将 Android 列表视图连接到另一个活动

Question

我正在制作一个MP3播放器Android应用程序。我想从 ListView 单击开始另一个活动，该单击打开艺术家目录以显示该艺术家的歌曲。我的代码基于[Android教程][1]。

以下是我的在艺术家列表中创建.java

    ListView lv = getListView();
    lv.setOnItemClickListener(new OnItemClickListener() {
        public void onItemClick(AdapterView<?> parent, View v,int position, long id) {
            Intent intent = new Intent(getApplicationContext(), SongList.class);
            String artistSongPath = artistsList.get(position).get("artistPath");//gets artist SDcard path
            System.out.println("artistSongPath = " + artistSongPath); //prints out correct path
            intent.putExtra("A_S_PATH", artistSongPath); //puts the artistSongPath static A_S_Path
            startActivity(intent); //start the intent
        }
    });

在我的艺术家列表的顶部.java我有

    public final static String A_S_PATH = "wecode.mp3playerapp.MESSAGE";

在我的歌单中.java

 @Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.song_list);
    Intent intent = getIntent();
    String path = intent.getStringExtra(ArtistList.A_S_PATH) + "/";
    System.out.println(path);
    try {
        File fp = new File(path);
        findArtistSongs(fp);
    }catch(NullPointerException npe){
        System.out.println("Could not find path.");
    }
}

A_S_Path是空的，我没有进入我的捕获。请帮忙！这是我的第一个应用程序！！

Answer 1

更改此设置

    @Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.song_list);
    Intent intent = getIntent();
    String path = intent.getStringExtra("A_S_PATH") + "/"; //here is the line that I changed
    System.out.println(path);
    try {
        File fp = new File(path);
        findArtistSongs(fp);
    }catch(NullPointerException npe){
        System.out.println("Could not find path.");
    }

Answer 2

在您的艺术家列表中.java您有：

intent.putExtra("A_S_PATH", artistSongPath);

但是在SongList.java中，你有：

String path = intent.getStringExtra(ArtistList.A_S_PATH) + "/";

您是否注意到"A_S_PATH"与您定义的ArtistList.A_S_PATH不同？