Activity Action: Display the event to the user in the custom app as specified in NoType:android/provider/CalendarContract$EventsColumns;Href=../../../reference/android/provider/CalendarContract.EventsColumns.html#CUSTOM_APP_PACKAGE. The custom app will be started via Android.App.Activity.StartActivityForResult(Android.Content.Intent, System.Int32) and it should call Android.App.Activity.SetResult(Android.App.Result) with Android.App.Activity.RESULT_OK or Android.App.Activity.RESULT_CANCELED to acknowledge whether the action was handled or not. The custom app should have an intent filter like the following:

 <intent-filter>
    <action android:name="android.provider.calendar.action.HANDLE_CUSTOM_EVENT" />
    <category android:name="android.intent.category.DEFAULT" />
    <data android:mimeType="vnd.android.cursor.item/event" />
 </intent-filter>

Input: Android.Content.Intent.Data has the event URI. The extra CalendarContract.ExtraEventBeginTime has the start time of the instance. The extra CalendarContract.ExtraCustomAppUri will have the NoType:android/provider/CalendarContract$EventsColumns;Href=../../../reference/android/provider/CalendarContract.EventsColumns.html#CUSTOM_APP_URI.

Output: Android.App.Activity.RESULT_OK if this was handled; otherwise Android.App.Activity.RESULT_CANCELED.

[Android Documentation]