Extracted per-camera channel construction out into CameraPlugin for t…

…esting purposes.

packages/camera/android/src/main/java/dev/flutter/plugins/camera/AndroidCameraSystem.java

@@ -13,7 +13,6 @@
 
 import java.io.IOException;
 import java.util.ArrayList;
-import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 
@@ -22,6 +21,9 @@
 import io.flutter.plugin.common.EventChannel;
 import io.flutter.view.TextureRegistry;
 
+/**
+ * Android implementation of a {@link CameraSystem}.
+ */
 /* package */ class AndroidCameraSystem implements CameraSystem {
   @NonNull
   private final FlutterPlugin.FlutterPluginBinding pluginBinding;
@@ -31,19 +33,23 @@
   private final CameraPermissions cameraPermissions;
   @NonNull
   private final CameraPreviewDisplay cameraPreviewDisplay;
+  @NonNull
+  private final CameraPluginProtocol.CameraEventChannelFactory cameraEventChannelFactory;
   @Nullable
   private Camera camera;
 
   /* package */ AndroidCameraSystem(
       @NonNull FlutterPlugin.FlutterPluginBinding pluginBinding,
       @NonNull ActivityPluginBinding activityBinding,
       @NonNull CameraPermissions cameraPermissions,
-      @NonNull CameraPreviewDisplay cameraPreviewDisplay
-  ) {
+      @NonNull CameraPreviewDisplay cameraPreviewDisplay,
+      @NonNull CameraPluginProtocol.CameraEventChannelFactory cameraEventChannelFactory
+      ) {
     this.pluginBinding = pluginBinding;
     this.activityBinding = activityBinding;
     this.cameraPermissions = cameraPermissions;
     this.cameraPreviewDisplay = cameraPreviewDisplay;
+    this.cameraEventChannelFactory = cameraEventChannelFactory;
   }
 
   @Override
@@ -118,36 +124,19 @@ public void onCameraOpenFailed(@NonNull String message) {
       }
     });
 
-    EventChannel cameraEventChannel = new EventChannel(
-        pluginBinding.getFlutterEngine().getDartExecutor(),
-        "flutter.io/cameraPlugin/cameraEvents" + textureEntry.id()
-    );
+    final CameraPluginProtocol.ChannelCameraEventHandler eventHandler = new CameraPluginProtocol.ChannelCameraEventHandler();
+    camera.setCameraEventHandler(eventHandler);
+
+    EventChannel cameraEventChannel = cameraEventChannelFactory.createCameraEventChannel(textureEntry.id());
     cameraEventChannel.setStreamHandler(new EventChannel.StreamHandler() {
       @Override
       public void onListen(Object o, final EventChannel.EventSink eventSink) {
-        final Camera.CameraEventHandler cameraEventHandler = new Camera.CameraEventHandler() {
-          @Override
-          public void onError(String description) {
-            Map<String, String> event = new HashMap<>();
-            event.put("eventType", "error");
-            event.put("errorDescription", description);
-            eventSink.success(event);
-          }
-
-          @Override
-          public void onCameraClosed() {
-            Map<String, String> event = new HashMap<>();
-            event.put("eventType", "camera_closing");
-            eventSink.success(event);
-          }
-        };
-
-        camera.setCameraEventHandler(cameraEventHandler);
+        eventHandler.setEventSink(eventSink);
       }
 
       @Override
       public void onCancel(Object o) {
-        camera.setCameraEventHandler(null);
+        eventHandler.setEventSink(null);
       }
     });
   }

packages/camera/android/src/main/java/dev/flutter/plugins/camera/CameraImageStream.java

@@ -8,6 +8,9 @@
 
 import androidx.annotation.NonNull;
 
+/**
+ * Serializes and sends an {@link Image} to a destination through a stream.
+ */
 public interface CameraImageStream {
   void sendImage(@NonNull Image image);
 }

packages/camera/android/src/main/java/dev/flutter/plugins/camera/CameraPlugin.java

@@ -73,26 +73,32 @@ private void setup() {
         "plugins.flutter.io/camera/imageStream"
     );
     CameraPreviewDisplay cameraImageStream = new CameraPluginProtocol.ChannelCameraPreviewDisplay(imageStreamChannel);
+    CameraPluginProtocol.CameraEventChannelFactory cameraChannelFactory = new CameraPluginProtocol.CameraEventChannelFactory() {
+      @NonNull
+      @Override
+      public EventChannel createCameraEventChannel(long textureId) {
+        return new EventChannel(
+            pluginBinding.getFlutterEngine().getDartExecutor(),
+            "flutter.io/cameraPlugin/cameraEvents" + textureId
+        );
+      }
+    };
     CameraSystem cameraSystem = new AndroidCameraSystem(
         pluginBinding,
         activityBinding,
         cameraPermissions,
-        cameraImageStream
+        cameraImageStream,
+        cameraChannelFactory
     );
     this.cameraPluginProtocol = new CameraPluginProtocol(cameraSystem);
 
