在原生项目中集成Flutter遇到的坑(不定期更新)

写本文章的目的在于记录在实践过程中遇到的问题，因为我发现很多文章都是一样的，当我照着其他文章的教程实践时，出现了一些问题。因此在这里记录一下：

1.在原项目中以module的方式集成flutter，在setting.gradle中添加

setBinding(new Binding([gradle: this]))
evaluate(new File(
        settingsDir.parentFile,                         
        'my_flutter/.android/include_flutter.groovy'
))

出现问题

* What went wrong:
A problem occurred evaluating settings 'xxx'.
> /Users/gindoc/Desktop/my_flutter/.android/include_flutter.groovy 
(/Users/gindoc/Desktop/my_flutter/.android/include_flutter.groovy)

你会发现你的flutter 模块名前面不是项目根目录

解决办法：

如果你创建的flutter moduel是作为原应用的子mudule，则为不需要在settingsDir后面加.parentFile，即

setBinding(new Binding([gradle: this]))
evaluate(new File(
        settingsDir,                         
        'my_flutter/.android/include_flutter.groovy'
))

2.在编写完Flutter代码后，运行报错，可以通过命令行`flutter analyze`查看错误信息。

3.由于我是在AndroidX的项目下集成flutter的，而用`flutter create -t module <module name>`方式创建的module里面的Android项目是依赖support包的，所以需要做一些修改。

方案来自https://github.com/flutter/flutter/issues/23586：
具体步骤如下
1、打开flutter module里面的.android目录下的gradle.properties，添加

android.enableJetifier=true
android.useAndroidX=true

2、将.android目录下的build.gradle的build tool版本改为3.3.1，即

buildscript {
  ...
  dependencies {
    classpath "com.android.tools.build:gradle:3.3.1"
    ...
  }
  ...
}

3、将.android目录下app里面的build.gradle的targetSdkVersion修改为28

android {
  defaultConfig {
    ...
    targetSdkVersion 28
  }
  ...
}

4、MissingPluginException(No implementation found for method getBatteryLevel on channel samples.flutter.io/battery)

在尝试在flutter中与原生交互（比如获取手机电量，跳转原生页面）时，出现MissingPluginException。
出现这种情况的原因是因为plugin没有注册成功。

这里需要注意的是: 1、每个flutterView所在的Activity都要注册plugin，否则就可能出现这种情况。 2、给activity添加flutterView的操作要在注册plugin之前

示例：

// 这里定义一个基类BaseActivity，因为
// 1、我们注册plugin需要PluginRegistry，
// 2、添加flutterView需要lifecycle或者supportFragmentManager，
// 而 FlutterActivity 和 FragmentActivity 都不能同时满足以上两个条件

abstract class BaseActivity :AppCompatActivity(), FlutterView.Provider, PluginRegistry, FlutterActivityDelegate.ViewFactory{

    private val delegate = FlutterActivityDelegate(this, this)
    private val eventDelegate: FlutterActivityEvents
    private val viewProvider: FlutterView.Provider
    private val pluginRegistry: PluginRegistry

    init {
        this.eventDelegate = this.delegate
        this.viewProvider = this.delegate
        this.pluginRegistry = this.delegate
    }


    override fun getFlutterView(): FlutterView {
        return this.viewProvider.flutterView
    }

    override fun createFlutterView(context: Context): FlutterView? {
        return null
    }

    override fun createFlutterNativeView(): FlutterNativeView? {
        return null
    }

    override fun retainFlutterNativeView(): Boolean {
        return false
    }

    override fun hasPlugin(key: String): Boolean {
        return this.pluginRegistry.hasPlugin(key)
    }

    override fun <T> valuePublishedByPlugin(pluginKey: String): T {
        return this.pluginRegistry.valuePublishedByPlugin(pluginKey)
    }

    override fun registrarFor(pluginKey: String): PluginRegistry.Registrar {
        return this.pluginRegistry.registrarFor(pluginKey)
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        this.eventDelegate.onCreate(savedInstanceState)
    }

    override fun onStart() {
        super.onStart()
        this.eventDelegate.onStart()
    }

    override fun onResume() {
        super.onResume()
        this.eventDelegate.onResume()
    }

    override fun onDestroy() {
        this.eventDelegate.onDestroy()
        super.onDestroy()
    }

    override fun onBackPressed() {
        if (!this.eventDelegate.onBackPressed()) {
            super.onBackPressed()
        }

