ActivityAware

如果插件需要與UI 進行互動，例如請求權限或更改Android UI ，那麼您就需要一些附加步驟來構建您的插件。您必須實現 ActivityAware，Flutter 提供了 ActivityAware 用於 Activity 的生命週期管理和獲取

public class MyPlugin implements FlutterPlugin, ActivityAware {
  //...normal plugin behavior is hidden...

  @Override
  public void onAttachedToActivity(ActivityPluginBinding activityPluginBinding) {
    // TODO: your plugin is now attached to an Activity
  }

  @Override
  public void onDetachedFromActivityForConfigChanges() {
    // TODO: the Activity your plugin was attached to was
    // destroyed to change configuration.
    // This call will be followed by onReattachedToActivityForConfigChanges().
  }

  @Override
  public void onReattachedToActivityForConfigChanges(ActivityPluginBinding activityPluginBinding) {
    // TODO: your plugin is now attached to a new Activity
    // after a configuration change.
  }

  @Override
  public void onDetachedFromActivity() {
    // TODO: your plugin is no longer associated with an Activity.
    // Clean up references.
  }
}

onAttachedToEngine和onDetachedFromEngine 是FlutterPlugin的介面方法，是flutter新的載入Plugin 的方式，onAttachedToActivity和onDetachedFromActivity是ActivityAware的介面方法，主要是用於獲取當前flutter 頁面所處的Activity.

我們可以將Plugin 設計將MethodHandler 在 onAttachedToEngine 方法中被初始化和構建，在 onDetachedFromEngine 方法中釋放；同時 Activity 相關的四個實現方法也提供了相應的操作邏輯