我正在Android Studio中开发音乐播放器应用程序。
这是我的SongsManager.java
package com.example.mudit.take6;
/**
* Created by Mudit on 16/04/16.
*/
import java.io.File;
import java.io.FilenameFilter;
import java.util.ArrayList;
import java.util.HashMap;
public class SongsManager {
// SDCard Path
final String MEDIA_PATH = new String("/sdcard/");
private ArrayList<HashMap<String, String>> songsList = new ArrayList<HashMap<String, String>>();
// Constructor
public SongsManager(){
}
/**
* Function to read all mp3 files from sdcard
* and store the details in ArrayList
* */
public ArrayList<HashMap<String, String>> getPlayList() {
File home = new File(MEDIA_PATH);
if (home.listFiles(new FileExtensionFilter()).length > 0) {
for (File file : home.listFiles(new FileExtensionFilter())) {
HashMap<String, String> song = new HashMap<String, String>();
song.put("songTitle", file.getName().substring(0, (file.getName().length() - 4)));
song.put("songPath", file.getPath());
// Adding each song to SongList
songsList.add(song);
}
}
// return songs list array
return songsList;
}
/**
* Class to filter files which are having .mp3 extension
* */
class FileExtensionFilter implements FilenameFilter {
public boolean accept(File dir, String name) {
return (name.endsWith(".mp3") || name.endsWith(".MP3"));
}
}
}
这是我的AndroidBuildingMusicPlayerActivity.java
package com.example.mudit.take6;
/**
* Created by Mudit on 16/04/16.
*/
import android.app.Activity;
import android.content.Intent;
import android.media.MediaPlayer;
import android.media.MediaPlayer.OnCompletionListener;
import android.os.Bundle;
import android.os.Handler;
import android.view.View;
import android.widget.Button;
import android.widget.SeekBar;
import android.widget.TextView;
import android.widget.Toast;
import java.io.IOException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Random;
public class AndroidBuildingMusicPlayerActivity extends Activity implements OnCompletionListener, SeekBar.OnSeekBarChangeListener {
private Button btnPlay;
private Button btnForward;
private Button btnBackward;
private Button btnNext;
private Button btnPrevious;
private Button btnPlaylist;
private Button btnRepeat;
private Button btnShuffle;
private SeekBar songProgressBar;
private TextView songTitleLabel;
private TextView songCurrentDurationLabel;
private TextView songTotalDurationLabel;
// Media Player
private MediaPlayer mp;
// Handler to update UI timer, progress bar etc,.
private Handler mHandler = new Handler();;
private SongsManager songManager;
private Utilities utils;
private int seekForwardTime = 5000; // 5000 milliseconds
private int seekBackwardTime = 5000; // 5000 milliseconds
private int currentSongIndex = 0;
private boolean isShuffle = false;
private boolean isRepeat = false;
private ArrayList<HashMap<String, String>> songsList = new ArrayList<HashMap<String, String>>();
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_player);
// All player buttons
btnPlay = (Button) findViewById(R.id.btplay);
// btnForward = (ImageButton) findViewById(R.id.bt);
//btnBackward = (ImageButton) findViewById(R.id.btnBackward);
btnNext = (Button) findViewById(R.id.btnxt);
btnPrevious = (Button) findViewById(R.id.btprv);
//btnPlaylist = (ImageButton) findViewById(R.id.btnPlaylist);
btnRepeat = (Button) findViewById(R.id.btrep);
btnShuffle = (Button) findViewById(R.id.btsh);
//songProgressBar = (SeekBar) findViewById(R.id.songProgressBar);
//songTitleLabel = (TextView) findViewById(R.id.songTitle);
//songCurrentDurationLabel = (TextView) findViewById(R.id.songCurrentDurationLabel);
//songTotalDurationLabel = (TextView) findViewById(R.id.songTotalDurationLabel);
// Mediaplayer
mp = new MediaPlayer();
songManager = new SongsManager();
utils = new Utilities();
// Listeners
if (songProgressBar != null) {
songProgressBar.setOnSeekBarChangeListener(this);} // Important
mp.setOnCompletionListener(this); // Important
// Getting all songs list
songsList = songManager.getPlayList();
// By default play first song
playSong(0);
/**
* Play button click event
* plays a song and changes button to pause image
* pauses a song and changes button to play image
* */
btnPlay.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View arg0) {
// check for already playing
if(mp.isPlaying()){
if(mp!=null){
mp.pause();
// Changing button image to play button
// btnPlay.setImageResource(R.drawable.play);
}
}else{
// Resume song
if(mp!=null){
mp.start();
// Changing button image to pause button
// btnPlay.setImageResource(R.drawable.pause);
}
}
}
});
/**
* Forward button click event
* Forwards song specified seconds
* */
btnForward.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View arg0) {
// get current song position
int currentPosition = mp.getCurrentPosition();
// check if seekForward time is lesser than song duration
if(currentPosition + seekForwardTime <= mp.getDuration()){
// forward song
mp.seekTo(currentPosition + seekForwardTime);
}else{
// forward to end position
mp.seekTo(mp.getDuration());
}
}
});
/**
* Backward button click event
* Backward song to specified seconds
* */
btnBackward.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View arg0) {
// get current song position
int currentPosition = mp.getCurrentPosition();
// check if seekBackward time is greater than 0 sec
if(currentPosition - seekBackwardTime >= 0){
// forward song
mp.seekTo(currentPosition - seekBackwardTime);
}else{
// backward to starting position
mp.seekTo(0);
}
}
});
/**
* Next button click event
* Plays next song by taking currentSongIndex + 1
* */
btnNext.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View arg0) {
// check if next song is there or not
if(currentSongIndex < (songsList.size() - 1)){
playSong(currentSongIndex + 1);
currentSongIndex = currentSongIndex + 1;
}else{
// play first song
playSong(0);
currentSongIndex = 0;
}
}
});
/**
* Back button click event
* Plays previous song by currentSongIndex - 1
* */
btnPrevious.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View arg0) {
if(currentSongIndex > 0){
playSong(currentSongIndex - 1);
currentSongIndex = currentSongIndex - 1;
}else{
// play last song
playSong(songsList.size() - 1);
currentSongIndex = songsList.size() - 1;
}
}
});
/**
* Button Click event for Repeat button
* Enables repeat flag to true
* */
btnRepeat.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View arg0) {
if(isRepeat){
isRepeat = false;
Toast.makeText(getApplicationContext(), "Repeat is OFF", Toast.LENGTH_SHORT).show();
// btnRepeat.setImageResource(R.drawable.repeat);
}else{
// make repeat to true
isRepeat = true;
Toast.makeText(getApplicationContext(), "Repeat is ON", Toast.LENGTH_SHORT).show();
// make shuffle to false
isShuffle = false;
//btnRepeat.setImageResource(R.drawable.btn_repeat_focused);
// btnShuffle.setImageResource(R.drawable.btn_shuffle);
}
}
});
/**
* Button Click event for Shuffle button
* Enables shuffle flag to true
* */
btnShuffle.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View arg0) {
if(isShuffle){
isShuffle = false;
Toast.makeText(getApplicationContext(), "Shuffle is OFF", Toast.LENGTH_SHORT).show();
// btnShuffle.setImageResource(R.drawable.btn_shuffle);
}else{
// make repeat to true
isShuffle= true;
Toast.makeText(getApplicationContext(), "Shuffle is ON", Toast.LENGTH_SHORT).show();
// make shuffle to false
isRepeat = false;
// btnShuffle.setImageResource(R.drawable.btn_shuffle_focused);
// btnRepeat.setImageResource(R.drawable.btn_repeat);
}
}
});
/**
* Button Click event for Play list click event
* Launches list activity which displays list of songs
* */
btnPlaylist.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View arg0) {
Intent i = new Intent(getApplicationContext(), PlayListActivity.class);
startActivityForResult(i, 100);
}
});
}
/**
* Receiving song index from playlist view
* and play the song
* */
@Override
protected void onActivityResult(int requestCode,
int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
if(resultCode == 100){
currentSongIndex = data.getExtras().getInt("songIndex");
// play selected song
playSong(currentSongIndex);
}
}
/**
* Function to play a song
* @param songIndex - index of song
* */
public void playSong(int songIndex){
// Play song
try {
mp.reset();
mp.setDataSource(songsList.get(songIndex).get("songPath"));
mp.prepare();
mp.start();
// Displaying Song title
String songTitle = songsList.get(songIndex).get("songTitle");
songTitleLabel.setText(songTitle);
// Changing Button Image to pause image
// btnPlay.setImageResource(R.drawable.pause);
// set Progress bar values
songProgressBar.setProgress(0);
songProgressBar.setMax(100);
// Updating progress bar
updateProgressBar();
} catch (IllegalArgumentException e) {
e.printStackTrace();
} catch (IllegalStateException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
