/// <summary>
/// 返回的将对象从 <paramref name="inputType"/> 类型转换为 <paramref name="outputType"/>
/// 类型的用户自定义类型转换。
/// </summary>
/// <param name="inputType">要转换的对象的类型。</param>
/// <param name="outputType">要将输入对象转换到的类型。</param>
/// <returns>将对象从 <paramref name="inputType"/> 类型转换为 <paramref name="outputType"/>
/// 类型的用户自定义类型转换，如果不存在则为 <c>null</c>。</returns>
private static Conversion GetUserDefinedConversion(Type inputType, Type outputType)
{
Contract.Requires(inputType != null && outputType != null &&
inputType != typeof(void) && outputType != typeof(void));
// 判断可空类型。
Type inputUnderlyingType = inputType.GetNonNullableType();
Type outputUnderlyingType = outputType.GetNonNullableType();
MethodInfo method = UserConversionCache.GetConversion(inputUnderlyingType, outputUnderlyingType);
if (method == null)
{
return(null);
}
Conversion conversion = new UserConversion(method);
// 存入缓存。
Type methodInputType = method.GetParametersNoCopy()[0].ParameterType;
Tuple <Type, Type> key = new Tuple <Type, Type>(inputType, outputType);
if (inputType != methodInputType || outputType != method.ReturnType)
{
conversion = userDefinedConverers.GetOrAdd(new Tuple <Type, Type>(methodInputType, method.ReturnType),
conversion);
}
if (inputUnderlyingType != inputType || outputUnderlyingType != outputType)
{
userDefinedConverers.TryAdd(new Tuple <Type, Type>(inputUnderlyingType, outputUnderlyingType), conversion);
}
if (inputUnderlyingType == inputType || !methodInputType.IsValueType || methodInputType.IsNullable())
{
return(userDefinedConverers.GetOrAdd(key, conversion));
}
// 需要将输入的 Nullable<T> 解包。
if (outputUnderlyingType != outputType || !outputType.IsValueType)
{
// outputType 可以为 null（引用类型或 Nullable<T>）。
return(userDefinedConverers.GetOrAdd(key, BetweenNullableConversion.UserDefined));
}
return(userDefinedConverers.GetOrAdd(key, FromNullableConversion.UserDefined));
}
/// <summary>
/// 写入类型转换的 IL 指令。
/// </summary>
/// <param name="generator">IL 的指令生成器。</param>
/// <param name="inputType">要转换的对象的类型。</param>
/// <param name="outputType">要将输入对象转换到的类型。</param>
/// <param name="isChecked">是否执行溢出检查。</param>
public override void Emit(ILGenerator generator, Type inputType, Type outputType, bool isChecked)
{
Contract.Assume((inputType == typeof(decimal) && outputType.IsNumeric()) ||
(outputType == typeof(decimal) && inputType.IsNumeric()));
MethodInfo method;
if (inputType == typeof(decimal))
{
if (outputType.IsEnum)
{
outputType = Enum.GetUnderlyingType(outputType);
}
method = UserConversionCache.GetConversionTo(inputType, outputType);
}
else
{
if (inputType.IsEnum)
{
inputType = Enum.GetUnderlyingType(inputType);
}
method = UserConversionCache.GetConversionFrom(outputType, inputType);
}
generator.EmitCall(method);
}