我正在学习Android几天。在开发一个简单的音乐播放器时，我在使用setDataSource（String fileName）方法时遇到了这个异常
MainActivity.java
package com.bihan.zombieplayer;
import java.io.File;
import java.io.FileDescriptor;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.util.concurrent.TimeUnit;
import android.app.Activity;
import android.content.Intent;
import android.content.SharedPreferences;
import android.content.SharedPreferences.Editor;
import android.media.MediaPlayer;
import android.os.Bundle;
import android.os.Handler;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.ImageButton;
import android.widget.ImageView;
import android.widget.SeekBar;
import android.widget.SeekBar.OnSeekBarChangeListener;
import android.widget.TextView;
import android.widget.Toast;
public class MainActivity extends Activity implements OnClickListener, OnSeekBarChangeListener{
ImageButton list, play,next, prev, fast, rev;
TextView sn, ct, dt;
MediaPlayer mp;
SeekBar sb;
private Handler myHandler = new Handler();
SharedPreferences sp;
protected int startTime, finalTime;
String songName, songLoc;
Boolean songSet = false;
ImageView ab;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
initialize_components();
initialize_mediaPlayer();
}
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
int id = v.getId();
if(id == R.id.bt_play){
if(songSet == true)
{
if(mp.isPlaying()){
play.setImageResource(R.drawable.bt_pause);
mp.pause();
}
else{
startTime = mp.getCurrentPosition();
setTime(startTime,ct);
setTime(finalTime,dt);
sb.setProgress(startTime);
myHandler.postDelayed(UpdateSongTime, 100);
}
}
else
Toast.makeText(this, "Select a song", Toast.LENGTH_LONG).show();
}
else if(id == R.id.bt_back){
int curTime = mp.getCurrentPosition();
mp.seekTo(curTime+PlayerDetails.TIME_TO_SEEK);
}
else if(id == R.id.bt_next){
}
else if(id == R.id.bt_prev){
}
else if(id == R.id.bt_fwd){
int curTime = mp.getCurrentPosition();
mp.seekTo(curTime-PlayerDetails.TIME_TO_SEEK);
}
else if(id == R.id.bt_list){
Intent i = new Intent(this,PlayList.class);
startActivityForResult(i, PlayerDetails.REQUEST_CODE);
}
}
private void initialize_components()
{
/***
* This Funtion initializes the components on the activity
*/
list = (ImageButton)findViewById(R.id.bt_list);
play = (ImageButton)findViewById(R.id.bt_play);
next = (ImageButton)findViewById(R.id.bt_next);
prev = (ImageButton)findViewById(R.id.bt_prev);
fast = (ImageButton)findViewById(R.id.bt_fwd);
rev = (ImageButton)findViewById(R.id.bt_back);
sn = (TextView)findViewById(R.id.song_name);
ct = (TextView)findViewById(R.id.cur_time);
dt = (TextView)findViewById(R.id.dur_time);
sb = (SeekBar)findViewById(R.id.mp_seekbar);
ab = (ImageView)findViewById(R.id.album_image);
list.setOnClickListener(this);
play.setOnClickListener(this);
next.setOnClickListener(this);
prev.setOnClickListener(this);
fast.setOnClickListener(this);
rev.setOnClickListener(this);
sb.setOnSeekBarChangeListener(this);
}
private void initialize_mediaPlayer()
{
/***
* This method initializes the mediaplayer
* If no media is selected it shows the prefered media (last played music)
*/
//use sharedPreference
sp = getSharedPreferences("musicplayer", MODE_PRIVATE);
songName = sp.getString("songName","No Song Selected");
songLoc = sp.getString("songLoc","");
songSet = sp.getBoolean("songPlay", false);
if(songSet == false)
{
sn.setText(songName);
setTime(0,dt);
setTime(0,ct);
}
else
{
try{
mp.setDataSource(songLoc);
mp.prepare();
}
catch(Exception e){
Toast.makeText(this, "Some Error Occured", Toast.LENGTH_LONG).show();
}
finalTime = mp.getDuration();
setTime(mp.getDuration(),dt);
sb.setMax(mp.getDuration());
}
}
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
// TODO Auto-generated method stub
super.onActivityResult(requestCode, resultCode, data);
if(requestCode == PlayerDetails.REQUEST_CODE)
{
if(resultCode == PlayerDetails.RESULT_PLAY)
{
Bundle b = data.getExtras();
songName = b.getString("songName");
songLoc = b.getString("songLoc");
try{
Log.v("Before Data Set", songLoc);
mp.setDataSource(songLoc);
mp.prepare();
Log.v("TRY", " After Data Set");
}catch(Exception e){
Toast.makeText(this, "Some Error Occured", Toast.LENGTH_LONG).show();
e.printStackTrace();
}
/*
finalTime = mp.getDuration();
setTime(finalTime,dt);
sb.setMax(mp.getDuration());
*/
}
}
}
private Runnable UpdateSongTime = new Runnable() {
public void run() {
startTime = mp.getCurrentPosition();
setTime(startTime,ct);
sb.setProgress((int)startTime);
myHandler.postDelayed(this, 100);
}
};
private void setTime(int millis, TextView tv){
/**
* This method shows the time in time format
*/
tv.setText(String.format("%02d:%02d:%02d", TimeUnit.MILLISECONDS.toHours(millis),
TimeUnit.MILLISECONDS.toMinutes(millis) % TimeUnit.HOURS.toMinutes(1),
TimeUnit.MILLISECONDS.toSeconds(millis) % TimeUnit.MINUTES.toSeconds(1))
);
}
@Override
public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {
// TODO Auto-generated method stub
