Question

在我试图制作parcelable的类中，有一个叫做genericSongClass的小类。在较大的类中，有一个genericSongClass的ArrayList。所以我知道我必须使genericSongClass可以使用，但是如果不使类静态，我就不能给它一个CREATOR。我有什么方法可以做到这一点吗？

我现在处于困境中的小班：

public class genericSongClass implements Parcelable {
        String songTitle = "";
        String songArtist = "";
        String songData = "";
        String songAlbum = "";
        String isChecked = "false";

        public final static Parcelable.Creator<genericSongClass> CREATOR = new Parcelable.Creator<genericSongClass>() {

            @Override
            public genericSongClass createFromParcel(Parcel source) {
                return null;
            }

            @Override
            public genericSongClass[] newArray(int size) {
                return null;
            }

        };

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

        @Override
        public void writeToParcel(Parcel dest, int flags) {             
        }
}

My Larger class（所有parcelable相关方法位于底部，使用parcel的ArrayList和构造函数位于顶部）：

public class Music implements Parcelable{

    private static ArrayList<genericSongClass> songs = null;

    Cursor cursor;

    Context context;

    public Music(Context context){
        this.context = context;
    }

    public Music(Parcel in){
        songs = in.readArrayList(songs, genericSongClass.CREATOR);
    }

    public void BindAllSongs() {        
            /** Making custom drawable */
            String selection = MediaStore.Audio.Media.IS_MUSIC + " != 0";
            final String[] projection = new String[] {
                    MediaStore.Audio.Media.DISPLAY_NAME,
                    MediaStore.Audio.Media.ARTIST,
                    MediaStore.Audio.Media.DATA,
                    MediaStore.Audio.Media.ALBUM};
                    final String sortOrder = MediaStore.Audio.AudioColumns.TITLE
                            + " COLLATE LOCALIZED ASC";

                    try {
                        // the uri of the table that we want to query
                        Uri uri = android.provider.MediaStore.Audio.Media.EXTERNAL_CONTENT_URI;
                        // query the db
                        cursor = context.getContentResolver().query(uri,
                                projection, selection, null, sortOrder);
                        if (cursor != null) {
                            songs = new ArrayList<genericSongClass>(cursor.getCount());
                            cursor.moveToFirst();                       
                            while (!cursor.isAfterLast()) { 
                                genericSongClass GSC = new genericSongClass();
                                GSC.songTitle = cursor.getString(0);
                                GSC.songArtist = cursor.getString(1);   
                                GSC.songData = cursor.getString(2);
                                GSC.songAlbum = cursor.getString(3);
                                songs.add(GSC);
                                cursor.moveToNext();
                            }
                        }
                    } catch (Exception ex) {

                    } finally {
                        if (cursor != null) {
                            cursor.close();
                        }
                    }       

        }

    public static Object[] toArray(ArrayList<Object> list){
        Object[] toReturn = new Object[list.size()];
        for (int i = 0; i < list.size(); i++){
            toReturn[i] = list.get(i);
        }
        return toReturn;
    }

    public ArrayList<String> getArtists(){
        ArrayList<String> artists = new ArrayList<String>();
        for(genericSongClass gsc: songs){
            if(!artists.contains(gsc.songArtist)){
                artists.add(gsc.songArtist);
            }
        }
        Alphabetize forArtists = new Alphabetize(artists);
        return forArtists.getSortedArrayList();
    }

    public ArrayList<String> getAlbums(String artist){
        ArrayList<String> albums = new ArrayList<String>();
        for(genericSongClass gsc: songs){
            if(gsc.songArtist == artist){
                albums.add(gsc.songAlbum);
            }
        }
        Alphabetize forAlbums = new Alphabetize(albums);
        return forAlbums.getSortedArrayList();
    }

    //--- Parcel ------------------------------------------------

     public static final Parcelable.Creator<Music> CREATOR = new Parcelable.Creator<Music>() {  

            public Music createFromParcel(Parcel in) {  
                return new Music(in);  
            }

            @Override
            public Music[] newArray(int size) {
                return null;
            }  
        };

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

    @Override
    public void writeToParcel(Parcel dest, int flags) {
        dest.writeList(songs);
    }



}

这是我第一次尝试使用Parcelable，欢迎任何帮助！提前谢谢！

Answer 1

首先关闭：考虑遵循Java惯例并将genericSongClass重命名为GenericSong。其余部分假设您没有更改该名称。

第二关：在使用/了解Parcelables时阅读这本惊人的指南 http://blog.logicexception.com/2012/09/a-parcelable-tutorial-for-android.html

最后：您确切代码的部分或全部解决方案：

在genericSongClass中添加新的构造函数：

public genericSongClass(Parcel in) {
    songTitle = in.readString();
    // read in the rest of your values here
}

并添加默认构造函数：

public genericSongClass() {
}

CREATOR中的genericSongClass应如下所示：（同时调整Music类

public final static Parcelable.Creator<genericSongClass> CREATOR = new Parcelable.Creator<genericSongClass>() {

    @Override
    public genericSongClass createFromParcel(Parcel source) {
        return new genericSongClass(source);
    }

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

};

调整writeToParcel方法：

@Override
public void writeToParcel(Parcel dest, int flags) {   
    dest.writeString(songTitle);
    // write your other values here
}

保持秩序，这是重要的！读取和写入的顺序应该相同！

在Music类构造函数中：

in.readTypedList(songs, genericSongClass.CREATOR);

在Music班writeToParcel：

dest.writeTypedList(songs);

Android：如何创建一个实现Parcelable的类，该类包含非静态自定义类的ArrayList

1 个答案: