getParcelableArrayExtra空指针

Question

我正在使用Parcelable作为我课堂上的自定义Song对象。但是，当我试图获得一个类型为Song的arraylist时，我总是得到一个空指针异常。我没有问题从意图获取字符串额外，但当我尝试获取此ArrayList时，我需要我总是得到null。当我试图传递一个Song对象时，我也得到一个null，所以我假设它有一些问题，但是我无法弄清楚它的生命。

这是我的歌曲课程

import android.os.Parcel;
import android.os.Parcelable;
public class Song implements Parcelable {
    private String uri;
    private String title;
    private String artist;
    private String album;
    private String length;
    private int count;
    private int source;

    public Song () {

    }
    public Song (String title, String artist, String album, String uri, String length, int count,
                 int source) {
        this.uri = uri;
        this.title = title;
        this.artist = artist;
        this.album = album;
        this.length = length;
        this.count = count;
        this.source = source;
    }

    public String getUri() {
        return uri;
    }

    public String getArtist() {
        return artist;
    }

    public String getTitle() {
        return title;
    }

    public String getLength() {
        return length;
    }

    public int getCount() {return count;}
    @Override
    public String toString() {
        return title + " - " +artist;
    }

    @Override
    public boolean equals(Object o){
        if (o instanceof Song) {
            Song song = (Song) o;
            if (title.equals(song.title) && length.equals(song.length)) {
                return true;
            }
        }
        return false;
    }

    public int compareTo(Song s) {
        if (this.count < s.getCount()) {
            return -1;
        }
        else if(this.count > s.getCount()){
            return 1;
        }

        return 0;
    }


    public String getAlbum() {
        return album;
    }

    public void setAlbum(String album) {
        this.album = album;
    }

    public int getSource() {
        return source;
    }


    @Override
    public int describeContents() {
        return 0;
    }

    @Override
    public void writeToParcel(Parcel dest, int flags) {
        dest.writeString(this.uri);
        dest.writeString(this.title);
        dest.writeString(this.artist);
        dest.writeString(this.album);
        dest.writeString(this.length);
        dest.writeInt(this.count);
        dest.writeInt(this.source);
    }

    protected Song(Parcel in) {
        this.uri = in.readString();
        this.title = in.readString();
        this.artist = in.readString();
        this.album = in.readString();
        this.length = in.readString();
        this.count = in.readInt();
        this.source = in.readInt();
    }

    public static final Creator<Song> CREATOR = new Creator<Song>() {
        @Override
        public Song createFromParcel(Parcel source) {
            return new Song(source);
        }

        @Override
        public Song[] newArray(int size) {
            return new Song[size];
        }
    };
}

这是我用来封装arraylist的行

Intent intent = new Intent();
        Log.d("UTILS ", " size: " +queue.size()); // Making sure it is not null before passing
        intent.setClass(context, PlayerService.class);
        intent.putParcelableArrayListExtra(PlayerService.EXTRA_TRACK_LIST, queue);
        context.startService(intent);

这是检索PlayerService类

中的arraylist

public static final String EXTRA_TRACK_LIST = "EXTRA_TRACK_LIST";
private ArrayList<Song> trackList;
    .
    .
    .


    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {

        if (intent == null || intent.getAction() == null) {
            Log.d(TAG, "unspecified command");
            return START_STICKY;
        }

        trackList=intent.getParcelableArrayListExtra(PlayerService.EXTRA_TRACK_LIST);
        if (trackList == null) {
            Log.d("TRACKLIST", "IS NULL");
        } else {
            Log.d(TAG, "size: "+trackList.size());
        }
        .
        .
        .
        // more irrelevant code

Answer 1

您的参数错误

public static final String EXTRA_TRACK_LIST =“EXTRA_TRACK_LIST”;

这样改变

trackList = intent.getParcelableArrayListExtra(PlayerService.EXTRA_TRACK_LIST);

Answer 2

队列是队列/列表还是类似？或者它是一个数组？如果是array，应该是queue.length，对吧？从列表到数组尝试URLConnection FTP list files。这应该有用。

intent.putParcelableArrayListExtra(PlayerService.EXTRA_TRACK_LIST, queue);

如果没有，请让我知道继续尝试。此外，您还可以将其作为String传递。您可以使用GSON将其转换为JSON字符串。转换为String后，将其作为单个String传递。

Intent intent = new Intent(ActivityA.this, Service.class);
intent.putExtra(new Gson().toJson(queue), PlayerService.EXTRA_TRACK_LIST);
context.startService(intent);

再次检索该对象：

Song song = new Gson().fromJson(intent.getStringExtra(PlayerService.EXTRA_TRACK_LIST), Song.class);

或者，如果列表（我相信你的情况）：

Type listType = new TypeToken<ArrayList<Song.class>>(){}.getType();
List<Song> songList = new Gson().fromJson(intent.getStringExtra(PlayerService.EXTRA_TRACK_LIST), listType);