/**
* Update timer on seekbar
* */
public void updateProgressBar() {
mHandler.postDelayed(mUpdateTimeTask, 100);
}
/**
* Background Runnable thread
* */
private Runnable mUpdateTimeTask = new Runnable() {
public void run() {
long totalDuration = mp.getDuration();
long currentDuration = mp.getCurrentPosition();
// Displaying Total Duration time
songTotalDurationLabel.setText(""+utils.milliSecondsToTimer(totalDuration));
// Displaying time completed playing
songCurrentDurationLabel.setText(""+utils.milliSecondsToTimer(currentDuration));
// Updating progress bar
int progress = (int)(utils.getProgressPercentage(currentDuration, totalDuration));
//Log.d("Progress", ""+progress);
songProgressBar.setProgress(progress);
// Running this thread after 100 milliseconds
mHandler.postDelayed(this, 100);
}
};
/**
*
* */
@Override
public void onProgressChanged(SeekBar seekBar, int progress, boolean fromTouch) {
}
/**
* When user starts moving the progress handler
* */
@Override
public void onStartTrackingTouch(SeekBar seekBar) {
// remove message Handler from updating progress bar
mHandler.removeCallbacks(mUpdateTimeTask);
}
/**
* When user stops moving the progress hanlder
* */
@Override
public void onStopTrackingTouch(SeekBar seekBar) {
mHandler.removeCallbacks(mUpdateTimeTask);
int totalDuration = mp.getDuration();
int currentPosition = utils.progressToTimer(seekBar.getProgress(), totalDuration);
// forward or backward to certain seconds
mp.seekTo(currentPosition);
// update timer progress again
updateProgressBar();
}
/**
* On Song Playing completed
* if repeat is ON play same song again
* if shuffle is ON play random song
* */
@Override
public void onCompletion(MediaPlayer arg0) {
// check for repeat is ON or OFF
if(isRepeat){
// repeat is on play same song again
playSong(currentSongIndex);
} else if(isShuffle){
// shuffle is on - play a random song
Random rand = new Random();
currentSongIndex = rand.nextInt((songsList.size() - 1) - 0 + 1) + 0;
playSong(currentSongIndex);
} else{
// no repeat or shuffle ON - play next song
if(currentSongIndex < (songsList.size() - 1)){
playSong(currentSongIndex + 1);
currentSongIndex = currentSongIndex + 1;
}else{
// play first song
playSong(0);
currentSongIndex = 0;
}
}
}
@Override
public void onDestroy(){
super.onDestroy();
mp.release();
}
}
这是错误：
04-16 02:53:03.652 23194-23194/? I/art: Late-enabling -Xcheck:jni
04-16 02:53:03.680 23194-23199/? I/art: Debugger is no longer active
04-16 02:53:03.714 23194-23194/? W/System: ClassLoader referenced unknown path: /data/app/com.example.mudit.take6-1/lib/arm
04-16 02:53:03.795 23194-23194/? D/AndroidRuntime: Shutting down VM
04-16 02:53:03.796 23194-23194/? E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.mudit.take6, PID: 23194
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.mudit.take6/com.example.mudit.take6.AndroidBuildingMusicPlayerActivity}: java.lang.NullPointerException: Attempt to get length of null array
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2426)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2490)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1354)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5443)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:728)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
Caused by: java.lang.NullPointerException: Attempt to get length of null array
at com.example.mudit.take6.SongsManager.getPlayList(SongsManager.java:28)
at com.example.mudit.take6.AndroidBuildingMusicPlayerActivity.onCreate(AndroidBuildingMusicPlayerActivity.java:85)
at android.app.Activity.performCreate(Activity.java:6259)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1130)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2379)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2490)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1354)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5443)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:728)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
你能帮助我，告诉我是否实施了正确的代码。 任何帮助都会得到赞赏。
答案 0 :(得分：0)
我认为您的错误日志显示清楚：
引起：java.lang.NullPointerException：尝试获取null数组的长度 在com.example.mudit.take6.SongsManager.getPlayList（SongsManager.java:28）
if (home.listFiles(new FileExtensionFilter()).length > 0) {}
此处 home.listFiles（new FileExtensionFilter（））为空。请在此处添加断点以进行调试。