This was the code I was writing to start a Mp3Player by watching a video tutorial. I searched a lot for this issue but unable to sort out the error. After running this code , I am getting java.lang.NullPointerException error. My code looks somewhat like this:
package com.songs.playit;
import java.io.File;
import java.io.FilenameFilter;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import android.annotation.SuppressLint;
import android.app.ListActivity;
import android.media.MediaPlayer;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.ListView;
public class MainActivity extends ListActivity {
@SuppressLint("SdCardPath") private final static String sdPath = new String("/extSdCard/");
private List<String> songs = new ArrayList<String>();
MediaPlayer mp =new MediaPlayer();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.fragment_main);
updatePlaylist();
Button StopPlay = (Button) findViewById(R.id.stopBtn);
StopPlay.setOnClickListener(new OnClickListener(){
public void onClick(View v){
mp.stop();
}
});
}
private void updatePlaylist() {
// TODO Auto-generated method stub
File home = new File(sdPath);
if(home.listFiles(new Mp3Filter()).length>0){
for(File file: home.listFiles(new Mp3Filter())){
songs.add(file.getName());
}
ArrayAdapter<String> songList = new ArrayAdapter<String> (this , R.layout.songs_item , songs);
setListAdapter(songList);
}
}
protected void onListItemClick(ListView list , View v , int position , long id){
try{
mp.reset();
mp.setDataSource(sdPath + songs.get(position));
mp.prepare();
mp.start();
}
catch(IOException e){
Log.v(getString(R.string.app_name), e.getMessage());
}
}
}
class Mp3Filter implements FilenameFilter {
@Override
public boolean accept(File dir, String filename) {
// TODO Auto-generated method stub
{
return (filename.endsWith(".mp3"));
}
}
}
And this was the error I was getting :
08-13 05:06:11.630: D/dalvikvm(762): GC_FOR_ALLOC freed 43K, 4% free 2900K/3008K, paused 34ms, total 37ms
08-13 05:06:11.630: I/dalvikvm-heap(762): Grow heap (frag case) to 3.370MB for 500416-byte allocation
08-13 05:06:11.680: D/dalvikvm(762): GC_FOR_ALLOC freed 2K, 4% free 3386K/3500K, paused 40ms, total 40ms
08-13 05:06:11.780: D/AndroidRuntime(762): Shutting down VM
08-13 05:06:11.780: W/dalvikvm(762): threadid=1: thread exiting with uncaught exception (group=0xb3a3fba8)
08-13 05:06:11.800: E/AndroidRuntime(762): FATAL EXCEPTION: main
08-13 05:06:11.800: E/AndroidRuntime(762): Process: com.songs.playit, PID: 762
08-13 05:06:11.800: E/AndroidRuntime(762): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.songs.playit/com.songs.playit.MainActivity}: java.lang.NullPointerException
08-13 05:06:11.800: E/AndroidRuntime(762): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
08-13 05:06:11.800: E/AndroidRuntime(762): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
08-13 05:06:11.800: E/AndroidRuntime(762): at android.app.ActivityThread.access$800(ActivityThread.java:135)
08-13 05:06:11.800: E/AndroidRuntime(762): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
08-13 05:06:11.800: E/AndroidRuntime(762): at android.os.Handler.dispatchMessage(Handler.java:102)
08-13 05:06:11.800: E/AndroidRuntime(762): at android.os.Looper.loop(Looper.java:136)
08-13 05:06:11.800: E/AndroidRuntime(762): at android.app.ActivityThread.main(ActivityThread.java:5017)
08-13 05:06:11.800: E/AndroidRuntime(762): at java.lang.reflect.Method.invokeNative(Native Method)
08-13 05:06:11.800: E/AndroidRuntime(762): at java.lang.reflect.Method.invoke(Method.java:515)
08-13 05:06:11.800: E/AndroidRuntime(762): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
08-13 05:06:11.800: E/AndroidRuntime(762): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
08-13 05:06:11.800: E/AndroidRuntime(762): at dalvik.system.NativeStart.main(Native Method)
08-13 05:06:11.800: E/AndroidRuntime(762): Caused by: java.lang.NullPointerException
08-13 05:06:11.800: E/AndroidRuntime(762): at com.songs.playit.MainActivity.updatePlaylist(MainActivity.java:47)
08-13 05:06:11.800: E/AndroidRuntime(762): at com.songs.playit.MainActivity.onCreate(MainActivity.java:32)
08-13 05:06:11.800: E/AndroidRuntime(762): at android.app.Activity.performCreate(Activity.java:5231)
08-13 05:06:11.800: E/AndroidRuntime(762): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
08-13 05:06:11.800: E/AndroidRuntime(762): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
08-13 05:06:11.800: E/AndroidRuntime(762): ... 11 more
08-13 05:06:18.430: I/Process(762): Sending signal. PID: 762 SIG: 9
Please help me out. Thanks in advance
There is no guarantee that the path to the SD card will be /extSdCard/
If you want to get the path to the external storage you should use Environment.getExternalStorageDirectory().getAbsolutePath()
So if no file is found at path /extSdCard/ home will be null
And when you try to call home.listFiles(new Mp3Filter()) you will get a NullPointerException as you are trying to call the litFiles method on a null object
So change
private final static String sdPath = new String("/extSdCard/");
to
private final static String sdPath = new String(Environment.getExternalStorageDirectory().getAbsolutePath());
Also if you are not sure that whether a file exists or not use exists() method of the File to check