    }

    override fun onStop() {
        this.eventDelegate.onStop()
        super.onStop()
    }

    override fun onPause() {
        super.onPause()
        this.eventDelegate.onPause()
    }

    override fun onPostResume() {
        super.onPostResume()
        this.eventDelegate.onPostResume()
    }

    override fun onRequestPermissionsResult(requestCode: Int, permissions: Array<String>, grantResults: IntArray) {
        this.eventDelegate.onRequestPermissionsResult(requestCode, permissions, grantResults)
    }

    override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
        if (!this.eventDelegate.onActivityResult(requestCode, resultCode, data)) {
            super.onActivityResult(requestCode, resultCode, data)
        }

    }

    override fun onNewIntent(intent: Intent) {
        this.eventDelegate.onNewIntent(intent)
    }

    public override fun onUserLeaveHint() {
        this.eventDelegate.onUserLeaveHint()
    }

    override fun onTrimMemory(level: Int) {
        this.eventDelegate.onTrimMemory(level)
    }

    override fun onLowMemory() {
        this.eventDelegate.onLowMemory()
    }

    override fun onConfigurationChanged(newConfig: Configuration) {
        super.onConfigurationChanged(newConfig)
        this.eventDelegate.onConfigurationChanged(newConfig)
    }
}

// FlutterView所在的Activity
class FlutterPageActivity : BaseActivity() {

    private val CHANNEL = "samples.flutter.io/battery"

    override fun onCreate(savedInstanceState: Bundle?) {
        FlutterMain.startInitialization(applicationContext)
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        // 1、创建flutterView
        val flutterView = Flutter.createView(this, lifecycle, "route1")
        val layout =
            FrameLayout.LayoutParams(FrameLayout.LayoutParams.MATCH_PARENT, FrameLayout.LayoutParams.MATCH_PARENT)
        addContentView(flutterView, layout)

        // 2、注册plugin
        GeneratedPluginRegistrant.registerWith(this)
        MethodChannel(flutterView, CHANNEL).setMethodCallHandler { call, result ->
            // 在这里和原生交互
            if (call.method == "getBatteryLevel") {
                val batteryLevel = getBatteryLevel()

                if (batteryLevel != -1) {
                    result.success(batteryLevel)
                } else {
                    result.error("UNAVAILABLE", "Battery level not available.", null)
                }
                startActivity(Intent(this@FlutterPageActivity, NativeActivity::class.java))                    // 跳转原生界面
            } else {
                result.notImplemented()
            }
        }


    }

    // 获取电量
    private fun getBatteryLevel(): Int {
        var batteryLevel = -1
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
            val batteryManager = getSystemService(Context.BATTERY_SERVICE) as BatteryManager
            batteryLevel = batteryManager.getIntProperty(BatteryManager.BATTERY_PROPERTY_CAPACITY)
        } else {
            val intent =
                ContextWrapper(applicationContext).registerReceiver(null, IntentFilter(Intent.ACTION_BATTERY_CHANGED))
            batteryLevel =
                intent!!.getIntExtra(
                    BatteryManager.EXTRA_LEVEL,
                    -1
                ) * 100 / intent.getIntExtra(BatteryManager.EXTRA_SCALE, -1)
        }

        return batteryLevel

    }

}

另外这里推荐以https://www.cnblogs.com/fuyaozhishang/p/9617234.html该博客的方式集成Android和Flutter，进行混合开发，达到原生开发和Flutter开发互不干扰。