Question

我尝试使用CursorLoader在设备上构建本地文件的音乐浏览器/播放器。我使用的是Xamarin android，c＃。我使用的是ViewPager，它位于片段内（不是FragmentActivity，因为片段是导航抽屉的一部分）。

我在使用listView.Adapter时遇到了问题，因为我无法获得该活动，因此会用于显示歌曲。在活动中直接使用此listview适配器时，它可以正常工作（我能够看到歌曲列表），但是当尝试在使用PagerAdapter的ViewPager（在片段中的所有内容）中使用它时。我无法在listView.Adapter = new SongsAdapter（ this ，cursor，songsList）中获取活动。您是否可以指导我，以便能够将活动传递给适配器或让我知道我是否做了一般的错误，这使得它无法实现？

谢谢。感谢您的帮助：）

于连

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

using Android.Support.V4.App;
using Android.Content;
using Android.OS;
using Android.Runtime;
using Android.Util;
using Android.Views;
using Android.Widget;
using Android.Support.V4.View;

using Android.Provider;
using Android.Database;
using Android.Net;


namespace project
{
    public class MyDeviceFragment : Fragment
    {
        private SlidingTabScrollView mSlidingTabScrollView;
        private ViewPager mViewPager;

        public override View OnCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
        {
            return inflater.Inflate(Resource.Layout.slidingtabfragment, container, false);
        }

        public override void OnViewCreated(View view, Bundle savedInstanceState)
        {
            var activity = Activity;
            mSlidingTabScrollView = view.FindViewById<SlidingTabScrollView>(Resource.Id.sliding_tabs);
            mViewPager = view.FindViewById<ViewPager>(Resource.Id.viewpager);
            mViewPager.Adapter = new SamplePagerAdapter();

            mSlidingTabScrollView.ViewPager = mViewPager;
        }

        public class SamplePagerAdapter : PagerAdapter
        {
            List<string> items = new List<string>();

            public SamplePagerAdapter() : base()
            {
                items.Add("PLaylists");
                items.Add("Songs");
                items.Add("Albums");
                items.Add("Artists");
                items.Add("Genres");
            }

            public override int Count
            {
                get { return items.Count; }
            }

            public override bool IsViewFromObject(View view, Java.Lang.Object obj)
            {
                return view == obj;
            }

            public override Java.Lang.Object InstantiateItem(ViewGroup container, int position)
            {
                View view = null;

                switch (position) {
                case 1:
                    ListView listView;
                    view = LayoutInflater.From (container.Context).Inflate (Resource.Layout.testinglistactivity, container, false);
                    listView = view.FindViewById<ListView> (Resource.Id.List);

                    List<Song> songsList;

                    var uri = MediaStore.Audio.Media.ExternalContentUri;
                    string[] projection = {
                        MediaStore.Audio.Media.InterfaceConsts.Id,
                        MediaStore.Audio.Media.InterfaceConsts.AlbumId,
                        MediaStore.Audio.Media.InterfaceConsts.Title,
                        MediaStore.Audio.Media.InterfaceConsts.Artist,
                    };
                    var loader = new CursorLoader (container.Context, uri, projection, null, null, null);
                    var cursor = (ICursor)loader.LoadInBackground ();
                    songsList = new List<Song> ();
                    if (cursor.MoveToFirst ()) {
                        do {
                            songsList.Add (new Song {
                                Id = cursor.GetLong (cursor.GetColumnIndex (projection [0])),
                                AlbumId = cursor.GetString (cursor.GetColumnIndex (projection [1])),
                                Title = cursor.GetString (cursor.GetColumnIndex (projection [2])),
                                Artist = cursor.GetString (cursor.GetColumnIndex (projection [3]))
                            });
                        } while (cursor.MoveToNext ());
                    }

                    listView.Adapter = new SongsAdapter (this,cursor,songsList);//***********HERE is the issue*********************
                    break;
                default:
                    view = LayoutInflater.From (container.Context).Inflate (Resource.Layout.pager_item, container, false);
                    int pos = position + 1;
                    TextView txtTitle = view.FindViewById<TextView> (Resource.Id.item_title);

                    txtTitle.Text = pos.ToString ();
                    break;
                }
                container.AddView (view);
                return view;
            }

            public string GetHeaderTitle (int position)
            {
                return items[position];
            }

            public override void DestroyItem(ViewGroup container, int position, Java.Lang.Object obj)
            {
                container.RemoveView((View)obj);
            }
        }
    }
}

Answer 1

我能够通过以下方式解决问题：

将活动作为参数传递给： mViewPager.Adapter = new MyDeviceAdapter（Activity）;

将 this.context = context添加到SamplePager适配器的构造函数

public class SamplePagerAdapter：PagerAdapter { 活动背景; 列表项=新列表（）;

    public SamplePagerAdapter(Activity context) : base()
    {
        this.context = context;
        items.Add("PLaylists");
        items.Add("Songs");
        items.Add("Albums");
        items.Add("Artists");
        items.Add("Genres");
    }

...

可选（如果需要则不是）：我将SamplePagerAdapter与另一个文件分开，我可以使用Android.App而不是Android.Support.V4.App;

Answer 2

您可以添加容器的上下文，它将解决问题：

 listView.Adapter = new SongsAdapter (container.Context,cursor,songsList);

片段中ViewPager中的Listview适配器 - 如何获取活动

2 个答案: