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pigeon: implement primitive enum return values and arguments #87307
Description
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For Dart and Android, support for this feature is pretty straightforward. It can be solved by just updating the codec with enum indexes:
Dart:
enum Fruit { apple, banana, } class ACodec extends StandardMessageCodec { const ACodec(); @override void writeValue(WriteBuffer buffer, Object? value) { if (value is Fruit) { buffer.putUint8(128); writeValue(buffer, value.index); } else { super.writeValue(buffer, value); } } @override Object? readValueOfType(int type, ReadBuffer buffer) { switch (type) { case 128: return Fruit.values[readValue(buffer)! as int]; default: return super.readValueOfType(type, buffer); } } }
Java:
public enum Fruit { apple(0), banana(1); private int index; Fruit(final int index) { this.index = index; } } private static class ACodec extends StandardMessageCodec { public static final ACodec INSTANCE = new ACodec(); private ACodec() {} @Override protected Object readValueOfType(byte type, ByteBuffer buffer) { switch (type) { case (byte)128: return Fruit.values()[(int) readValue(buffer)]; default: return super.readValueOfType(type, buffer); } } @Override protected void writeValue(ByteArrayOutputStream stream, Object value) { if (value instanceof Fruit) { stream.write(128); writeValue(stream, ((Fruit) value).index); } else { super.writeValue(stream, value); } } }
But, the codec for Objective-C doesn't handle Objective-C type enums well. e.g:
typedef NS_ENUM(NSUInteger, Fruit) { FruitApple = 0, FruitBanana = 1, };
FlutterStandardReader.readValueOfTypeandFlutterStandardWriter.writeValuerequire an object, not a primitive, to be returned or passed respectively. So, the solution won't be as straightforward as other languages. A couple of solutions I came up with are:- [Breaking Change] The Objective-C generation could create Enum like classes with static variables. e.g.
@interface Fruit : NSObject @property(readonly) NSUInteger index; - (instancetype)init NS_UNAVAILABLE; + (Fruit *)apple; + (Fruit *)banana; @end
- Methods for
HostApis/FlutterApis could take and/or return enum wrappers. e.g.
typedef NS_ENUM(NSUInteger, Fruit) { FruitApple = 0, FruitBanana = 1, }; @interface FruitEnum : NSObject @property(readonly) Fruit value; - (instancetype)initWithValue:(Fruit)value; @end @protocol AClass - (void)aMethod:(NSArray<FruitEnum *> *)fruits error:(FlutterError *_Nullable *_Nonnull)error; @end
After merging flutter/packages#1871:
-
Enumargument works ✅:void bar(Foo foo);
-
List<Enum>argument does not work ❌:void bar(List<Foo> foo);
@gaaclarke is this intended?
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on Aug 28, 2023 This thread has been automatically locked since there has not been any recent activity after it was closed. If you are still experiencing a similar issue, please open a new bug, including the output of
flutter doctor -vand a minimal reproduction of the issue.- locked as resolved and limited conversation to collaborators
on Sep 11, 2023 - added a commit that references this issue
on Jun 10, 2026 - added a commit that references this issue
on Jun 19, 2026
example: