Android

I'm looking for a way to implement a simple list view scrolling in my Firebase app, but I am not getting any way out how to implement this. I have already tried 2-3 tutorials and documentation available on the Internet, but didn't the required result.

In my app I want scrolling like at starting first 10 list items load then each time on scrolling next 10 or 20 items will load until the last item appears at the bottom of the list.

So I tried retrieving first 10 items the following way :



<pre>private void readsposts(){

        DatabaseReference reference = FirebaseDatabase.getInstance().getReference();
        reference.keepSynced(true);

        reference.child("Posts")
                .limitToLast(10)
                .addValueEventListener(new ValueEventListener() {
                    @Override
                    public void onDataChange(DataSnapshot dataSnapshot) {
                       
                        postList.clear();
                        for(DataSnapshot snapshot:dataSnapshot.getChildren()){
                            Post post = snapshot.getValue(Post.class);
                            for(String id:followingList){

                                if(post.getPublisher()!=null && post.getPublisher().equals(id)){

                                    postList.add(post);
                                   

                                }

                            }

                            if(post.getPublisher()!=null && post.getPublisher().equals(firebaseUser.getUid())){
                                postList.add(post);

                            }

                            postAdapter.notifyDataSetChanged();


                        }
                        
                        mProgressBar.setVisibility(RecyclerView.GONE);

                    }


                    @Override public void onCancelled(DatabaseError databaseError) {
                        mProgressBar.setVisibility(RecyclerView.GONE);
                    }
                });
    }

AndroidEnvironment.UnhandledExceptionRaiser += (sender, e) => ...
TaskScheduler.UnobservedTaskException += (sender, e) => ...
AppDomain.CurrentDomain.UnhandledException += (sender, e) => ...

throw 0xBEEF;

@Override
protected void onCreate(Bundle savedInstanceState) {
    layoutHomeButton = findViewById(R.id.layoutHomeButton);
    layoutHomeButton.setOnClickListener(new View.OnClickListener() {  //  <===exception here
                @Override
                public void onClick(View view) {
                   // my code goes here
                }
            });
}

java.lang.RuntimeException: 
  at android.app.ActivityThread.performLaunchActivity (ActivityThread.java:3021)
  at android.app.ActivityThread.handleLaunchActivity (ActivityThread.java:3156)
  at android.app.servertransaction.LaunchActivityItem.execute (LaunchActivityItem.java:78)
  at android.app.servertransaction.TransactionExecutor.executeCallbacks (TransactionExecutor.java:108)
  at android.app.servertransaction.TransactionExecutor.execute (TransactionExecutor.java:68)
  at android.app.ActivityThread$H.handleMessage (ActivityThread.java:1864)
  at android.os.Handler.dispatchMessage (Handler.java:106)
  at android.os.Looper.loop (Looper.java:205)
  at android.app.ActivityThread.main (ActivityThread.java:6991)
  at java.lang.reflect.Method.invoke (Native Method)
  at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run (RuntimeInit.java:493)
  at com.android.internal.os.ZygoteInit.main (ZygoteInit.java:884)
Caused by: java.lang.NullPointerException: 
  at com.hiclass.earthlivecam.publiccam.earthcam.webcamhd.ui.activities.ActivityPlayVideo.onCreate (ActivityPlayVideo.java:210)
  at android.app.Activity.performCreate (Activity.java:7159)
  at android.app.Activity.performCreate (Activity.java:7150)
  at android.app.Instrumentation.callActivityOnCreate (Instrumentation.java:1272)
  at android.app.ActivityThread.performLaunchActivity (ActivityThread.java:3001)

 @Override
 protected void onCreate(Bundle savedInstanceState) {
     super.onCreate(savedInstanceState);

     mHomeWatcher = new HomeWatcher(this);
     mHomeWatcher.setOnHomePressedListener(new OnHomePressedListener() {
         @Override
         public void onHomePressed() {
           // my code goes here
         }
         @Override
         public void onHomeLongPressed() {
           // my code goes here
         }
     });
     mHomeWatcher.startWatch();
}

 protected void stopHomeWatcher(){
     if(mHomeWatcher != null) {
         mHomeWatcher.stopWatch();
         mHomeWatcher.setOnHomePressedListener(null);
         mHomeWatcher = null;
     }
 }

public class HomeWatcher {
    public HomeWatcher(Context context) {
        mContext = context;
        mFilter = new IntentFilter(Intent.ACTION_CLOSE_SYSTEM_DIALOGS);
    }

    public void setOnHomePressedListener(OnHomePressedListener listener) {
        mListener = listener;
        mReceiver = new InnerReceiver();
    }

    public void startWatch() {
        if (mReceiver != null) {
            mContext.registerReceiver(mReceiver, mFilter);
        }
    }

   /* EXCEPTION IN THIS FUNCTION */
    public void stopWatch() {
        if (mReceiver != null) {
            if(mContext != null)
                mContext.unregisterReceiver(mReceiver);// <<==========THIS IS WHERE I GET EXCEPTION
        }
    }

    class InnerReceiver extends BroadcastReceiver {
        final String SYSTEM_DIALOG_REASON_KEY = "reason";
        final String SYSTEM_DIALOG_REASON_GLOBAL_ACTIONS = "globalactions";
        final String SYSTEM_DIALOG_REASON_RECENT_APPS = "recentapps";
        final String SYSTEM_DIALOG_REASON_HOME_KEY = "homekey";

        @Override
        public void onReceive(Context context, Intent intent) {
            String action = intent.getAction();
            if (action.equals(Intent.ACTION_CLOSE_SYSTEM_DIALOGS)) {
                String reason = intent.getStringExtra(SYSTEM_DIALOG_REASON_KEY);
                if (reason != null) {
                    if(reason.trim().toLowerCase().equals("homekey")) {
                      // my code goes here
                    }
                }
            }
        }
    }
}

java.lang.IllegalArgumentException: 
  at android.app.LoadedApk.forgetReceiverDispatcher (LoadedApk.java:1012)
  at android.app.ContextImpl.unregisterReceiver (ContextImpl.java:1360)
  at android.content.ContextWrapper.unregisterReceiver (ContextWrapper.java:608)
  at com.hiclass.earthlivecam.publiccam.earthcam.webcamhd.utils.HomeWatcher.stopWatch (HomeWatcher.java:39)
  at com.hiclass.earthlivecam.publiccam.earthcam.webcamhd.ui.activities.ActivityBase.stopHomeWatcher (ActivityBase.java:442)
  at com.hiclass.earthlivecam.publiccam.earthcam.webcamhd.ui.activities.ActivityMain.access$301 (ActivityMain.java:77)
  at com.hiclass.earthlivecam.publiccam.earthcam.webcamhd.ui.activities.ActivityMain$15.onClick (ActivityMain.java:911)
  at android.view.View.performClick (View.java:5703)
  at android.view.View$PerformClick.run (View.java:22811)
  at android.os.Handler.handleCallback (Handler.java:836)
  at android.os.Handler.dispatchMessage (Handler.java:103)
  at android.os.Looper.loop (Looper.java:203)
  at android.app.ActivityThread.main (ActivityThread.java:6297)