从您的问题和评论,这听起来像你有一些情况下,你希望一个转换器读取,但不写,其他人希望它写但没有阅读。通过将功能分成两个转换器,然后让每个转换器的CanConvert
方法在适当的时候返回true或false,你已经解决了这个问题。这当然是一种可行的方法,并且似乎为你工作,这非常棒。不过,我想提供一个替代解决方案。
除了CanConvert
方法,基地JsonConverter
提供了两个可以覆盖的虚拟布尔属性:CanRead
和CanWrite
。 (默认情况下均返回true。)这些属性直接控制序列化程序是否为特定转换器调用ReadJson
和WriteJson
。因此,例如,如果CanRead
返回false,则不会调用ReadJson
,但将使用默认读取行为,即使CanConvert
返回true。这使您可以非常整洁地设置不对称转换器。例如,您可能会遇到这种情况,您想要将一种疯狂的JSON格式反序列化为更加健全的对象结构,但是当您再次序列化它时,您不想回到疯狂的JSON格式 - 您只需要默认序列化。在这种情况下,您将在转换器中覆盖CanWrite
以始终返回false。然后,你可以将WriteJson
的执行留空或让它出现NotImplementedException
;它永远不会被调用。
你的情况听起来有点复杂,但你仍然应该能够操纵CanRead
和CanWrite
属性来实现你想要的结果。以下是一个人为的例子,它展示了我们如何根据情境变量打开和关闭ReadJson
和WriteJson
方法。
public class Program
{
public static void Main(string[] args)
{
string json = @"{""keys"":[""foo"",""fizz""],""values"":[""bar"",""bang""]}";
CustomConverter converter = new CustomConverter();
JsonSerializerSettings settings = new JsonSerializerSettings();
settings.Converters.Add(converter);
// Here we are reading a JSON object containing two arrays into a dictionary
// (custom read) and then writing out the dictionary JSON (standard write)
Console.WriteLine("--- Situation 1 (custom read, standard write) ---");
converter.Behavior = ConverterBehavior.CustomReadStandardWrite;
json = DeserializeThenSerialize(json, settings);
// Here we are reading a simple JSON object into a dictionary (standard read)
// and then writing out a new JSON object containing arrays (custom write)
Console.WriteLine("--- Situation 2 (standard read, custom write) ---");
converter.Behavior = ConverterBehavior.StandardReadCustomWrite;
json = DeserializeThenSerialize(json, settings);
}
private static string DeserializeThenSerialize(string json, JsonSerializerSettings settings)
{
Console.WriteLine("Deserializing...");
Console.WriteLine(json);
var dict = JsonConvert.DeserializeObject<Dictionary<string, string>>(json, settings);
foreach (var kvp in dict)
{
Console.WriteLine(kvp.Key + ": " + kvp.Value);
}
Console.WriteLine("Serializing...");
json = JsonConvert.SerializeObject(dict, settings);
Console.WriteLine(json);
Console.WriteLine();
return json;
}
}
enum ConverterBehavior { CustomReadStandardWrite, StandardReadCustomWrite }
class CustomConverter : JsonConverter
{
public ConverterBehavior Behavior { get; set; }
public override bool CanConvert(Type objectType)
{
return typeof(IDictionary<string, string>).IsAssignableFrom(objectType);
}
public override bool CanRead
{
get { return Behavior == ConverterBehavior.CustomReadStandardWrite; }
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
Console.WriteLine("ReadJson was called");
// Converts a JSON object containing a keys array and a values array
// into a Dictionary<string, string>
JObject jo = JObject.Load(reader);
return jo["keys"].Zip(jo["values"], (k, v) => new JProperty((string)k, v))
.ToDictionary(jp => jp.Name, jp => (string)jp.Value);
}
public override bool CanWrite
{
get { return Behavior == ConverterBehavior.StandardReadCustomWrite; }
}
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
Console.WriteLine("WriteJson was called");
// Converts a dictionary to a JSON object containing
// a keys array and a values array from the dictionary
var dict = (Dictionary<string, string>)value;
JObject jo = new JObject(new JProperty("keys", new JArray(dict.Keys)),
new JProperty("values", new JArray(dict.Values)));
jo.WriteTo(writer);
}
}
输出:
--- Situation 1 (custom read, standard write) ---
Deserializing...
{"keys":["foo","fizz"],"values":["bar","bang"]}
ReadJson was called
foo: bar
fizz: bang
Serializing...
{"foo":"bar","fizz":"bang"}
--- Situation 2 (standard read, custom write) ---
Deserializing...
{"foo":"bar","fizz":"bang"}
foo: bar
fizz: bang
Serializing...
WriteJson was called
{"keys":["foo","fizz"],"values":["bar","bang"]}
小提琴:https://dotnetfiddle.net/BdtSoN
*事实上,在一些情况下,我可以而且应该创建对象*什么情景?当ReadJson应该处理这个对象的时候,什么时候应该处理这个对象呢? –
我现在意识到我可以将读取(反序列化)和写入(序列化)分离为单独的转换器类,从而解决了我的问题。我原本以为CanConvert必须处理这两种情况。 CanConvert需要在写入端返回true,而在读取端则返回false。因此,我只是返回true(以便写入工作),并且我试图调用ReadJson来忽略它被调用的事实。 – SFun28