ElectronNET/Electron.NET · error · JsonException

Expected array for ModifierType list

Error message

Expected array for ModifierType list

What it means

ModifierTypeListConverter.Read is a System.Text.Json converter for List<ModifierType>. It requires the incoming JSON token to be a StartArray; anything else (number, string, object, null-token shapes) cannot be mapped to a modifier list and is rejected with a JsonException "Expected array for ModifierType list". It exists because ModifierType values arrive from Electron as a JSON array of strings.

Solutions

1. Send the value as a JSON array of strings: "modifiers": ["ctrl", "shift"].
2. Fix the JS/Electron side to pass an array (wrap single values: [modifier]).
3. Update the .NET model/converter if the upstream schema intentionally changed to a single-value shape.
4. Validate/normalize the payload before deserialization (if Array.isArray check on the JS side).

Example fix

// before
{ "modifiers": "ctrl" }
// after
{ "modifiers": ["ctrl"] }

if (payload.modifiers != null && !Array.isArray(payload.modifiers))
    payload.modifiers = [payload.modifiers]; // normalize before sending over IPC

function isModifierTypeList(v: unknown): v is string[] {
  return Array.isArray(v) && v.every(x => typeof x === 'string');
}

try
{
    var list = JsonSerializer.Deserialize<List<ModifierType>>(json, ElectronJson.Options);
}
catch (JsonException ex) when (ex.Message.Contains("Expected array for ModifierType list"))
{
    Logger.Error("'modifiers' must be a JSON array of strings, e.g. [\"ctrl\"].");
}

When it happens

Trigger: Deserializing JSON where a ModifierType list property holds a non-array value — e.g. "modifiers": "ctrl" (string) or "modifiers": 3 (number) or an object — while ElectronJson.Options applies ModifierTypeListConverter to that property.

Common situations: Electron/IPC payload schema changed or was hand-crafted with a single modifier instead of an array; JS side sent a comma-joined string; tests/fixtures using the wrong JSON shape; version mismatch between the Electron front-end payload and the .NET model.

Understand the failure class

Background: "is not a compatible type" / "cannot merge" errors: when a value's type doesn't match what the library requires — this error's family across 65 libraries.

Related errors

• Expected string enum value
• Invalid value for PageSize. Expected string or an object.
• Unsupported token
• Unexpected token when reading releaseNotes.
• Invalid value for TitleBarOverlay. Expected boolean or an…

AI-assisted analysis of ElectronNET/Electron.NET@87cc6f98b6 (2026-09-14). Data as JSON: /api/errors/7b634a8fd998ab17. Report an issue: GitHub.

Appendix: source

Thrown at src/ElectronNET.API/Converter/ModifierTypeListConverter.cs:24

using System.Text.Json;
using System.Text.Json.Serialization;

/// <summary>
/// 
/// </summary>
public class ModifierTypeListConverter : JsonConverter<List<ModifierType>>
{
    public override List<ModifierType> Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
        if (reader.TokenType == JsonTokenType.Null)
        {
            return null;
        }

        var list = new List<ModifierType>();
        if (reader.TokenType != JsonTokenType.StartArray)
        {
            throw new JsonException("Expected array for ModifierType list");
        }

        while (reader.Read())
        {
            if (reader.TokenType == JsonTokenType.EndArray) break;
            if (reader.TokenType != JsonTokenType.String) throw new JsonException("Expected string enum value");
            var s = reader.GetString();
            list.Add((ModifierType)Enum.Parse(typeof(ModifierType), s, ignoreCase: true));
        }

        return list;
    }

    public override void Write(Utf8JsonWriter writer, List<ModifierType> value, JsonSerializerOptions options)
    {
        writer.WriteStartArray();
        foreach (var modifier in value)
        {

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