如何使用 MethodChannel 从本机平台调用应用程序的 Dart 部分中的方法? [英] How to call methods in Dart portion of the app, from the native platform using MethodChannel?

问题描述

我正在编写一个原生插件，在某些情况下，它必须调用应用程序的 Flutter 部分中的函数，用 Dart 编写.它是如何实现的，解释如下:https://flutter.io/platform-channels/

I am writing a native plugin that, in some cases, has to call functions in the Flutter portion of the app, written in Dart. How it's achieved, is explained here: https://flutter.io/platform-channels/

此外，这里有一个从原生/平台部分向 Dart/非原生调用方法的示例:https://github.com/flutter/plugins/tree/master/packages/quick_actions

Furthermore, an example of invoking a method from the native/platform part towards the Dart/non-native is here: https://github.com/flutter/plugins/tree/master/packages/quick_actions

现在，这个例子非常好，以防平台只需要调用一个method，即该调用不返回任何内容/void，但万一它需要调用一个 function，即需要来自非本机/Dart 部分的返回值，我在互联网上找不到示例或文档.不过我相信它是可以实现的，因为在原生 Java 部分，有一个方法:

Now, this example is really nice in case the platform only needs to invoke a method, i.e. that call returns nothing/void, but in case it needs to invoke a function, i.e. needs a return value from the non-native/Dart part, I could not have found an example or documentation on the internet. I believe it can be implemented though, because in the native Java part, there is a method:

public void invokeMethod(String method, Object arguments, MethodChannel.Result callback)

所以，有一个 callback 对象可能有来自非本地部分的返回值 - 或者，我在这里弄错了，目前没有办法从非本地部分返回值- 应用的原生 Dart 部分?

So, there is a callback object that could have a return value from the non-native part - or, I am mistaken here, and there is currently no way of returning a value from the non-native Dart portion of the app?

推荐答案

签名是void setMethodCallHandler(Future handler(MethodCall call))，所以我们需要在返回 Future 的 Dart 端，例如 _channel.setMethodCallHandler(myUtilsHandler);

The signature is void setMethodCallHandler(Future<dynamic> handler(MethodCall call)), so we need to provide a function at the Dart end that returns Future<dynamic>, for example _channel.setMethodCallHandler(myUtilsHandler);

然后实现处理程序.这个处理两个方法 foo 和 bar 分别返回 String 和 double.

Then implement the handler. This one handles two methods foo and bar returning respectively String and double.

  Future<dynamic> myUtilsHandler(MethodCall methodCall) async {
    switch (methodCall.method) {
      case 'foo':
        return 'some string';
      case 'bar':
        return 123.0;
      default:
        throw MissingPluginException('notImplemented');
    }
  }

在Java端，返回值被传递给Result回调的success方法.

At the Java end the return value is passed to the success method of the Result callback.

channel.invokeMethod("foo", arguments, new Result() {
  @Override
  public void success(Object o) {
    // this will be called with o = "some string"
  }

  @Override
  public void error(String s, String s1, Object o) {}

  @Override
  public void notImplemented() {}
});

在 Swift 中，返回值是传递给 result 闭包的 Any?.(未实现由任何参数表示为 const NSObject 值 FlutterMethodNotImplemented.)

In Swift, the return value is an Any? passed to the result closure. (Not implemented is signaled by the any parameter being the const NSObject value FlutterMethodNotImplemented.)

channel.invokeMethod("foo", arguments: args, result: {(r:Any?) -> () in
  // this will be called with r = "some string" (or FlutterMethodNotImplemented)
})

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