        return underlyingTypeConverter.CanConvertFrom (context, sourceType);

      return base.CanConvertFrom (context, sourceType);
    }

    public override bool CanConvertTo (ITypeDescriptorContext context, Type destinationType)
    {
      if (destinationType == underlyingType)
        return true;

      if (underlyingTypeConverter != null)
        return underlyingTypeConverter.CanConvertTo (context, destinationType);

      return base.CanConvertFrom (context, destinationType);
    }

    public override object ConvertFrom (ITypeDescriptorContext context, CultureInfo culture, object value)
    {
      // Because:
      //    1) Nullable<> has an expliciit generic cast operator
      //    2) We are returning an "Object" type here
      // we don't have to bother creating the nullable instance,
      // since the user will have to explicitly cast anyway.
      //
      if (value == null || value.GetType() == underlyingType)
        return value;

      if (value is string && String.IsNullOrEmpty ((string)value))
        return null;

      if (underlyingTypeConverter != null)
        return underlyingTypeConverter.ConvertFrom (context, culture, value);

      return base.ConvertFrom (context, culture, value);
    }

    public override object ConvertTo (ITypeDescriptorContext context, CultureInfo culture, object value, Type destinationType)
    {
      if (destinationType == null)
        throw new ArgumentNullException ("destinationType");

      // Explicit cast operator in Nullable when the user casts will take care 
      // of extracting the inner value.
      if (destinationType == underlyingType && value.GetType() == nullableType)
        return value;

      if (underlyingTypeConverter != null && value != null)
        return underlyingTypeConverter.ConvertTo (context, culture, value, destinationType);

      return base.ConvertTo (context, culture, value, destinationType);
    }

    public override object CreateInstance (ITypeDescriptorContext context, IDictionary propertyValues)
    {
      if (underlyingTypeConverter != null)
        return underlyingTypeConverter.CreateInstance (context, propertyValues);

      return base.CreateInstance (context, propertyValues);
    }

    public override bool GetCreateInstanceSupported (ITypeDescriptorContext context)
    {
      if (underlyingTypeConverter != null)
        return underlyingTypeConverter.GetCreateInstanceSupported (context);

      return base.GetCreateInstanceSupported (context);
    }

    public override PropertyDescriptorCollection GetProperties (ITypeDescriptorContext context, object value, Attribute [] attributes)
    {
      if (underlyingTypeConverter != null)
        return underlyingTypeConverter.GetProperties (context, value, attributes);

      return base.GetProperties (context, value, attributes);
    }

    public override bool GetPropertiesSupported (ITypeDescriptorContext context)
    {
      if (underlyingTypeConverter != null)
        return underlyingTypeConverter.GetCreateInstanceSupported (context);

      return base.GetCreateInstanceSupported (context);
    }

    public override TypeConverter.StandardValuesCollection GetStandardValues (ITypeDescriptorContext context)
    {
      // Adds a "null" values to the standard values if supported and available
      //
      if (underlyingTypeConverter != null && 
          underlyingTypeConverter.GetStandardValuesSupported (context)) {
        TypeConverter.StandardValuesCollection values = underlyingTypeConverter.GetStandardValues (context);
        if (values != null) {
          ArrayList valuesWithNull = new ArrayList (values);
          valuesWithNull.Add (null);
          return new TypeConverter.StandardValuesCollection (valuesWithNull);
        }
      }

      return base.GetStandardValues (context);
    }

    public override bool GetStandardValuesExclusive (ITypeDescriptorContext context)
    {

      if (underlyingTypeConverter != null)
        return underlyingTypeConverter.GetStandardValuesExclusive (context);

      return base.GetStandardValuesExclusive (context);
    }

    public override bool GetStandardValuesSupported (ITypeDescriptorContext context)
    {
      if (underlyingTypeConverter != null)
        return underlyingTypeConverter.GetStandardValuesSupported (context);

      return base.GetStandardValuesSupported (context);
    }

    public override bool IsValid (ITypeDescriptorContext context, object value)
    {
      if (underlyingTypeConverter != null)
        return underlyingTypeConverter.IsValid (context, value);

      return base.IsValid (context, value);
    }

    public Type NullableType {
      get { return nullableType; }
    }

    public Type UnderlyingType {
      get { return underlyingType; }
    }

    public TypeConverter UnderlyingTypeConverter {
      get { return underlyingTypeConverter; }
    }
  }
}

#endif