Xamarin Android中已弃用CursorLoader的替代方案及日历列表获取方法

问题背景 #

开发Xamarin Android应用时，需要获取系统日历列表，但现有实现使用了已废弃的CursorLoader，需要替代方案。原代码如下：

AndroidCalendarModels _androidCalendarModel = new AndroidCalendarModels();
string[] calendarsProjection = {
    CalendarContract.Calendars.InterfaceConsts.Id,
    CalendarContract.Calendars.InterfaceConsts.CalendarDisplayName,
    CalendarContract.Calendars.InterfaceConsts.AccountName 
};

var calendarsUri = CalendarContract.Calendars.ContentUri;            
var loader = new CursorLoader(Android.App.Application.Context, calendarsUri, calendarsProjection, null, null, null);
var cursor = (ICursor)loader.LoadInBackground();

while (cursor.MoveToNext())
{
    int calId = cursor.GetInt(0);
    string calName = cursor.GetString(1);
    string calAccount = cursor.GetString(2);

    _androidCalendarModel.Calendars.Add(new AndroidCalendarModel()
    {
        Id = calId,
        AccountName = calAccount,
        CalendarDisplayName = calName,
    });
}

替代实现方案 #

直接使用ContentResolver的Query方法即可替代CursorLoader，这是官方推荐的替代方式，无需依赖已废弃的Loader类。

1. 修改后的核心代码

AndroidCalendarModels _androidCalendarModel = new AndroidCalendarModels();
string[] calendarsProjection = {
    CalendarContract.Calendars.InterfaceConsts.Id,
    CalendarContract.Calendars.InterfaceConsts.CalendarDisplayName,
    CalendarContract.Calendars.InterfaceConsts.AccountName 
};

var calendarsUri = CalendarContract.Calendars.ContentUri;
// 使用ContentResolver.Query替代CursorLoader
using (var cursor = Application.Context.ContentResolver.Query(calendarsUri, calendarsProjection, null, null, null))
{
    if (cursor != null)
    {
        while (cursor.MoveToNext())
        {
            int calId = cursor.GetInt(cursor.GetColumnIndex(CalendarContract.Calendars.InterfaceConsts.Id));
            string calName = cursor.GetString(cursor.GetColumnIndex(CalendarContract.Calendars.InterfaceConsts.CalendarDisplayName));
            string calAccount = cursor.GetString(cursor.GetColumnIndex(CalendarContract.Calendars.InterfaceConsts.AccountName));

            _androidCalendarModel.Calendars.Add(new AndroidCalendarModel()
            {
                Id = calId,
                AccountName = calAccount,
                CalendarDisplayName = calName,
            });
        }
    }
}

2. 关键注意事项

• 权限申请：必须在AndroidManifest.xml中添加日历读取权限，同时在运行时动态申请：

  <uses-permission android:name="android.permission.READ_CALENDAR" />
  

  动态权限申请代码示例：

  if (ContextCompat.CheckSelfPermission(this, Manifest.Permission.ReadCalendar) != Permission.Granted)
  {
      ActivityCompat.RequestPermissions(this, new string[] { Manifest.Permission.ReadCalendar }, 100);
  }
  

• Android 11+适配：针对Android 11及以上版本，需要在Manifest中添加查询权限声明，确保能正常访问日历数据：

  <queries>
      <intent>
          <action android:name="android.content.action.VIEW" />
          <data android:mimeType="vnd.android.cursor.dir/event" />
      </intent>
  </queries>
  

• Cursor资源管理：使用using语句包裹Cursor，确保资源自动释放，避免内存泄漏。

内容的提问来源于stack exchange，提问作者Libor Foltynek