change data in recyclerview

Question

Seems like I still can't get hold of how notifydatasetchanged works. I tried to update a variable in adapter, but couldn't do it successfully. I tried like below, also tried to define separate class Nav Drawer items, but just couldn't do anything.

Basically, the count should be updated time to time, so I just need to update that in NavDrawer. Definitely I have some misunderstanding how notifydatasetchanged works.

I am pretty much sure I did some thing similar to METHOD 2 using ListView in past. Only difference was, I used an ArrayList in that case, but here I am directly storing arrays inside NavDrawerList and pass that to adapter.

Method 1

public class ActivityMain extends AppCompatActivity{

    private String[] navMenuTitles;
    public int count;

    RecyclerView mRecyclerView;
    RecyclerView.Adapter mAdapter;
    RecyclerView.LayoutManager mLayoutManager;
    DrawerLayout mDrawerLayout;
    ActionBarDrawerToggle mDrawerToggle;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        navMenuTitles = getResources().getStringArray(R.array.nav_drawer_items);
        count = 20;

        mRecyclerView = (RecyclerView) findViewById(R.id.RecyclerView);
        mRecyclerView.setHasFixedSize(true);
        mAdapter = new NavDrawerAdapter(navMenuTitles, count);
        mRecyclerView.setAdapter(mAdapter);
        mLayoutManager = new LinearLayoutManager(this);
        mRecyclerView.setLayoutManager(mLayoutManager);
        mDrawerLayout = (DrawerLayout) findViewById(R.id.DrawerLayout);

        mDrawerToggle = new ActionBarDrawerToggle(this, mDrawerLayout, toolbar, R.string.openDrawer, R.string.closeDrawer);
        mDrawerLayout.setDrawerListener(mDrawerToggle);
    }

    public void updateCount(){
        count = 10;
        mAdapter.notifyDataSetChanged(); // DRAWER STILL SHOWS 20 EVEN IF I CALL THIS FUNCTION
    }
}





public class NavDrawerAdapter extends RecyclerView.Adapter<NavDrawerAdapter.ViewHolder> {
    private String[] mNavTitles;
    private int count;

    public NavDrawerAdapter(mNavTitles, mCount){
        this.mNavTitles = mNavTitles;
        this.count = mCount;
    }

    public class ViewHolder extends RecyclerView.ViewHolder {
        TextView textView;
        TextView counter;

        public ViewHolder (View itemView) {
            textView = (TextView) itemView.findViewById(R.id.title);
            counter = (TextView) itemView.findViewById(R.id.counter);
        }
    }

    @Override
    public NavDrawerAdapter.ViewHolder onCreateViewHolder(ViewGroup parent) {
        View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.navdrawer_item,parent,false);
        return new ViewHolder(v);
    }

    @Override
    public void onBindViewHolder(NavDrawerAdapter.ViewHolder holder, int position) {
        holder.textView.setText(mNavTitles[position]);
        holder.counter.setText("" + _count);
    }

    @Override
    public int getItemCount() {
        return mNavTitles.length;
    }
}

Method 2

    public class ActivityMain extends AppCompatActivity{

        private String[] navMenuTitles;
        private NavDrawerList navDrawerList;

        RecyclerView mRecyclerView;
        RecyclerView.Adapter mAdapter;
        RecyclerView.LayoutManager mLayoutManager;
        DrawerLayout mDrawerLayout;
        ActionBarDrawerToggle mDrawerToggle;

        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);

            navMenuTitles = getResources().getStringArray(R.array.nav_drawer_items);

            mRecyclerView = (RecyclerView) findViewById(R.id.RecyclerView);
            mRecyclerView.setHasFixedSize(true);
            mAdapter = new NavDrawerAdapter(new NavDrawerList(navMenuTitles, 20));
            mRecyclerView.setAdapter(mAdapter);
            mLayoutManager = new LinearLayoutManager(this);
            mRecyclerView.setLayoutManager(mLayoutManager);
            mDrawerLayout = (DrawerLayout) findViewById(R.id.DrawerLayout);

            mDrawerToggle = new ActionBarDrawerToggle(this, mDrawerLayout, toolbar, R.string.openDrawer, R.string.closeDrawer);
            mDrawerLayout.setDrawerListener(mDrawerToggle);
        }

        public void updateCount(){
            navDrawerList.setNavCount(10);
            mAdapter.notifyDataSetChanged(); // DRAWER STILL SHOWS 20 EVEN IF I CALL THIS FUNCTION
        }
    }





    public class NavDrawerAdapter extends RecyclerView.Adapter<NavDrawerAdapter.ViewHolder> {
        private String[] mNavTitles;
        private int count;

        public NavDrawerAdapter(mNavTitles, mCount){
            this.mNavTitles = navDrawerList.getNavTitles();
            this.count = navDrawerList.getNavCount();
        }
    }

public class NavDrawerList {
    private String[] navTitles;
    private int navCount;

    public NavDrawerList(String[] navTitles, int navCount){
        this.navTitles = navTitles;
        this.navCount = navCount;
    }

    public String[] getNavTitles(){
        return navTitles;
    }

    public int getNavCount(){
        return navCount;
    }

    public void setNavCount(int navCount){
        this.navCount = navCount;
    }
}

Answer 1

I think if i understand u correct, there is an array of strings you have with 20 values. You are passing a count (i.e number of items to show) to update number of items in the list, like 10 or 20. The problem is even if you update count the recycler view method getItemCount() is returning mNavTitles.length i.e all of them. So the whole list is made irrespective of count value. So one solution will be :

In your method 1

change

@Override
public int getItemCount() {
    return mNavTitles.length;
}

to

@Override
public int getItemCount() {
    return count;
}

also make sure the value of count is never bigger than mNavTitles.length because if so, ur code will throw index out of bounds error..

Answer 2

If you change just your list mNavTitles that won't change the adapter.

You need to change it inside adapter, just like you did in constructor:

public void updateList(String[] mNavTitles) {
    this.mNavTitles = mNavTitles;
}

And then you call notifyDataSetChanged which will work out if anything changed or added and will call appropriate onBindViewHolder or onCreateViewHolder methods.