调用availableCameras()触发MissingPluginException问题求助

问题背景 #

测试带相机功能的Flutter应用时，调用availableCameras()仅在Android端报错，iOS端正常。该问题在添加自定义Native MethodChannel后出现。

报错信息 #

MissingPluginException (MissingPluginException(No implementation found for method availableCameras on channel plugins.flutter.io/camera_android))

调用代码 #

DartPluginRegistrant.ensureInitialized();
WidgetsFlutterBinding.ensureInitialized();
var cameras = await availableCameras();

已尝试的无效操作 #

• 降低camera包版本（测试过^0.10.0+4和0.9.7+1）
• 执行flutter clean + flutter pub get
• 重启VS Code和Android Studio
• 修改自定义MethodChannel名称（排查通道冲突）

相关配置与代码 #

pubspec.yaml #

dependencies:
  flutter:
    sdk: flutter

  camera: ^0.10.0+4
  # camera: 0.9.7+1
  path_provider: ^2.0.11
  path: ^1.8.2

# dependency_overrides:
  # camera_android: 0.9.7+1
  # camera_avfoundation: 0.9.7+1

Dart端自定义通道代码 #

class AppInfo {
  static const MethodChannel _channel = MethodChannel('appInfo');

  static Future<String?> get appVersion async {
    final String? version = await _channel.invokeMethod('getAppVersion');
    return version;
  }
}

Android端MainActivity.kt #

package com.xxx.xxxx

import android.content.pm.PackageManager
import androidx.annotation.NonNull
import io.flutter.embedding.android.FlutterActivity
import io.flutter.embedding.engine.FlutterEngine
import io.flutter.plugin.common.MethodChannel
import kotlinx.coroutines.ExperimentalCoroutinesApi

class MainActivity : FlutterActivity() {
    private val CHANNEL = "appInfo"

    @OptIn(ExperimentalCoroutinesApi::class)
    override fun configureFlutterEngine(@NonNull flutterEngine: FlutterEngine) {
        MethodChannel(
            flutterEngine.dartExecutor.binaryMessenger,
            CHANNEL
        ).setMethodCallHandler { call, result ->
            if (call.method == "getAppVersion") {
                try {
                    val pInfo =
                        applicationContext.packageManager.getPackageInfo(context.packageName, 0)
                    var version = pInfo.versionName
                    result.success("${pInfo.versionName}");

                } catch (e: PackageManager.NameNotFoundException) {
                    e.printStackTrace()
                    result.notImplemented()
                }
            } else {
                result.notImplemented()
            }
        }
    }
}

iOS端AppDelegate.swift #

import UIKit
import Flutter

@UIApplicationMain
@objc class AppDelegate: FlutterAppDelegate {
  override func application(
    _ application: UIApplication,
    didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
  ) -> Bool {
    GeneratedPluginRegistrant.register(with: self)

      let controller: FlutterViewController = window?.rootViewController as! FlutterViewController
      let helloMethodChannel = FlutterMethodChannel(name: "appInfo",binaryMessenger: controller as! FlutterBinaryMessenger)
      helloMethodChannel.setMethodCallHandler({
        (call:FlutterMethodCall,result:FlutterResult) -> Void in

        switch call.method{
            case "getAppVersion":
                result(Bundle.main.object(forInfoDictionaryKey:"CFBundleShortVersionString") as? String)
            default:
               result("iOS" + UIDevice.current.systemVersion)
        }

      })

    return super.application(application, didFinishLaunchingWithOptions: launchOptions)
  }
}

flutter doctor -v结果 #

[✓] Flutter (Channel stable, 3.3.6, on macOS 12.6 21G115 darwin-x64, locale en-JP)
    • Flutter version 3.3.6 on channel stable at /Users/ganessa/fvm/versions/stable
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision 6928314d50 (7 days ago), 2022-10-25 16:34:41 -0400
    • Engine revision 3ad69d7be3
    • Dart version 2.18.2
    • DevTools version 2.15.0

[✓] Android toolchain - develop for Android devices (Android SDK version 33.0.0)
    • Android SDK at /Users/ganessa/src/android-sdks
    • Platform android-33, build-tools 33.0.0
    • Java binary at: /Applications/Android Studio.app/Contents/jre/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build 11.0.12+0-b1504.28-7817840)
    • All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS (Xcode 13.4.1)
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Build 13F100
    • CocoaPods version 1.11.2

[✓] Chrome - develop for the web
    • Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome

[✓] Android Studio (version 2021.2)
    • Android Studio at /Applications/Android Studio.app/Contents
    • Flutter plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/9212-flutter
    • Dart plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/6351-dart
    • Java version OpenJDK Runtime Environment (build 11.0.12+0-b1504.28-7817840)

[✓] VS Code (version 1.72.2)
    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Flutter extension version 3.52.0

[✓] Connected device (4 available)
    • SHV43 (mobile)         • XXXXXXXXXXXXXXX           • android-arm64  • Android 9 (API 28)
    • iPhone SE2 MS (mobile) • XXXXXXXX-XXXXXXXXXXXXXXXX • ios            • iOS 15.6.1 19G82
    • macOS (desktop)        • macos                     • darwin-x64     • macOS 12.6 21G115 darwin-x64
    • Chrome (web)           • chrome                    • web-javascript • Google Chrome 107.0.5304.87

[✓] HTTP Host Availability
    • All required HTTP hosts are available

• No issues found!

可行排查/解决方法 #

1. 手动注册Android端相机插件
   在MainActivity的configureFlutterEngine方法中，优先注册相机插件，确保其初始化完成：

   import io.flutter.plugins.camera.CameraPlugin
   
   override fun configureFlutterEngine(@NonNull flutterEngine: FlutterEngine) {
       // 先注册相机插件
       CameraPlugin.registerWith(flutterEngine.dartExecutor.binaryMessenger)
       // 再注册自定义通道
       MethodChannel(flutterEngine.dartExecutor.binaryMessenger, CHANNEL).setMethodCallHandler(...)
   }
   

2. 验证AndroidManifest.xml配置
   确认已添加相机相关权限：

   <uses-permission android:name="android.permission.CAMERA" />
   <uses-feature android:name="android.hardware.camera" />
   <uses-feature android:name="android.hardware.camera.autofocus" />
   

3. 清除Android项目深层缓存
   进入项目的android目录，执行./gradlew clean，同时删除android/.gradle目录，再重新执行flutter pub get和flutter run。

4. 调整引擎初始化顺序
   将WidgetsFlutterBinding.ensureInitialized()放在DartPluginRegistrant.ensureInitialized()之前：

   WidgetsFlutterBinding.ensureInitialized();
   DartPluginRegistrant.ensureInitialized();
   var cameras = await availableCameras();
   

5. 升级Flutter版本
   当前使用的Flutter 3.3.6版本较旧，尝试升级到最新稳定版，修复潜在的插件兼容性问题：

   flutter upgrade
   

6. 适配低版本Android设备
   测试设备为Android 9（API 28），尝试锁定更适配该版本的camera包版本，例如0.9.4+5，并添加依赖覆盖：

   dependency_overrides:
     camera_android: 0.9.4+5
   

内容的提问来源于stack exchange，提问作者Ganessa