Edit: I realize this has been marked as a duplicate. But I believe this is somewhat different because I am not asking what a Null Pointer Exception is or how to fix it on a "programming fundamentals" level. If I am wrong on that then please correct me, but I believe that my question touches on a more intricate matter dealing with the Android framework. My issue has I have been trying to create a simple media player app following a basic YouTube tutorial but the app continues to force close immediately upon opening in the emulator. I am assuming it is some sort of configuration error because I have followed the tutorial to the letter. I have updated my code snippets according to the advice given. In the emulator the app force closes, however when I run the device on my phone the toast message "Null Array" is shown. My question, therefore, is why the program is not adding items into the mySongs ArrayList because there are .mp3 files in both the internal and external storage directories of my device. My code is as follows....
MainActivity.java:
public class MainActivity extends AppCompatActivity
{
ListView lv;
String[] items;
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
lv = (ListView) findViewById(R.id.lvPlaylist);
final ArrayList<File> mySongs = findSongs(Environment.getExternalStorageDirectory());
items = new String[mySongs.size()];
if (mySongs != null && !mySongs.isEmpty())
{
for (int i = 0; i < mySongs.size(); i++)
{
//toast(mySongs.get(i).getName().toString());
items[i] = mySongs.get(i).getName().toString().replace("mp3", "").replace(".wav", "");
}
}
else
{
//Log.e(getString(R.string.Exception));
Toast.makeText(this, "Null Array", Toast.LENGTH_SHORT).show();
}
ArrayAdapter<String> adp = new ArrayAdapter<String>(getApplicationContext(), R.layout.song_layout, R.id.textView,items);
lv.setAdapter(adp);
lv.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
startActivity(new Intent(getApplicationContext(), Player.class).putExtra("pos", position).putExtra("songlist", mySongs));
}
});
}
public ArrayList<File> findSongs(File root)
{
ArrayList<File> al = new ArrayList<File>();
File[] files = root.listFiles();
for (File singleFile : files)
{
if (singleFile.isDirectory() && !singleFile.isHidden())
{
findSongs(singleFile);
}
else
{
if (singleFile.getName().endsWith(".mp3") || singleFile.getName().endsWith(".wav"))
{
al.add(singleFile);
}
}
}
return al;
}
activity_main.xml:
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.example.user.mediaplayer.MainActivity">
<ListView
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:id="@+id/lvPlaylist"
android:layout_centerHorizontal="true"
android:layout_alignParentTop="true" />
</RelativeLayout>
The log file:
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.user.mediaplayer/com.example.user.mediaplayer.MainActivity}: java.lang.NullPointerException: Attempt to get length of null array
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: java.lang.NullPointerException: Attempt to get length of null array
at com.example.user.mediaplayer.MainActivity.findSongs(MainActivity.java:42)
at com.example.user.mediaplayer.MainActivity.onCreate(MainActivity.java:28)
at android.app.Activity.performCreate(Activity.java:6237)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
I have also included:
uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"
uses-permission android:name="android.permission.STORAGE"
uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"
in the AndroidManifest.xml file. Any advice in the right direction would be appreciated. Thanks...
