System.Text.Json.JsonSerializer' threw an exception. ---> System.MissingMethodException

[eltra-ch]

just updated to visual studio 16.9.1, Visual Studio for Mac 8.9 (build 1651). Latest Xamarin Forms 5.0.0.2012 etc.

by calling Serialize using System.Text.Json.Serializer of simple class (UserIdentity) below:

I get following exception:

System.TypeInitializationException: The type initializer for 'System.Text.Json.JsonSerializer' threw an exception. ---> System.MissingMethodException: Method not found: int System.Text.Encodings.Web.TextEncoder.FindFirstCharacterToEncodeUtf8(System.ReadOnlySpan1<byte>) at System.Text.Json.JsonEncodedText.EncodeHelper (System.ReadOnlySpan1[T] utf8Value, System.Text.Encodings.Web.JavaScriptEncoder encoder) [0x00000] in <7e3a59f5e4004edbb4b17c580799cc52>:0
at System.Text.Json.JsonEncodedText.TranscodeAndEncode (System.ReadOnlySpan1[T] value, System.Text.Encodings.Web.JavaScriptEncoder encoder) [0x00033] in <7e3a59f5e4004edbb4b17c580799cc52>:0 at System.Text.Json.JsonEncodedText.Encode (System.ReadOnlySpan1[T] value, System.Text.Encodings.Web.JavaScriptEncoder encoder) [0x00014] in <7e3a59f5e4004edbb4b17c580799cc52>:0
at System.Text.Json.JsonEncodedText.Encode (System.String value, System.Text.Encodings.Web.JavaScriptEncoder encoder) [0x00014] in <7e3a59f5e4004edbb4b17c580799cc52>:0
at System.Text.Json.JsonSerializer..cctor () [0x00042] in <7e3a59f5e4004edbb4b17c580799cc52>:0
--- End of inner exception stack trace ---

This was working fine in previous releases!

[DataContract]
public class UserIdentity
{
///

/// UserIdentity
///

public UserIdentity()
{
Header = DefaultHeader;
}

    #region Properties

    /// <summary>
    /// DefaultHeader
    /// </summary>
    public static string DefaultHeader = "ABA0";

    /// <summary>
    /// Header
    /// </summary>
    [DataMember]
    public string Header { get; set; }

    /// <summary>
    /// Login
    /// </summary>
    [DataMember]
    [Required]
    [EmailAddress]
    public string Login { get; set; }

    /// <summary>
    /// Name
    /// </summary>
    [DataMember]
    public string Name { get; set; }

    /// <summary>
    /// Password
    /// </summary>
    [DataMember]
    [Required]
    [DataType(DataType.Password)]
    public string Password { get; set; }

    /// <summary>
    /// User role
    /// </summary>
    [DataMember]
    public string Role { get; set; }

    /// <summary>
    /// Is valid
    /// </summary>
    [IgnoreDataMember]
    [JsonIgnore]
    public bool IsValid
    {
        get
        {
            return !string.IsNullOrEmpty(Login) && !string.IsNullOrEmpty(Password);
        }
    }

    #endregion
}

[filipnavara]

The underlying issue: mono/mono#20805
Workaround is presented there.

[eltra-ch]

Workaround doesn't work in my case. I applied 1:1 the references, but now I cannot use the "ReadOnlySpan" and "Span" classes. I don't know if this playes any role, but the those classes are used over .net standard 2.0 library.

[filipnavara]

We also use .NET Standard 2.0 libraries. In the Xamarin main project we use the overrides for System.Buffers/System.Memory to convince NuGet that the dependency is satisfied without overwriting the actual files coming from the Mono/Xamarin framework.

[spouliot]

Dupe of #10548