if(fromUser){
sb.setProgress(progress);
mp.seekTo(progress);
}
}
@Override
public void onStartTrackingTouch(SeekBar seekBar) {
// TODO Auto-generated method stub
mp.pause();
}
@Override
public void onStopTrackingTouch(SeekBar seekBar) {
// TODO Auto-generated method stub
mp.start();
}
@Override
protected void onDestroy() {
// TODO Auto-generated method stub
Editor e = sp.edit();
if(songSet == true){
e.putString("songName", songName);
e.putString("songLoc", songLoc);
e.putBoolean("songPlay", true);
}else{
e.remove("songName");
e.remove("songLoc");
e.remove("songPlay");
}
e.commit();
super.onDestroy();
}
}
PlayList.java
package com.bihan.zombieplayer;
import java.util.ArrayList;
import java.util.List;
import android.app.Activity;
import android.app.ListActivity;
import android.content.ContentResolver;
import android.content.Intent;
import android.database.Cursor;
import android.os.Bundle;
import android.os.Environment;
import android.provider.MediaStore;
import android.provider.MediaStore.Audio.Media;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.ListView;
public class PlayList extends ListActivity{
public List<String> songName = new ArrayList<String>();
public List<String> songLoc = new ArrayList<String>();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_play_list);
updateList();
ArrayAdapter<String> a = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1,songName);
setListAdapter(a);
}
public void updateList(){
if(isExternalStorageReadable())
{
ContentResolver cr = getContentResolver();
//Cursor c = cr.query(MediaStore.Audio.Media.INTERNAL_CONTENT_URI, null, null, null,null);
Cursor c = cr.query(MediaStore.Audio.Media.EXTERNAL_CONTENT_URI, null, null, null, null);
while(c.moveToNext()){
String name = c.getString(c.getColumnIndex(MediaStore.Audio.Media.TITLE));
songName.add(name);
String path = c.getString(c.getColumnIndex(MediaStore.Audio.Media.DATA));
songLoc.add(path);
}
}
}
public boolean isExternalStorageReadable() {
String state = Environment.getExternalStorageState();
if (Environment.MEDIA_MOUNTED.equals(state) ||
Environment.MEDIA_MOUNTED_READ_ONLY.equals(state)) {
return true;
}
return false;
}
@Override
protected void onListItemClick(ListView l, View v, int position, long id) {
// TODO Auto-generated method stub
super.onListItemClick(l, v, position, id);
String name = songName.get(position);
String path = songLoc.get(position);
Intent i = new Intent();
i.putExtra("songName", name);
i.putExtra("songLoc", path);
setResult(PlayerDetails.RESULT_PLAY,i);
finish();
}
}
和播放歌曲时的日志文件
01-15 01:26:23.662: V/Before Data Set(2883): /storage/emulated/0/media/audio/notifications/facebook_ringtone_pop.m4a
01-15 01:26:23.667: W/System.err(2883): java.lang.NullPointerException: Attempt to invoke virtual method 'void android.media.MediaPlayer.setDataSource (java.lang.String)' on a null object reference
01-15 01:26:23.668: W/System.err(2883): at com.bihan.zombieplayer.MainActivity.onActivityResult(MainActivity.java:179)
01-15 01:26:23.668: W/System.err(2883): at android.app.Activity.dispatchActivityResult(Activity.java:6442)
01-15 01:26:23.668: W/System.err(2883): at android.app.ActivityThread.deliverResults(ActivityThread.java:3716)
01-15 01:26:23.668: W/System.err(2883): at android.app.ActivityThread.handleSendResult(ActivityThread.java:3763)
01-15 01:26:23.668: W/System.err(2883): at android.app.ActivityThread.- wrap16(ActivityThread.java)
01-15 01:26:23.668: W/System.err(2883): at android.app.ActivityThread $H.handleMessage(ActivityThread.java:1403)
01-15 01:26:23.668: W/System.err(2883): at android.os.Handler.dispatchMessage(Handler.java:102)
01-15 01:26:23.668: W/System.err(2883): at android.os.Looper.loop (Looper.java:148)
01-15 01:26:23.668: W/System.err(2883): at android.app.ActivityThread.main (ActivityThread.java:5443)
01-15 01:26:23.668: W/System.err(2883): at java.lang.reflect.Method.invoke (Native Method)
01-15 01:26:23.668: W/System.err(2883): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:728)
01-15 01:26:23.668: W/System.err(2883): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
01-15 01:26:23.749: V/RenderScript(2883): 0xb887cc40 Launching thread(s), CPUs 4
01-15 01:26:27.173: E/Surface(2883): getSlotFromBufferLocked: unknown buffer: 0xb86bb240
我搜索了许多答案，但没有一个有效。
这是清单文件
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.bihan.zombieplayer"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="16"
android:targetSdkVersion="16" />
<uses-permission
android:name = "android.permission.READ_EXTERNAL_STORAGE"/>
<uses-permission
android:name = "android.permission.WRITE_EXTERNAL_STORAGE"/>
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name=".MainActivity"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name=".PlayList"
android:label="@string/title_activity_play_list" >
</activity>
</application>
</manifest>
答案 0 :(得分：0)
mp是null，因为您从未为其指定过值。