我是 Android 新手，我需要一条途径来满足我的要求。在我的应用程序中，我需要为用户提供一个选项来从应用程序中选择他们的播放列表。这可能吗？请确认。
我使用以下示例代码进行了尝试，在以下代码中，我尝试从 sd 卡获取文件并在列表视图中显示它们。当我尝试运行应用程序时，我强制关闭。如果我做错了什么，请您调查一下并建议我。
我的测试课。
public class TestMediaActivity extends Activity {
/** Called when the activity is first created. */
private static final String MEDIA_PATH = new String("/sdcard/");
private List<String> songs = new ArrayList<String>();
private MediaPlayer mp = new MediaPlayer();
private int currentPosition = 0;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
updateSongList();
}
public void updateSongList()
{
System.out.println("In the updateSongList");
File home = new File(MEDIA_PATH);
if (home.listFiles(new Mp3Filter()).length > 0)
{
System.out.println("\n In the condition length>0");
for (File file : home.listFiles(new Mp3Filter())) {
songs.add(file.getName());
}
setListAdapter( new ArrayAdapter<String>(this,R.layout.test_item, songs));
}
}
private void setListAdapter(ArrayAdapter<String> arrayAdapter) {
// TODO Auto-generated method stub
System.out.println("In the setListAdapter");
}
protected void onListItemClick(ListView l, View v, int position, long id)
{
currentPosition = position;
playSong(MEDIA_PATH + songs.get(position));
}
private void playSong(String songPath) {
try {
mp.reset();
mp.setDataSource(songPath);
mp.prepare();
mp.start();
// Setup listener so next song starts automatically
mp.setOnCompletionListener(new OnCompletionListener() {
public void onCompletion(MediaPlayer arg0) {
nextSong();
}
});
} catch (IOException e) {
Log.v(getString(R.string.app_name), e.getMessage());
}
}
private void nextSong() {
if (++currentPosition >= songs.size()) {
// Last song, just reset currentPosition
currentPosition = 0;
} else {
// Play next song
playSong(MEDIA_PATH + songs.get(currentPosition));
}
}
}
支持类是，
public class Mp3Filter implements FilenameFilter
{
@Override
public boolean accept(File dir, String filename) {
// TODO Auto-generated method stub
System.out.println("In the Mp3Filter");
return (filename.endsWith(".mp3"));
}
}
而日志猫中的错误是....
08-15 14:49:35.800: E/AndroidRuntime(31871): FATAL EXCEPTION: main
08-15 14:49:35.800: E/AndroidRuntime(31871): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.vsoft.TestMedia/com.vsoft.TestMedia.TestMediaActivity}: java.lang.NullPointerException
08-15 14:49:35.800: E/AndroidRuntime(31871): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2781)
08-15 14:49:35.800: E/AndroidRuntime(31871): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2797)
08-15 14:49:35.800: E/AndroidRuntime(31871): at android.app.ActivityThread.access$2300(ActivityThread.java:135)
08-15 14:49:35.800: E/AndroidRuntime(31871): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2132)
08-15 14:49:35.800: E/AndroidRuntime(31871): at android.os.Handler.dispatchMessage(Handler.java:99)
08-15 14:49:35.800: E/AndroidRuntime(31871): at android.os.Looper.loop(Looper.java:143)
08-15 14:49:35.800: E/AndroidRuntime(31871): at android.app.ActivityThread.main(ActivityThread.java:4914)
08-15 14:49:35.800: E/AndroidRuntime(31871): at java.lang.reflect.Method.invokeNative(Native Method)
08-15 14:49:35.800: E/AndroidRuntime(31871): at java.lang.reflect.Method.invoke(Method.java:521)
08-15 14:49:35.800: E/AndroidRuntime(31871): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:858)
08-15 14:49:35.800: E/AndroidRuntime(31871): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
08-15 14:49:35.800: E/AndroidRuntime(31871): at dalvik.system.NativeStart.main(Native Method)
08-15 14:49:35.800: E/AndroidRuntime(31871): Caused by: java.lang.NullPointerException
08-15 14:49:35.800: E/AndroidRuntime(31871): at com.vsoft.TestMedia.TestMediaActivity.updateSongList(TestMediaActivity.java:36)
08-15 14:49:35.800: E/AndroidRuntime(31871): at com.vsoft.TestMedia.TestMediaActivity.onCreate(TestMediaActivity.java:29)
08-15 14:49:35.800: E/AndroidRuntime(31871): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1065)
08-15 14:49:35.800: E/AndroidRuntime(31871): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2745)
08-15 14:49:35.800: E/AndroidRuntime(31871): ... 11 more