I am making an app music player in Android Studio. After the installation was finished, an app on opening asks for media permission. The problem occurs after permission is granted, the app automatically closes.
I don't know why, but I found in logcat following message NullPointerException : Attempt to get length of null array
My class is :
public class MainActivity extends AppCompatActivity {
ListView listView;
String[] items;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
listView = (ListView)findViewById(R.id.listView);
runtimePermission();
}
public void runtimePermission()
{
Dexter.withContext(this).withPermission(Manifest.permission.READ_EXTERNAL_STORAGE)
.withListener(new PermissionListener() {
@Override
public void onPermissionGranted(PermissionGrantedResponse permissionGrantedResponse) {
displaySong();
}
@Override
public void onPermissionDenied(PermissionDeniedResponse permissionDeniedResponse) {
}
@Override
public void onPermissionRationaleShouldBeShown(PermissionRequest permissionRequest, PermissionToken permissionToken) {
permissionToken.continuePermissionRequest();
}
}).check();
}
public ArrayList<File> findSong(File file)
{
ArrayList<File> arrayList = new ArrayList<>();
File[] files = file.listFiles();
assert files != null;
for (File singleFile : files) {
if (singleFile.isDirectory() && !singleFile.isHidden()) {
arrayList.addAll(findSong(singleFile));
} else {
if (singleFile.getName().endsWith(".mp3") || singleFile.getName().endsWith(".wav")) {
arrayList.add(singleFile);
}
}
}
return arrayList;
}
void displaySong()
{
final ArrayList<File> mySongs = findSong(Environment.getStorageDirectory());
items = new String[mySongs.size()];
for (int i=0;i<mySongs.size();i++)
{
items[i] = mySongs.get(i).getName().toString().replace(".mp3","").replace(".wav","");
}
customAdapter customAdapter = new customAdapter();
listView.setAdapter(customAdapter);
}
class customAdapter extends BaseAdapter
{
@Override
public int getCount() {
return items.length;
}
@Override
public Object getItem(int i) {
return null;
}
@Override
public long getItemId(int i) {
return 0;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
View view = getLayoutInflater().inflate(R.id.list_item,null);
TextView txtSong = view.findViewById(R.id.txtSong);
txtSong.setSelected(true);
txtSong.setText(items[position]);
return view;
}
}
}
Where I can found issue?
here is logcat
2021-08-05 22:17:03.244 22457-22457/com.devilteched.rexplayer E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.devilteched.rexplayer, PID: 22457
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.devilteched.rexplayer/com.devilteched.rexplayer.MainActivity}: java.lang.NullPointerException: Attempt to get length of null array
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3550)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3710)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2139)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:236)
at android.app.ActivityThread.main(ActivityThread.java:8047)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:600)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:967)
Caused by: java.lang.NullPointerException: Attempt to get length of null array
at com.devilteched.rexplayer.MainActivity.findSong(MainActivity.java:66)
at com.devilteched.rexplayer.MainActivity.findSong(MainActivity.java:68)
at com.devilteched.rexplayer.MainActivity.findSong(MainActivity.java:68)
at com.devilteched.rexplayer.MainActivity.displaySong(MainActivity.java:79)
at com.devilteched.rexplayer.MainActivity$1.onPermissionGranted(MainActivity.java:46)
at com.karumi.dexter.MultiplePermissionsListenerToPermissionListenerAdapter.onPermissionsChecked(Unknown Source:35)
at com.karumi.dexter.DexterInstance$1.run(Unknown Source:43)
at com.karumi.dexter.MainThread.execute(Unknown Source:6)
at com.karumi.dexter.DexterInstance.checkMultiplePermissions(Unknown Source:71)
at com.karumi.dexter.DexterInstance.checkPermissions(Unknown Source:0)
at com.karumi.dexter.Dexter.check(Unknown Source:10)
at com.devilteched.rexplayer.MainActivity.runtimePermission(MainActivity.java:58)
at com.devilteched.rexplayer.MainActivity.onCreate(MainActivity.java:37)
at android.app.Activity.performCreate(Activity.java:8126)
at android.app.Activity.performCreate(Activity.java:8098)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1310)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3523)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3710)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2139)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:236)
at android.app.ActivityThread.main(ActivityThread.java:8047)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:600)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:967)
2021-08-05 22:17:03.248 22457-22457/com.devilteched.rexplayer D/OOMEventManagerFK: checkEventAndDumpForJE: 0 2021-08-05 22:17:03.276 22457-22457/com.devilteched.rexplayer I/Process: Sending signal. PID: 22457 SIG: 9
