How do I best give multiple arguments with the java version of flutters MethodChannel.invokeMenthod?

Question

I have a flutter project (plugin) that uses some native java code as well. To communicate between dart and java I use the MethodChannel.invokeMethod. This works very nicely from dart for java and I can pull out the named arguments with call.argument("name") in java. The other way is, however, giving me a bit of headache as I need to pass a variable number of arguments to dart with my method call, but invokeMethod only takes "Object" as an argument.

I have seen it work with just the single argument like a string or int, but I cannot seem to find a good way to implement it for multiple arguments.

I would have expected that there was some sort of list object type that I could pass as an argument for invokeMethod but I have not been able to find it anywhere.

Can any of you give a hint on how to best do this?

Answer 1

You have to pass a Map<String, dynamic> as the single object. (Note that each of the dynamics must be one of the allowed data types.) This appears at the Java end as a HashMap. There are useful getter functions at the Java end to access the hash map members.

Dart

  static void foo(String bar, bool baz) {
    _channel.invokeMethod('foo', <String, dynamic>{
      'bar': bar,
      'baz': baz,
    });
  }

Java

  String bar = call.argument("bar"); // .argument returns the correct type
  boolean baz = call.argument("baz"); // for the assignment

Using this answer for the full outline, you can achieve the opposite direction like:

Java

  static void charlie(String alice, boolean bob) {
    HashMap<String, Object> arguments = new HashMap<>();
    arguments.put("alice", alice);
    arguments.put("bob", bob);
    channel.invokeMethod("charlie", arguments);
  }

Dart

    String alice = methodCall.arguments['alice'];
    bool bob = methodCall.arguments['bob'];