检索自定义属性中的属性值

Question

Right now I have an attribute called Checkbox. We're using it because of our front end posts "On" and "Off" instead of true/false when a checkbox value is submitted.

Our goal is to parse the on/off values and convert them to true/false before they get to the JSON converter, so they can be picked up as a boolean.

I've considered using this attribute to handle that.

    [Checkbox]
    [JsonConverter(typeof(InvariantConverter))]
    public bool CheckboxInputValue { get; set; }

I need access to the value of the property inside of the checkbox attribute and then need the ability to modify the value.

Open to suggestions and thoughts here.

Answer 1

You cannot store per-instance data in an attribute property since the attribute is created when using the reflection API on the class.

You should rather use a custom JSON converter to convert between the string values and the boolean value.

Answer 2

As Martin Ullrich already suggested you should consider using a dedicated JSON converter.

I left null value handling for you.

public class OnOffStringToBoolConverter : JsonConverter
{
    private readonly Type _sourceType = typeof(string);
    private readonly Type _targetType = typeof(bool);

    public OnOffStringToBoolConverter()
    {

    }

    public override bool CanRead => true;

    public override bool CanWrite => true;

    public override bool CanConvert(Type objectType)
    {
        if (objectType == null)
        {
            throw new ArgumentNullException(nameof(objectType));
        }

        return objectType == _sourceType;
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        if (reader == null)
        {
            throw new ArgumentNullException(nameof(reader));
        }

        if (objectType == null)
        {
            throw new ArgumentNullException(nameof(objectType));
        }

        if (serializer == null)
        {
            throw new ArgumentNullException(nameof(serializer));
        }

        if (reader.Value == null)
        {
            // Add some null handling logic here if needed.
            throw new JsonSerializationException(
                $"Unable to deserialize null value to {_targetType.Name}.");
        }

        if (string.Compare(reader.Value.ToString(), "On", StringComparison.OrdinalIgnoreCase) == 0)
        {
            return true;
        }

        if (string.Compare(reader.Value.ToString(), "Off", StringComparison.OrdinalIgnoreCase) == 0)
        {
            return false;
        }

        throw new JsonSerializationException(
            $"Unable to deserialize '{reader.Value}' to {_targetType.FullName}. " +
            $"This converter supports only \"On\", \"Off\" values.");

    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        if (writer == null)
        {
            throw new ArgumentNullException(nameof(writer));
        }

        if (serializer == null)
        {
            throw new ArgumentNullException(nameof(serializer));
        }

        if (value == null)
        {
            // Add some null handling logic here if needed.
            throw new JsonSerializationException("Unable to serialize null value.");
        }

        // Write value only if it is boolean type.
        if (value is bool boolValue)
        {
            writer.WriteValue(boolValue ? "On" : "Off");
        }
        else
        {
            throw new JsonSerializationException(
                $"Unable to serialize '{value}' of type {value.GetType().FullName}. " +
                $"This converter supports deserialization of values " +
                $"of {_targetType.FullName} type only.");
        }
    }
}