-    final MethodChannel channel = new MethodChannel(
+    final MethodChannel primaryPluginChannel = new MethodChannel(
         pluginBinding.getFlutterEngine().getDartExecutor(),
         "plugins.flutter.io/camera"
     );
-    channel.setMethodCallHandler(cameraPluginProtocol.getCameraSystemChannelHandler());
+    primaryPluginChannel.setMethodCallHandler(cameraPluginProtocol.getCameraSystemChannelHandler());
   }
 
-  // TODO: there are 2+ channels
-  // 1:EventChannel   - plugins.flutter.io/camera/imageStream
-  // 1:MethodChannel  - plugins.flutter.io/camera
-  // 0+:EventChannel  - flutter.io/cameraPlugin/cameraEvents[textureId]
-
   private void teardown() {
     // Teardown
     if (Build.VERSION.SDK_INT < Build.VERSION_CODES.LOLLIPOP) {

packages/camera/android/src/main/java/dev/flutter/plugins/camera/CameraPluginProtocol.java

@@ -8,12 +8,14 @@
 import android.media.Image;
 
 import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
 
 import java.nio.ByteBuffer;
 import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.concurrent.CopyOnWriteArrayList;
 
 import io.flutter.plugin.common.EventChannel;
 import io.flutter.plugin.common.MethodCall;
@@ -286,6 +288,11 @@ private void handleException(Exception exception, MethodChannel.Result result) {
     }
   }
 
+  interface CameraEventChannelFactory {
+    @NonNull
+    EventChannel createCameraEventChannel(long textureId);
+  }
+
   /**
    * Implementation of a {@link CameraPreviewDisplay} that uses an {@link EventChannel}
    * to send camera preview images to Flutter.
@@ -352,4 +359,45 @@ public void sendImage(@NonNull Image image) {
       imageStreamSink.success(imageBuffer);
     }
   }
+
+  /* package */ static class ChannelCameraEventHandler implements Camera.CameraEventHandler {
+    private final List<Map<String, String>> queuedEvents = new CopyOnWriteArrayList<>();
+    private EventChannel.EventSink eventSink;
+
+    /* package */ ChannelCameraEventHandler() {}
+
+    public void setEventSink(@Nullable EventChannel.EventSink eventSink) {
+      this.eventSink = eventSink;
+
+      // Send all queue'd events.
+      if (!queuedEvents.isEmpty()) {
+        while (!queuedEvents.isEmpty()) {
+          eventSink.success(queuedEvents.remove(0));
+        }
+      }
+    }
+
+    @Override
+    public void onError(String description) {
+      Map<String, String> event = new HashMap<>();
+      event.put("eventType", "error");
+      event.put("errorDescription", description);
+      sendEvent(event);
+    }
+
+    @Override
+    public void onCameraClosed() {
+      Map<String, String> event = new HashMap<>();
+      event.put("eventType", "camera_closing");
+      sendEvent(event);
+    }
+
+    private void sendEvent(@NonNull Map<String, String> event) {
+      if (eventSink != null) {
+        eventSink.success(event);
+      } else {
+        queuedEvents.add(event);
+      }
+    }
+  }
 }

packages/camera/android/src/main/java/dev/flutter/plugins/camera/CameraPreviewDisplay.java

@@ -6,6 +6,10 @@
 
 import androidx.annotation.NonNull;
 
+/**
+ * Displays a camera preview by streaming {@link Image}s from an Android
+ * camera by way of a given {@link ImageStreamConnection}.
+ */
 public interface CameraPreviewDisplay {
   void startStreaming(@NonNull final ImageStreamConnection connection);
 

packages/camera/android/src/main/java/dev/flutter/plugins/camera/CameraSystem.java

@@ -10,6 +10,9 @@
 
 import java.util.List;
 
+/**
+ * Top-level facade for all Camera plugin behavior.
+ */
 /* package */ interface CameraSystem {
   List<CameraDetails> getAvailableCameras() throws CameraAccessException;