Question

我正在尝试为Android操作系统构建音乐播放器。我正在动态创建一个listView，并使用Uri设置标签，以便稍后可以使用getTag对Uris进行检索。但是，这不起作用。它在getTag行给出了ClassCastException。这是我的代码：

SongList.java：

    import android.content.ContentResolver;
    import android.database.Cursor;
    import android.media.MediaPlayer;
    import android.net.Uri;
    import android.os.Bundle;
    import android.support.v4.app.Fragment;
    import android.view.LayoutInflater;
    import android.view.View;
    import android.view.ViewGroup;
    import android.widget.AdapterView;
    import android.widget.ListView;
    import android.widget.Toast;

    import java.util.ArrayList;
    import java.util.Collections;
    import java.util.Comparator;

    public class SongList extends Fragment {

        private ArrayList<Song> songList;

        public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
            View view = inflater.inflate(R.layout.fragment_song_list, container, false);

            //retrieve list view
            ListView songView = (ListView)view.findViewById(R.id.listView);

            //instantiate list
            songList = new ArrayList<>();

            getSongList();

            Collections.sort(songList, new Comparator<Song>() {
                public int compare(Song a, Song b) {
                    return a.getTitle().compareTo(b.getTitle());
                }
            });

            final SongAdapter songAdapter = new SongAdapter( getActivity(), songList);
            songView.setAdapter(songAdapter);

            songView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
                @Override
                public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                    setSong(view);
                }
            });

            return view;
        }

        void getSongList() {
            //retrieve song info
            ContentResolver musicResolver = getActivity().getContentResolver();
            Uri musicUri = android.provider.MediaStore.Audio.Media.EXTERNAL_CONTENT_URI;
            Cursor musicCursor = musicResolver.query(musicUri, null, null, null, null);

            //iterate through music
            if(musicCursor!=null && musicCursor.moveToFirst()){
                //get columns
                int idColumn                = musicCursor.getColumnIndex(android.provider.MediaStore.Audio.Media._ID);
                int titleColumn             = musicCursor.getColumnIndex(android.provider.MediaStore.Audio.Media.TITLE);
                int artistColumn            = musicCursor.getColumnIndex(android.provider.MediaStore.Audio.Media.ARTIST);
                int albumColumn             = musicCursor.getColumnIndex(android.provider.MediaStore.Audio.Media.ALBUM);
                int albumIdColumn           = musicCursor.getColumnIndex(android.provider.MediaStore.Audio.Media.ALBUM_ID);
                int UriColumn               = musicCursor.getColumnIndex(android.provider.MediaStore.Audio.Media.DATA);
                //add songs to list
                do {
                    long thisId         = musicCursor.getLong(idColumn);
                    String thisTitle    = musicCursor.getString(titleColumn);
                    String thisArtist   = musicCursor.getString(artistColumn);
                    String thisAlbum    = musicCursor.getString(albumColumn);
                    long thisAlbumId    = musicCursor.getLong(albumIdColumn);
                    Uri thisUri         = Uri.parse( musicCursor.getString( UriColumn ) );

                    songList.add(new Song(thisId, thisTitle, thisArtist, thisAlbum, thisAlbumId, thisUri));
                }
                while (musicCursor.moveToNext());
            }
        }

        public void setSong(View view) {
            if ( MainActivity.isCreatedCheck() ){
                Toast.makeText(getActivity(), "Already started", Toast.LENGTH_LONG).show();
            }else {
                Uri songUri = (Uri) view.getTag();
                final MediaPlayer mediaPlayer = MediaPlayer.create(getActivity(), songUri);
                mediaPlayer.setOnPreparedListener(new MediaPlayer.OnPreparedListener() {
                    @Override
                    public void onPrepared(MediaPlayer mp) {
                        mediaPlayer.start();
                    }
                });
            }
        }
    }

SongAdapter.java:


import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.RelativeLayout;
import android.widget.TextView;

import java.util.ArrayList;

public class SongAdapter extends BaseAdapter {

    //song list and layout
    private ArrayList<Song> songs;
    private LayoutInflater songInf;

    //constructor
    public SongAdapter(Context c, ArrayList<Song> theSongs){
        songs=theSongs;
        songInf=LayoutInflater.from(c);
    }

    @Override
    public int getCount() {
        return songs.size();
    }

    @Override
    public Object getItem(int arg0) {
        return null;
    }

    @Override
    public long getItemId(int arg0) {
        return 0;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {

        //map to song layout
        RelativeLayout songLay = (RelativeLayout) songInf.inflate(R.layout.song_list_item, parent, false);

        //get title and artist views
        TextView songView               = (TextView)songLay.findViewById(R.id.titleListTextView);
        TextView artistView             = (TextView)songLay.findViewById(R.id.artistListTextView);
        RelativeLayout relativeLayout   = (RelativeLayout)songLay.findViewById(R.id.layoutSelector);

        //get song using position
        Song currSong = songs.get(position);

        //get title and artist strings
        songView.setText(currSong.getTitle());
        artistView.setText(currSong.getArtist());

        relativeLayout.setTag( currSong.getURI() );

        //set position as tag
        songLay.setTag(position);
        return songLay;
    }

}

song_list_item.xml：

<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:background="@color/gray_200"
    android:layout_marginBottom="@dimen/bottom_song_border"
    android:layout_height="@dimen/song_height"
    android:id="@+id/layoutSelector">

        <com.makeramen.RoundedImageView
            xmlns:app="http://schemas.android.com/apk/res-auto"
            android:src="@drawable/album_default"
            android:id="@+id/albumListImageView"
            android:layout_width="@dimen/song_album_metrics"
            android:layout_height="@dimen/song_album_metrics"
            app:riv_corner_radius="30dip"
            app:riv_oval="true"
            android:layout_centerVertical="true"
            android:layout_marginStart="@dimen/song_image_margin"/>

        <TextView
            android:singleLine="true"
            android:ellipsize="end"
            android:layout_width="fill_parent"
            android:textSize="@dimen/song_title_text_size"
            android:id="@+id/titleListTextView"
            android:layout_height="wrap_content"
            android:text="@string/song_title"
            android:layout_marginStart="@dimen/song_title_margin"
            android:layout_centerVertical="true"
            android:paddingBottom="16dp"/>

        <TextView
            android:singleLine="true"
            android:ellipsize="end"
            android:layout_width="wrap_content"
            android:id="@+id/artistListTextView"
            android:layout_height="wrap_content"
            android:text="@string/song_artist"
            android:textSize="@dimen/song_artist_text_size"
            android:layout_marginStart="@dimen/song_title_margin"
            android:layout_centerVertical="true"
            android:paddingTop="20dp"/>

</RelativeLayout>

如果有人可以帮助我，那就太棒了。

Answer 1

您要将标记设置为同一视图两次;首先是Uri，然后是整数。由于此设置Uri，因为标记被整数覆盖，从而产生ClassCastException。如果仔细查看，则songLay和relativeLayout代表相同的观点。

删除以下行，它会起作用。

songLay.setTag(position);

无法使用getTag获取Uri

1 个答案: