【移动端】Flutter 获取Android AMap实例

背景

本文的背景，是因为我在开发高德地图时，需要自定义高德比例尺位置和样式；但结果查看了AMap Flutter插件和AMap SDK源码后，发现AMap无法添加自定义MyMethodCallHandler的实现类！

why？

源码

在Flutter中，高德地图的每个地图视图都是通过AMapPlatformView类生成且管理的，源码如下

package com.amap.flutter.map;import android.content.Context;
import android.os.Bundle;
import android.view.View;import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.lifecycle.DefaultLifecycleObserver;
import androidx.lifecycle.LifecycleOwner;import com.amap.api.maps.AMap;
import com.amap.api.maps.AMapOptions;
import com.amap.api.maps.TextureMapView;
import com.amap.flutter.map.core.MapController;
import com.amap.flutter.map.overlays.marker.MarkersController;
import com.amap.flutter.map.overlays.polygon.PolygonsController;
import com.amap.flutter.map.overlays.polyline.PolylinesController;
import com.amap.flutter.map.utils.LogUtil;import java.util.HashMap;
import java.util.Map;import io.flutter.embedding.engine.plugins.activity.ActivityPluginBinding;
import io.flutter.plugin.common.BinaryMessenger;
import io.flutter.plugin.common.MethodCall;
import io.flutter.plugin.common.MethodChannel;
import io.flutter.plugin.platform.PlatformView;/*** @author whm* @date 2020/10/27 5:49 PM* @mail [e-mail]* @since*/
public class AMapPlatformViewimplementsDefaultLifecycleObserver,ActivityPluginBinding.OnSaveInstanceStateListener,MethodChannel.MethodCallHandler,PlatformView {private static final String CLASS_NAME = "AMapPlatformView";private final MethodChannel methodChannel;private MapController mapController;private MarkersController markersController;private PolylinesController polylinesController;private PolygonsController polygonsController;private TextureMapView mapView;private boolean disposed = false;private final Map<String, MyMethodCallHandler> myMethodCallHandlerMap;AMapPlatformView(int id,Context context,BinaryMessenger binaryMessenger,LifecycleProvider lifecycleProvider,AMapOptions options) {methodChannel = new MethodChannel(binaryMessenger, "amap_flutter_map_" + id);methodChannel.setMethodCallHandler(this);myMethodCallHandlerMap = new HashMap<String, MyMethodCallHandler>(8);try {mapView = new TextureMapView(context, options);AMap amap = mapView.getMap();mapController = new MapController(methodChannel, mapView);markersController = new MarkersController(methodChannel, amap);polylinesController = new PolylinesController(methodChannel, amap);polygonsController = new PolygonsController(methodChannel, amap);initMyMethodCallHandlerMap();lifecycleProvider.getLifecycle().addObserver(this);} catch (Throwable e) {LogUtil.e(CLASS_NAME, "<init>", e);}}private void initMyMethodCallHandlerMap() {String[] methodIdArray = mapController.getRegisterMethodIdArray();if (null != methodIdArray && methodIdArray.length > 0) {for (String methodId : methodIdArray) {myMethodCallHandlerMap.put(methodId, mapController);}}methodIdArray = markersController.getRegisterMethodIdArray();if (null != methodIdArray && methodIdArray.length > 0) {for (String methodId : methodIdArray) {myMethodCallHandlerMap.put(methodId, markersController);}}methodIdArray = polylinesController.getRegisterMethodIdArray();if (null != methodIdArray && methodIdArray.length > 0) {for (String methodId : methodIdArray) {myMethodCallHandlerMap.put(methodId, polylinesController);}}methodIdArray = polygonsController.getRegisterMethodIdArray();if (null != methodIdArray && methodIdArray.length > 0) {for (String methodId : methodIdArray) {myMethodCallHandlerMap.put(methodId, polygonsController);}}}public MapController getMapController() {return mapController;}public MarkersController getMarkersController() {return markersController;}public PolylinesController getPolylinesController() {return polylinesController;}public PolygonsController getPolygonsController() {return polygonsController;}@Overridepublic void onMethodCall(@NonNull MethodCall call, @NonNull MethodChannel.Result result) {LogUtil.i(CLASS_NAME, "onMethodCall==>" + call.method + ", arguments==> " + call.arguments);String methodId = call.method;if (myMethodCallHandlerMap.containsKey(methodId)) {myMethodCallHandlerMap.get(methodId).doMethodCall(call, result);} else {LogUtil.w(CLASS_NAME, "onMethodCall, the methodId: " + call.method + ", not implemented");result.notImplemented();}}@Overridepublic void onCreate(@NonNull LifecycleOwner owner) {LogUtil.i(CLASS_NAME, "onCreate==>");try {if (disposed) {return;}if (null != mapView) {mapView.onCreate(null);}} catch (Throwable e) {LogUtil.e(CLASS_NAME, "onCreate", e);}}@Overridepublic void onStart(@NonNull LifecycleOwner owner) {LogUtil.i(CLASS_NAME, "onStart==>");}@Overridepublic void onResume(@NonNull LifecycleOwner owner) {LogUtil.i(CLASS_NAME, "onResume==>");try {if (disposed) {return;}if (null != mapView) {mapView.onResume();}} catch (Throwable e) {LogUtil.e(CLASS_NAME, "onResume", e);}}@Overridepublic void onPause(@NonNull LifecycleOwner owner) {LogUtil.i(CLASS_NAME, "onPause==>");try {if (disposed) {return;}mapView.onPause();} catch (Throwable e) {LogUtil.e(CLASS_NAME, "onPause", e);}}@Overridepublic void onStop(@NonNull LifecycleOwner owner) {LogUtil.i(CLASS_NAME, "onStop==>");}@Overridepublic void onDestroy(@NonNull LifecycleOwner owner) {LogUtil.i(CLASS_NAME, "onDestroy==>");try {if (disposed) {return;}destroyMapViewIfNecessary();} catch (Throwable e) {LogUtil.e(CLASS_NAME, "onDestroy", e);}}@Overridepublic void onSaveInstanceState(@NonNull Bundle bundle) {LogUtil.i(CLASS_NAME, "onDestroy==>");try {if (disposed) {return;}mapView.onSaveInstanceState(bundle);} catch (Throwable e) {LogUtil.e(CLASS_NAME, "onSaveInstanceState", e);}}@Overridepublic void onRestoreInstanceState(@Nullable Bundle bundle) {LogUtil.i(CLASS_NAME, "onDestroy==>");try {if (disposed) {return;}mapView.onCreate(bundle);} catch (Throwable e) {LogUtil.e(CLASS_NAME, "onRestoreInstanceState", e);}}@Overridepublic View getView() {LogUtil.i(CLASS_NAME, "getView==>");return mapView;}@Overridepublic void dispose() {LogUtil.i(CLASS_NAME, "dispose==>");try {if (disposed) {return;}methodChannel.setMethodCallHandler(null);destroyMapViewIfNecessary();disposed = true;} catch (Throwable e) {LogUtil.e(CLASS_NAME, "dispose", e);}}private void destroyMapViewIfNecessary() {if (mapView == null) {return;}mapView.onDestroy();}}

分析

通过上面的源码可以发现如下几点：

1. 在它onMethodCall回调方法中，判断了方法名是否在myMethodCallHandlerMap中存在

@Overridepublic void onMethodCall(@NonNull MethodCall call, @NonNull MethodChannel.Result result) {LogUtil.i(CLASS_NAME, "onMethodCall==>" + call.method + ", arguments==> " + call.arguments);String methodId = call.method;if (myMethodCallHandlerMap.containsKey(methodId)) {myMethodCallHandlerMap.get(methodId).doMethodCall(call, result);} else {LogUtil.w(CLASS_NAME, "onMethodCall, the methodId: " + call.method + ", not implemented");result.notImplemented();}}

2. myMethodCallHandlerMap 是一个final属性，这也就意味着，它在构造函数中已经实例化了，且不能更改值，只能修改内容，它通过initMyMethodCallHandlerMap注册所有的Hnadler

private final Map<String, MyMethodCallHandler> myMethodCallHandlerMap;AMapPlatformView(int id,Context context,BinaryMessenger binaryMessenger,LifecycleProvider lifecycleProvider,AMapOptions options) {methodChannel = new MethodChannel(binaryMessenger, "amap_flutter_map_" + id);methodChannel.setMethodCallHandler(this);myMethodCallHandlerMap = new HashMap<String, MyMethodCallHandler>(8);try {mapView = new TextureMapView(context, options);AMap amap = mapView.getMap();mapController = new MapController(methodChannel, mapView);markersController = new MarkersController(methodChannel, amap);polylinesController = new PolylinesController(methodChannel, amap);polygonsController = new PolygonsController(methodChannel, amap);initMyMethodCallHandlerMap();lifecycleProvider.getLifecycle().addObserver(this);} catch (Throwable e) {LogUtil.e(CLASS_NAME, "<init>", e);}
}

