# MapFieldCodec<TKey, TValue>.WriteField(Writer<TBufferWriter>, uint, Type, MapField<TKey, TValue>)

[Type overview](/orleans/docs/api/csharp/microsoft.orleans.serialization.protobuf/orleans.serialization.mapfieldcodec-2/) | [Methods](/orleans/docs/api/csharp/microsoft.orleans.serialization.protobuf/orleans.serialization.mapfieldcodec-2/methods/)

[Source](https://github.com/dotnet/orleans/blob/e4e752cedecc2976811db49802c7a999b1f1c704/src/Serializers/Orleans.Serialization.Protobuf/MapFieldCodec.cs#L43-L63)

```csharp
public void MapFieldCodec<TKey, WriteField<TBufferWriter>(ref Writer<TBufferWriter> writer, uint fieldIdDelta, Type expectedType, MapField<TKey, TValue> value)
```

Writes a field.

### Parameters

- `writer` (`Writer<TBufferWriter>`): The writer.
- `fieldIdDelta` (`uint`): The field identifier delta.
- `expectedType` (`Type`): The expected type.
- `value` (`MapField<TKey, TValue>`): The value.