本博客与 【Flutter】Flutter 混合开发 ( Flutter 与 Native 通信 | 在 Flutter 端实现 MethodChannel 通信 ) 博客相对应 , 该博客中开发 Flutter 的 Dart 端 ;
本博客中开发 Android 中的 Java 端 , 最终目标是二者可以进行信息交流 ;
Android 端 Java 中 , MethodChannel 构造函数方法原型如下 :
public class MethodChannel {
private static final String TAG = "MethodChannel#";
private final BinaryMessenger messenger;
private final String name;
private final MethodCodec codec;
/**
* Creates a new channel associated with the specified {@link BinaryMessenger} and with the
* specified name and the standard {@link MethodCodec}.
*
* @param messenger a {@link BinaryMessenger}.
* @param name a channel name String.
*/
public MethodChannel(BinaryMessenger messenger, String name) {
this(messenger, name, StandardMethodCodec.INSTANCE);
}
/**
* Creates a new channel associated with the specified {@link BinaryMessenger} and with the
* specified name and {@link MethodCodec}.
*
* @param messenger a {@link BinaryMessenger}.
* @param name a channel name String.
* @param codec a {@link MessageCodec}.
*/
public MethodChannel(BinaryMessenger messenger, String name, MethodCodec codec) {
if (BuildConfig.DEBUG) {
if (messenger == null) {
Log.e(TAG, "Parameter messenger must not be null.");
}
if (name == null) {
Log.e(TAG, "Parameter name must not be null.");
}
if (codec == null) {
Log.e(TAG, "Parameter codec must not be null.");
}
}
this.messenger = messenger;
this.name = name;
this.codec = codec;
}
}
BasicMessageChannel 接收
个参数 :
创建了 MethodChannel 实例对象后 , 如果要接收 Dart 端发送来的消息 , 需要设置 方法回调处理器 ;
调用 setMethodCallHandler 方法 , 可以为 MethodChannel 设置一个 方法回调处理器 ;
MethodChannel.setMethodCallHandler 函数原型如下 :
/**
* Registers a method call handler on this channel.
*
* <p>Overrides any existing handler registration for (the name of) this channel.
*
* <p>If no handler has been registered, any incoming method call on this channel will be handled
* silently by sending a null reply. This results in a <a
* href="https://api.flutter.dev/flutter/services/MissingPluginException-class.html">MissingPluginException</a>
* on the Dart side, unless an <a
* href="https://api.flutter.dev/flutter/services/OptionalMethodChannel-class.html">OptionalMethodChannel</a>
* is used.
*
* @param handler a {@link MethodCallHandler}, or null to deregister.
*/
@UiThread
public void setMethodCallHandler(final @Nullable MethodCallHandler handler) {
messenger.setMessageHandler(
name, handler == null ? null : new IncomingMethodCallHandler(handler));
}
设置的 final @Nullable MethodCallHandler handler 参数 , 就是 方法回调处理器 ;
在 MethodCallHandler 接口中 , 只有一个 onMethodCall 方法 , 该方法是用于接收 Dart 传递来的消息的 ;
void onMethodCall(@NonNull MethodCall call, @NonNull Result result);
onMethodCall 参数简介 :
MessageHandler 接口原型如下 :
/** A handler of incoming method calls. */
public interface MethodCallHandler {
/**
* Handles the specified method call received from Flutter.
*
* <p>Handler implementations must submit a result for all incoming calls, by making a single
* call on the given {@link Result} callback. Failure to do so will result in lingering Flutter
* result handlers. The result may be submitted asynchronously. Calls to unknown or
* unimplemented methods should be handled using {@link Result#notImplemented()}.
*
* <p>Any uncaught exception thrown by this method will be caught by the channel implementation
* and logged, and an error result will be sent back to Flutter.
*
* <p>The handler is called on the platform thread (Android main thread). For more details see
* <a href="https://github.com/flutter/engine/wiki/Threading-in-the-Flutter-Engine">Threading in
* the Flutter Engine</a>.
*
* @param call A {@link MethodCall}.
* @param result A {@link Result} used for submitting the result of the call.
*/
@UiThread
void onMethodCall(@NonNull MethodCall call, @NonNull Result result);
}
在 MethodCall 中 , 主要有两个成员变量 :
/** Command object representing a method call on a {@link MethodChannel}. */
public final class MethodCall {
/** The name of the called method. */
public final String method;
/**
* Arguments for the call.
*
* <p>Consider using {@link #arguments()} for cases where a particular run-time type is expected.
* Consider using {@link #argument(String)} when that run-time type is {@link Map} or {@link
* JSONObject}.
*/
public final Object arguments;
}
Result 接口中提供了
个方法 , 根据不同的结果 , 回调不同的接口方法 ;
/**
* Method call result callback. Supports dual use: Implementations of methods to be invoked by
* Flutter act as clients of this interface for sending results back to Flutter. Invokers of
* Flutter methods provide implementations of this interface for handling results received from
* Flutter.
*
* <p>All methods of this class must be called on the platform thread (Android main thread). For
* more details see <a
* href="https://github.com/flutter/engine/wiki/Threading-in-the-Flutter-Engine">Threading in the
* Flutter Engine</a>.
*/
public interface Result {
/**
* Handles a successful result.
*
* @param result The result, possibly null. The result must be an Object type supported by the
* codec. For instance, if you are using {@link StandardMessageCodec} (default), please see
* its documentation on what types are supported.
*/
@UiThread
void success(@Nullable Object result);
/**
* Handles an error result.
*
* @param errorCode An error code String.
* @param errorMessage A human-readable error message String, possibly null.
* @param errorDetails Error details, possibly null. The details must be an Object type
* supported by the codec. For instance, if you are using {@link StandardMessageCodec}
* (default), please see its documentation on what types are supported.
*/
@UiThread
void error(String errorCode, @Nullable String errorMessage, @Nullable Object errorDetails);
/** Handles a call to an unimplemented method. */
@UiThread
void notImplemented();
}
Android 端实现 MethodChannel 通信步骤 :
首先 , 初始化 MethodChannel 实例对象 ;
MethodChannel mMethodChannel = new MethodChannel(mFlutterFragment.getFlutterEngine().getDartExecutor(), "MethodChannel");
然后 , 为 MethodChannel 实例对象 设置 MethodChannel.MethodCallHandler , 用于接收 Flutter 端调用 Android 端方法 ;
mMethodChannel.setMethodCallHandler(new MethodChannel.MethodCallHandler() {
@Override
public void onMethodCall(@NonNull MethodCall call, @NonNull MethodChannel.Result result) {
show_message.setText("Dart 端通过 MethodChannel 调用 Android 端的 " + call.method + " 方法 , 参数是 " + call.arguments);
}
});
最后 , 调用 mMethodChannel 的 invokeMethod 方法 , 调用 Flutter 中的方法 ;
findViewById(R.id.channel3).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
mMethodChannel.invokeMethod("method", "arguments");
}
});
参考资料 :
重要的专题 :
博客源码下载 :
- **Flutter Module 工程 :** [https://github.com/han1202012/flutter\_module](https://github.com/han1202012/flutter_module)
- **Android 应用 :** [https://github.com/han1202012/flutter\_native](https://github.com/han1202012/flutter_native)
- **注意 : 上面两个工程要放在同一个目录中 , 否则编译不通过 ;**