/// <summary>
/// 将给定的对象转换为给定类型的枚举值。
/// </summary>
/// <param name="enumType">枚举对象类型。</param>
/// <param name="existingValue">已有的对象。</param>
/// <returns></returns>
/// <exception cref="ArgumentNullException">
/// <paramref name="enumType"/> 为 null
/// 或
/// <paramref name="existingValue"/> 为 null。
/// </exception>
/// <exception cref="InvalidOperationException">
/// <paramref name="existingValue"/> 是一个字符串序列但是枚举类型不是 flags 枚举
/// 或
/// 无法将 <paramref name="existingValue"/> 的类型转换到给定的枚举类型。
/// </exception>
private static object GetEnumFromExistingValue(Type enumType, object existingValue)
{
Contract.NotNull(enumType, nameof(enumType));
Contract.NotNull(existingValue, nameof(existingValue));
var enumInfo = EnumInfo.From(enumType);
var existingType = existingValue.GetType();
if (existingType.IsEnum)
{
return(GetEnumFromExistingEnum(enumType, (Enum)existingValue));
}
if (existingType == typeof(string))
{
return(GetEnumFromExistingString(enumType, (string)existingValue));
}
if (existingType.IsPrimitive &&
existingType != typeof(bool) &&
existingType != typeof(float) &&
existingType != typeof(double))
{
return(GetEnumFromExistingInteger(enumType, existingValue, enumInfo));
}
if (existingType.GetInterfaces().Contains(typeof(IEnumerable <string>)))
{
return(GetEnumFromExistingStrings(enumType, (IEnumerable <string>)existingValue, enumInfo));
}
if (existingValue.GetType().IsSubclassOf(typeof(JToken)))
{
return(GetEnumFromExistingJToken(enumType, (JToken)existingValue, enumInfo));
}
throw new InvalidOperationException(
$"Enum of type {enumType} cannot be constructed from object of type {existingType}.");
}
/// <inheritdoc />
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
var enumValue = (Enum)value;
var enumInfo = EnumInfo.From(enumValue.GetType());
if (!enumInfo.HasFlags(enumValue))
{
// enumValue 无法用枚举值进行异或表出。此时应使用 enumValue 的数值进行序列化。
if (enumInfo.IsSigned)
{
serializer.Serialize(writer, Convert.ToInt64(enumValue));
}
else
{
serializer.Serialize(writer, Convert.ToUInt64(enumValue));
}
return;
}
if (!enumInfo.IsFlags)
{
serializer.Serialize(writer, enumValue.ToString());
return;
}
var components = enumInfo.GetComponents(enumValue);
if (components.Length == 1)
{
serializer.Serialize(writer, components[0].ToString());
}
else
{
serializer.Serialize(writer, components.Select(e => e.ToString()));
}
}