Nrthugu

I am trying to select recyclerview item randomly with delay.I need to start random selection method after fragment load without any user interaction,But getting the following error. Afterward I put it on ImageView click to check but again I am getting same exception.Will anybody here tell me where I am making a mistake,or what else could be better way to achieve this.Below is my code

    package com.apponative.bjja.fragments;



import android.os.Bundle;

import android.os.Handler;

import android.support.annotation.Nullable;

import android.support.v4.app.Fragment;

import android.support.v7.widget.GridLayoutManager;

import android.support.v7.widget.RecyclerView;

import android.view.LayoutInflater;

import android.view.View;

import android.view.ViewGroup;



import com.apponative.bjja.R;

import com.apponative.bjja.adapters.AttackGridAdapter;



import java.util.Random;



public class Fragment_AttackGrid extends Fragment {



    View v;

    RecyclerView grid_attack;

    AttackGridAdapter attackGridAdapter;

    Bundle b;

    int itemCount;

    Handler randomHandler;

    Runnable randomRunnable;

    Random rand;

    int randomNum = 0;

    long emptyTime;



    @Nullable

    @Override

    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {



        v = inflater.inflate(R.layout.fragment_attack_grid, container, false);



        setUpViews();



        return v;

    }



    void setUpViews() {



        b = getArguments();

        itemCount = b.getInt(getString(R.string.item_count));

        rand = new Random();

        randomHandler = new Handler();



        grid_attack = (RecyclerView) v.findViewById(R.id.attack_grid);

        RecyclerView.LayoutManager layoutManager = new GridLayoutManager(getActivity(), 4);



        grid_attack.setLayoutManager(layoutManager);

        attackGridAdapter = new AttackGridAdapter(getActivity(), itemCount);

        grid_attack.setAdapter(attackGridAdapter);



        v.findViewById(R.id.belt_black).setOnClickListener(new View.OnClickListener() {

            @Override

            public void onClick(View view) {

                selectRandomly();

            }

        });

    }



    void selectRandomly() {



        for (int i = 0; i < itemCount; i++) {

            emptyTime = emptyTime+1000;

            randomRunnable = new Runnable() {

                @Override

                public void run() {

                    grid_attack.findViewHolderForAdapterPosition(randomNum).itemView.setSelected(false);

                    randomNum = rand.nextInt((itemCount - 0) + 1) + 0;

                    grid_attack.findViewHolderForAdapterPosition(randomNum).itemView.setSelected(true);

                }

            };

            randomHandler.postDelayed(randomRunnable, emptyTime);



        }

        emptyTime = emptyTime+2000;

        randomRunnable = new Runnable() {

            @Override

            public void run() {

                grid_attack.findViewHolderForAdapterPosition(randomNum).itemView.performClick();

            }

        };

        randomHandler.postDelayed(randomRunnable, emptyTime);

    }



    @Override

    public void onResume() {

        super.onResume();

        //   selectRandomly();

    }

}

At start I put

selectRandomly()

at

onResume()

method and I was getting an exception:

01-27 18:28:44.969 19041-19041/com.apponative.bjja E/AndroidRuntime: FATAL EXCEPTION: main

Process: com.apponative.bjja, PID: 19041

java.lang.NullPointerException: Attempt to read from field 'android.view.View android.support.v7.widget.RecyclerView$ViewHolder.itemView' on a null object reference                                                                                      at com.apponative.bjja.fragments.Fragment_AttackGrid$2.run(Fragment_AttackGrid.java:77)

    at android.os.Handler.handleCallback(Handler.java:739)

    at android.os.Handler.dispatchMessage(Handler.java:95)

    at android.os.Looper.loop(Looper.java:155)

    at android.app.ActivityThread.main(ActivityThread.java:5696)

    at java.lang.reflect.Method.invoke(Native Method)

    at java.lang.reflect.Method.invoke(Method.java:372)

    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1028)

    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:823)

According to fragment lifecycle at Fragment LifeCycle onResume() and onStart() methods are called after view has been created. I tried putting my method there too, But no success.

It is possible that view still not loaded, which is why it is returning null exception.

This function might be useful to call when fragment is loaded and visible to the user:

// create boolean for checking if view is seen

private boolean isViewShown = false;



@Override

public void setUserVisibleHint(boolean isVisibleToUser) {

    super.setUserVisibleHint(isVisibleToUser);

    if (getView() != null) {

        isViewShown = true;

        // call your function

    } else {

        isViewShown = false;

    }

} 

This may happen if your onCreateViewHolder method returns null