您好我还在尝试制作我的wavPlayer。我的应用程序包含包含wav文件的listitem。当我点击一个文件时，它应该被播放，但它没有。我已经在OnListItemClick（）上尝试了一些方法使它工作（我用双斜杠标记它），但它仍然是错误的。大多数错误都是nullpointer。有人可以帮帮我吗？
这是我的代码和日志猫
public class PlayercobaActivity extends ListActivity implements View.OnClickListener {
private MediaCursorAdapter mediaAdapter = null;
PlayAudio playTask;
Button startRecordingButton, stopRecordingButton, startPlaybackButton,
stopPlaybackButton;
boolean isPlaying = false;
int frequency = 11025;
int channelConfiguration = AudioFormat.CHANNEL_CONFIGURATION_MONO;
int audioEncoding = AudioFormat.ENCODING_PCM_16BIT;
//File item ;
String item;
// File path = new File(Environment.getExternalStorageDirectory().getAbsolutePath() + "/Datarekaman/recording5.wav");
//Cursor acursor;
Cursor cursor;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_playercoba);
startPlaybackButton = (Button) this .findViewById(R.id.StartPlaybackButton);
stopPlaybackButton = (Button) this.findViewById(R.id.StopPlaybackButton);
startPlaybackButton.setOnClickListener(this);
stopPlaybackButton.setOnClickListener(this);
startPlaybackButton.setEnabled(true);
stopPlaybackButton.setEnabled(false);
ContentResolver cr = getContentResolver();
Uri uri = MediaStore.Files.getContentUri("external");
String[] projection = null;
String sortOrder = null; // unordered
String selectionMimeType = MediaStore.Files.FileColumns.MIME_TYPE + "=?";
String mimeType = MimeTypeMap.getSingleton().getMimeTypeFromExtension("wav");
String[] selectionArgsPdf = new String[]{ mimeType };
Cursor cursor = cr.query(uri, projection , selectionMimeType, selectionArgsPdf, sortOrder );
if(null != cursor)
{
cursor.moveToFirst();
mediaAdapter = new MediaCursorAdapter(this, R.layout.listitem, cursor);
setListAdapter(mediaAdapter);
}
}
//@Override
public void onListItemClick(ListView list, View view, int position, long id) {
super.onListItemClick(list, view, position, id);
//String name = cursor.getString(cursor. getColumnIndex(MediaStore. MediaColumns.DISPLAY_NAME));
//item =(String) list.getItemAtPosition(position);
//File item = new File(name);
//item = new File();
//item = (String) view.getTag();
//item = (String) getListAdapter().getItem(position);
item = cursor.getString(cursor. getColumnIndex(MediaStore. MediaColumns.DATA));
//playTask = new PlayAudio();
//playTask.execute();
Toast.makeText(this, item + " selected", Toast.LENGTH_LONG).show();
}
public void onClick(View v) {
if (v == startPlaybackButton) {
play();
} else if (v == stopPlaybackButton) {
stopPlaying();
}
}
public void play() {
startPlaybackButton.setEnabled(false);
playTask = new PlayAudio();
playTask.execute();
stopPlaybackButton.setEnabled(true);
}
public void stopPlaying() {
isPlaying = false;
stopPlaybackButton.setEnabled(false);
startPlaybackButton.setEnabled(true);
}
private class PlayAudio extends AsyncTask<Void, Integer, Void> {
@Override
protected Void doInBackground(Void... params) {
isPlaying = true;
int bufferSize = AudioTrack.getMinBufferSize(frequency,
channelConfiguration, audioEncoding);
short[] audiodata = new short[bufferSize/4];
try {
DataInputStream dis = new DataInputStream(
new BufferedInputStream(new FileInputStream(item)));
AudioTrack audioTrack = new AudioTrack(
AudioManager.STREAM_MUSIC, frequency,
channelConfiguration, audioEncoding, bufferSize,
AudioTrack.MODE_STREAM);
audioTrack.play();
while (isPlaying && dis.available() > 0) {
int i = 0;
while (dis.available() > 0 && i < audiodata.length) {
audiodata[i] = dis.readShort();
i++;
}
audioTrack.write(audiodata, 0, audiodata.length);
}
dis.close();
startPlaybackButton.setEnabled(false);
stopPlaybackButton.setEnabled(true);
} catch (Throwable t) {
Log.e("AudioTrack", "Playback Failed");
}
return null;
}
protected void onPostExecute(Void result) {
startPlaybackButton.setEnabled(true);
stopPlaybackButton.setEnabled(false);
}
}
private class MediaCursorAdapter extends SimpleCursorAdapter {
public MediaCursorAdapter(Context context, int layout, Cursor c) {
super(context, layout, c,
new String[] { MediaStore.MediaColumns.DISPLAY_NAME},
new int[] { R.id.displayname});
}
}
}
logcat的
05-19 23:01:17.015 13752-13752/com.example.agita.playercoba E/AndroidRuntime﹕ FATAL EXCEPTION: main
java.lang.NullPointerException
at com.example.agita.playercoba.PlayercobaActivity.onListItemClick(PlayercobaActivity.java:93)
at android.app.ListActivity$2.onItemClick(ListActivity.java:319)
at android.widget.AdapterView.performItemClick(AdapterView.java:301)
at android.widget.AbsListView.performItemClick(AbsListView.java:1287)
at android.widget.AbsListView$PerformClick.run(AbsListView.java:3078)
at android.widget.AbsListView$1.run(AbsListView.java:4159)
at android.os.Handler.handleCallback(Handler.java:615)
at android.os.Handler.dispatchMessage(Handler.java:92)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4947)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1038)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:805)
at dalvik.system.NativeStart.main(Native Method)
答案 0 :(得分：0)
如果你正在扩展CursorAdapter，你可以通过onListItemClick
Cursor cursor = (Cursor) list.getItemAtPosition(position);
item = cursor.getString(cursor. getColumnIndex(MediaStore. MediaColumns.DATA));
Toast.makeText(this, item + " selected", Toast.LENGTH_LONG).show();