Writing Reusable JsonConverters for json.net
I am requesting a service that returns a list of tags in several formats:
{
"tags": "a,b,c"
}
or
{
"tags": "a b c"
}
or
{
"tags": "a+b+c"
}
The object I want to deserialize this for is List<string>
. I wrote a TagsConverter
that implements the required methods in the JsonConverter
following way:
public class TagsConverter : JsonConverter
{
public override bool CanConvert(Type objectType)
{
return (objectType == typeof(string));
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
return reader
.Value
.ToString()
.Split(' ')
.ToList();
}
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
var list = (List<string>)value;
var delimitedList = string.Join(" ", list);
writer.WriteValue(delimitedList);
}
}
Then I annotate the field in the object like so:
public class Foo
{
[JsonConverter(typeof(TagsConverter))]
public List<string> Tags { get; set; }
}
And it works, but only for tags separated by spaces.
However, it TagsConverter
can work in all three scenarios if I can just change the functions Split
and in a Join
parameterized manner. But since we are only passing the type to the attribute JsonConverter
, I understand that we cannot pass the "separator" as an argument.
Is there a way to achieve this?
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There is an additional JsonConverter
constructor overload that takes both a type and a params object[] converterParameters
, which is injected into a specific instance of your converter. You can take advantage of this overload to maximize reuse.
public class TagsConverter : JsonConverter
{
private readonly string _delimiter;
public TagsConverter(string delimiter)
{
_delimiter = delimiter;
}
public override bool CanConvert(Type objectType)
{
return (objectType == typeof(string));
}
public override object ReadJson(JsonReader reader, Type objectType,
object existingValue, JsonSerializer serializer)
{
return reader
.Value
.ToString()
.Split(_delimiter.ToCharArray())
.ToList();
}
public override void WriteJson(JsonWriter writer, object value,
JsonSerializer serializer)
{
var list = (List<string>)value;
var delimitedList = string.Join(_delimiter, list);
writer.WriteValue(delimitedList);
}
}
Using an overload is as simple as passing it as a second parameter:
public class Foo
{
[JsonConverter(typeof(TagsConverter), " ")]
public List<string> Tags { get; set; }
}
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If only read / deserialize JSON is required, please note that it string.Split
can accept a character arraychar[]
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
return reader
.Value
.ToString()
.Split(new char[]{' ', ',', '+'}, StringSplitOptions.RemoveEmptyEntries)
.ToList();
}
This means that the converter can handle all three delimiters when reading.
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