类型不匹配：推断的类型为MainActivity，但预期为FlutterEngine

问题描述

我是扑朔迷离的新手，我想更改设备的墙纸，但需要从平台通道调用方法 https://developer.android.com/reference/android/Manifest.permission?hl=en#SET_WALLPAPER 和 native android wallpaperManager

在android文件夹/MainActivity.kt Kotlin文件下会引发错误。

我在下面尝试过这些：

• 带有MainActivity.java文件的新项目
• 干净整洁
• flutter pub缓存修复

我从这里了解到其他类型的不匹配错误问题，但不幸的是没有找到任何内容。

任何需要帮助的人。 我的代码如下。

MainActivity.kt

    package com.combasis.wallpaper_son_app
import android.os.Bundle
import io.flutter.app.FlutterActivity
import io.flutter.plugin.common.MethodChannel
import io.flutter.plugins.GeneratedPluginRegistrant
import java.io.IOException
import android.app.WallpaperManager
import android.graphics.BitmapFactory
import java.io.File
import android.os.Build
import android.annotation.TargetApi
import android.content.Context
import io.flutter.Log

private const val CHANNEL = "com.combasis.wallpaper_son_app"
class MainActivity: FlutterActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        GeneratedPluginRegistrant.registerWith(this)

    MethodChannel(flutterView,CHANNEL).setMethodCallHandler { call,result ->
        if (call.method == "setWallpaper") {
            val arguments = call.arguments as ArrayList<*>
            val setWallpaper = setWallpaper(arguments[0] as String,applicationContext,arguments[1] as Int)

            if (setWallpaper == 0) {
                result.success(setWallpaper)
            } else {
                result.error("UNAVAILABLE","",null)
            }
        } else {
            result.notImplemented()
        }
    }
}

@TargetApi(Build.VERSION_CODES.ECLAIR)
private fun setWallpaper(path: String,applicationContext: Context,wallpaperType: Int): Int {
    var setWallpaper = 1
    val bitmap = BitmapFactory.decodeFile(path)
    val wm: WallpaperManager? = WallpaperManager.getInstance(applicationContext)
    setWallpaper = try {
        wm?.setBitmap(bitmap,null,true,wallpaperType)
        0
    } catch (e: IOException) {
        1
    }

    return setWallpaper
}
}

main.dart：...

  static const platform = const MethodChannel('com.combasis.wallpaper_son_app');
  Future<void> _setWallpaper(int wallpaperType,String url) async {
    var file =
    await DefaultCacheManager().getSingleFile(url);
    try {
      final int result = await platform
          .invokeMethod('setWallpaper',[file.path,wallpaperType]);
      print('Wallpaper Updated.... $result');
    } on PlatformException catch (e) {
      print("Failed to Set Wallpaper: '${e.message}'.");
    }
  }

运行：

 Launching lib/main.dart on AOSP on IA Emulator in debug mode...
Running Gradle task 'assembleDebug'...
e: /Users/username/AndroidStudioProjects/walpaperz_app/wallpaper_son_app/android/app/src/main/kotlin/com/combasis/wallpaper_son_app/MainActivity.kt: (21,48): Type mismatch: inferred type is MainActivity but FlutterEngine was expected

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':app:compileDebugKotlin'.
> Compilation error. See log for more details

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.

* Get more help at https://help.gradle.org

BUILD FAILED in 13s
Exception: Gradle task assembleDebug failed with exit code 1

-Android Studio版本：4.0.1

-kotlin版本：1.3.72-release-Studio4.0-5稳定

-Flutter版本：1.17.2稳定

解决方法

请从 GeneratedPluginRegistrant.registerWith(flutterEngine); 中删除 MainActivity.kt 并更新如下。

import io.flutter.embedding.android.FlutterActivity

class MainActivity: FlutterActivity() {
}

,

要传递颤振引擎值，我们可以使用 provideFlutterEngine 方法。对于 flutterView，我们可以使用 flutterEngine.dartExecutor。下面是代码片段。

class MainActivity: FlutterActivity() {
private val CHANNEL = "com.startActivity/testChannel"
override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    provideFlutterEngine(this)?.let { GeneratedPluginRegistrant.registerWith(it) }
    MethodChannel(flutterEngine?.dartExecutor,CHANNEL).setMethodCallHandler{ call,result ->
        if(call.method.equals("StartSecondActivity")){
            val intent= Intent(this,KotlinActivity::class.java)
            startActivity(intent)
            result.success("ActivityStarted")
        }
        else{
            result.notImplemented()
        }
    }
}}

,

您可以使用flutter create或通过IDE向导来创建新应用，MainActivity.kt可能如下：

class MainActivity: FlutterActivity() {
    override fun configureFlutterEngine(@NonNull flutterEngine: FlutterEngine) {
        GeneratedPluginRegistrant.registerWith(flutterEngine);
    }
}

然后从中开始工作。