3. 通过initMyMethodCallHandlerMap方法可以看出，它只注册了mapController、markersController、polylinesController、polygonsController四类Handler，且没有提供可以自定义注册的方法，所以我也无能为力了

private void initMyMethodCallHandlerMap() {String[] methodIdArray = mapController.getRegisterMethodIdArray();if (null != methodIdArray && methodIdArray.length > 0) {for (String methodId : methodIdArray) {myMethodCallHandlerMap.put(methodId, mapController);}}methodIdArray = markersController.getRegisterMethodIdArray();if (null != methodIdArray && methodIdArray.length > 0) {for (String methodId : methodIdArray) {myMethodCallHandlerMap.put(methodId, markersController);}}methodIdArray = polylinesController.getRegisterMethodIdArray();if (null != methodIdArray && methodIdArray.length > 0) {for (String methodId : methodIdArray) {myMethodCallHandlerMap.put(methodId, polylinesController);}}methodIdArray = polygonsController.getRegisterMethodIdArray();if (null != methodIdArray && methodIdArray.length > 0) {for (String methodId : methodIdArray) {myMethodCallHandlerMap.put(methodId, polygonsController);}}}

解决思路

1. 通过修改initMyMethodCallHandlerMap属性值（不推荐）

通过上面分析可以想到，通过修改initMyMethodCallHandlerMap属性值，自定义handler，但前提时需要拿到对应的AMapPlatformView实例，通常的方法可以通过ServiceLoader来获取，但在Android中ServiceLoader是不用生效的，Android环境中必须通过PathClassLoader、DexClassLoader来加载类，具体加载方法，可以参考其他大神的博客，我这里不做过多追述，因为我不推荐

2. 通过PlatformViewsController来获取视图（推荐）

推荐这个方法是因为它可以i通过mapId直接获取，且不用过多介入到内存和进程中的交互中

1. 创建一个自定义MethodChannel

var methodChannel = MethodChannel(flutterEngine.dartExecutor.binaryMessenger, "method_channel_id")methodChannel.setMethodCallHandler { call, result ->run {//....}}

2. AMapPlatformView继承PlatformView，所以可以通过FlutterEngine.getPlatformViewsController().getPlatformViewById(viewId)方式获取，获取到的是TextureMapView视图，TextureMapView.getMap()可以获取AMap类，从而实现对当前地图视图进行任何操作，

class MainActivity : FlutterActivity() {var handerControllerMap = HashMap<String, IMyMethodCallHander>();override fun configureFlutterEngine(flutterEngine: FlutterEngine) {super.configureFlutterEngine(flutterEngine)IFlutterFactory.engine=flutterEngine;}
}

/*** 当前缩放级别下，地图上1像素点对应的长度，单位米。* @param call* @param result*/public void getScalePerPixel(MethodCall call, MethodChannel.Result result) {Object mapId = call.argument("mapId");if (null == call || null == mapId) {return;}try {View view = IFlutterFactory.engine.getPlatformViewsController().getPlatformViewById(Integer.parseInt(mapId.toString()));if (view != null) {result.success(((TextureMapView) view).getMap().getScalePerPixel());} else {result.error("ScaleControllerExecption", "获取比例尺数据失败！", "");}} catch (Exception e) {result.error("ScaleControllerExecption", e.getMessage(), e.getLocalizedMessage());}}

3. viewId 其实就是mapId，可以通过AMapController.mapId获取，而AMapController可以通过AMapWidget的onMapCreated的回调方法获取

void onMapCreated(AMapController controller) {//连接自定义的MethodChannelMethodChannel _channel=MethodChannel("method_channel_id");//将mapId传给android端double? scale=await _channel.invokeMethod<double>("scale#get",<String,dynamic>{"mapId":_mapController.mapId});print('-----scale---$scale');
}