[camera] Ensure that channel.invokeMethod runs on the main thread (fl…

…utter#3444)

packages/camera/camera/CHANGELOG.md

@@ -15,7 +15,7 @@
 
 ## 0.6.4+2
 
-* Set ImageStreamReader listener to null to prevent stale images when streaming images. 
+* Set ImageStreamReader listener to null to prevent stale images when streaming images.
 
 ## 0.6.4+1
 
@@ -75,7 +75,7 @@ As part of implementing federated architecture and making the interface compatib
 
 Method changes in `CameraController`:
 - The `takePicture` method no longer accepts the `path` parameter, but instead returns the captured image as an instance of the `XFile` class;
-- The `startVideoRecording` method no longer accepts the `filePath`. Instead the recorded video is now returned as a `XFile` instance when the `stopVideoRecording` method completes; 
+- The `startVideoRecording` method no longer accepts the `filePath`. Instead the recorded video is now returned as a `XFile` instance when the `stopVideoRecording` method completes;
 - The `stopVideoRecording` method now returns the captured video when it completes;
 - Added the `buildPreview` method which is now used to implement the CameraPreview widget.
 

packages/camera/camera/android/src/main/java/io/flutter/plugins/camera/DartMessenger.java

@@ -1,5 +1,7 @@
 package io.flutter.plugins.camera;
 
+import android.os.Handler;
+import android.os.Looper;
 import android.text.TextUtils;
 import androidx.annotation.Nullable;
 import io.flutter.plugin.common.BinaryMessenger;
@@ -56,14 +58,39 @@ void sendCameraErrorEvent(@Nullable String description) {
         });
   }
 
-  void send(EventType eventType) {
+  void send(CameraEventType eventType) {
+    send(eventType, new HashMap<>());
+  }
+
+  void send(CameraEventType eventType, Map<String, Object> args) {
+    if (cameraChannel == null) {
+      return;
+    }
+    new Handler(Looper.getMainLooper())
+        .post(
+            new Runnable() {
+              @Override
+              public void run() {
+                cameraChannel.invokeMethod(eventType.method, args);
+              }
+            });
+  }
+
+  void send(DeviceEventType eventType) {
     send(eventType, new HashMap<>());
   }
 
   void send(EventType eventType, Map<String, Object> args) {
     if (channel == null) {
       return;
     }
-    channel.invokeMethod(eventType.toString().toLowerCase(), args);
+    new Handler(Looper.getMainLooper())
+        .post(
+            new Runnable() {
+              @Override
+              public void run() {
+                deviceChannel.invokeMethod(eventType.method, args);
+              }
+            });
   }
 }