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System.Text.Json – How to serialize cycling property of the object as a string

I have a problem with the default Serialization of my object.

public interface IUserProduct
{
    public int Gramature { get; set; }
    public ImageSource ProductImage { get; }
    public string Name { get; }
    public decimal Kcal { get; }
    public decimal Carbohydrates { get; }
    public decimal Fat { get; }
    public decimal Proteins { get; }
    public IProductDataTemplate ProductTemplate { get; set; }
}

The object has a property ImageSource, unfortunately it is referring to itself, and I’m getting a System.Text.Json.JsonException: 'A possible object cycle was detected. exception.

I have built a custom converter that is replacing a ImageSource with a string but Im still getting the exception.

public override void Write(Utf8JsonWriter writer, IList<IUserProduct> value, JsonSerializerOptions options)
{
    writer.WriteStartArray();
    foreach (IUserProduct product in value)
    {
        writer.WriteStartObject();
        writer.WriteString(nameof(product.Name), product.Name);
        writer.WriteNumber(nameof(product.Kcal), product.Kcal);
        writer.WriteNumber(nameof(product.Gramature), product.Gramature);
        writer.WriteNumber(nameof(product.Proteins), product.Proteins);
        writer.WriteNumber(nameof(product.Carbohydrates), product.Carbohydrates);
        writer.WriteNumber(nameof(product.Fat), product.Fat);
        string image = product.ProductImage.ToString();
        writer.WriteString(nameof(product.ProductImage), image);
        writer.WriteEndObject();
    }
    writer.WriteEndArray();
}

I have tried adding ReferenceHandler.Preserve and ReferenceHandler.IgnoreCycles but it doesn’t work neither.

This is a method that throws the exception:

private static readonly JsonSerializerOptions ProductSerializer = new JsonSerializerOptions() 
{
    Converters = { new JsonProductCustomConverter() }//this is my custom converter
};

private static void WriteProductsJSON(IUserProduct product, string fileName)
{
    string json;
    List<IUserProduct> products = new List<IUserProduct>();
    if (File.Exists(Path.Combine(DataPath, fileName)))
    {
        json = File.ReadAllText(Path.Combine(DataPath, fileName));
        products = System.Text.Json.JsonSerializer.Deserialize<List<IUserProduct>>(json, options: ProductSerializer);
    }
    products.Add(product);
    json = System.Text.Json.JsonSerializer.Serialize(products, options: ProductSerializer);
    File.WriteAllText(Path.Combine(DataPath, fileName), json);
}

What am I doing wrong? How can I serialize this ImageSource as a string and remove the exception?

Tags:

2

Answers


  1. Chosen as BEST ANSWER
    0

    The problem was lying in the JsonConverter I had made, I did not understand how it worked correctly. CustomJsonConverter that inherits from JsonConverter<T> is not passing the whole object meant for serialization to the public override void Write(Utf8JsonWriter writer, IList<IUserProduct> value, JsonSerializerOptions options) it only passes individual properties of that object to the method.

    In order to target a single property of type T to conversion, the type of that property should be specified in a custom-made converter. So, to custom serialize a ImageSource as a string the converter should look like this in my case:

    public override void Write(Utf8JsonWriter writer, ImageSource value, JsonSerializerOptions options)
{
    if (value as FileImageSource != null)
    {
        FileImageSource image = value as FileImageSource;
        writer.WriteStringValue(image.File.ToString());
    }
    else if (value as UriImageSource != null)
    {
        UriImageSource image = value as UriImageSource;
        writer.WriteStringValue(image.Uri.ToString());
    }
}

  2. 0

    Why don’t you add another property for the string and mark ProductImage with [JsonIgnore]?

    public string ProductImageString { get; set; }

[JsonIgnore]
public ImageSource ProductImage
{
    get => ImageSource.FromString(ProductImageString);
    set => ProductImageString = value.ToString();
}

    Note: get with ImageSource.FromString is just an example. Use whatever method you have if you want to read the ImageSource back from your string.

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