I have an object with a number of public properties where one is of type image. I am trying to serialise this using json.net and assume that I will need to base64 encode this and serialise the resultant string. I have tried with the BinaryConverter against the property without success below
public class Person
{
public string name { get; set; }
public int age { get; set; }
[JsonConverter(typeof(BinaryConverter))]
public Image photo { get; set; }
public string ToJson()
{
return JsonConvert.SerializeObject(this);
}
}
When called with this test code...
var p = new Person();
p.name = "John Doe";
p.age = 99;
p.photo = Image.FromFile(@"dea4007a-c812-41e9-b09a-c7793c6e853d.jpg");
var json = p.ToJson();
Console.WriteLine(json);
Console.ReadKey();
I get an exception "Unexpected value type when writing binary". Any help would be very helpful as I have been searching the web for a while now without success.
Json.NET has no idea about what is Image
, so you have to help it a bit, for example by using a converter ( BinaryConverter
is not for images):
public class ImageConverter : JsonConverter
{
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer) {
var base64 = (string)reader.Value;
// convert base64 to byte array, put that into memory stream and feed to image
return Image.FromStream(new MemoryStream(Convert.FromBase64String(base64)));
}
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer) {
var image = (Image) value;
// save to memory stream in original format
var ms = new MemoryStream();
image.Save(ms, image.RawFormat);
byte[] imageBytes = ms.ToArray();
// write byte array, will be converted to base64 by JSON.NET
writer.WriteValue(imageBytes);
}
public override bool CanConvert(Type objectType) {
return objectType == typeof(Image);
}
}
public class Person
{
public string name { get; set; }
public int age { get; set; }
[JsonConverter(typeof(ImageConverter))]
public Image photo { get; set; }
public string ToJson()
{
return JsonConvert.SerializeObject(this);
}
}
Then it will both serialize and deserialize your class just fine.
在这种情况下,我建议将图像转换为base64,然后将其序列化,这里是一个如何在C#中执行此操作的示例: 将图像转换为Base64
Construct a JSONConverter class as follows:
public class ImageJsonConverter
: JsonConverter<Image>
{
public override void WriteJson(JsonWriter writer, Image value, JsonSerializer serializer)
{
if (value == null)
{
writer.WriteNull();
return;
}
// Save to memory stream in original format.
using (MemoryStream ms = new MemoryStream())
{
Image image = value;
image.Save(ms, image.RawFormat);
byte[] imageBytes = ms.ToArray();
// Write byte array, will be converted to base64 by JSON.NET.
writer.WriteValue(imageBytes);
}
}
public override Image ReadJson(JsonReader reader, Type objectType, Image existingValue, bool hasExistingValue, JsonSerializer serializer)
{
if (reader.TokenType == JsonToken.String)
{
string base64 = reader.Value?.ToString();
if (string.IsNullOrEmpty(base64))
{
return null;
}
// Convert base64 to byte array,
// put that into memory stream and feed to image.
return Image.FromStream(new MemoryStream(Convert.FromBase64String(base64)));
}
return null;
}
}
Then use the JsonConverterAttribute
to specify that a JsonConverter should be used when serializing and deserializing a property.
public class Person
{
public string name { get; set; }
public int age { get; set; }
[JsonConverter(typeof(ImageJsonConverter))]
public Image photo { get; set; }
public string ToJson()
{
return JsonConvert.SerializeObject(this);
}
}
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