add SharedPreferences to items in Recycler adapter

Question

I want to be able to check in other Activities if items in the RecyclerView are checked and don't know how to do that. I tried it with SharedPreferences, but only get an null object reference.

java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.SharedPreferences android.content.Context.getSharedPreferences(java.lang.String, int)' on a null object reference
        at com.icedex.lolmon.testapp.firststart.FirstStartRecyclerAdapter$ViewHolder.<init>(FirstStartRecyclerAdapter.java:63)
        at com.icedex.lolmon.testapp.firststart.FirstStartRecyclerAdapter.onCreateViewHolder(FirstStartRecyclerAdapter.java:35)
        at com.icedex.lolmon.testapp.firststart.FirstStartRecyclerAdapter.onCreateViewHolder(FirstStartRecyclerAdapter.java:18)
        at android.support.v7.widget.RecyclerView$Adapter.createViewHolder(RecyclerView.java:5116)
        at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:4416)
        at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:4326)
        at android.support.v7.widget.LinearLayoutManager$LayoutState.next(LinearLayoutManager.java:1955)
        at android.support.v7.widget.GridLayoutManager.layoutChunk(GridLayoutManager.java:437)
        at android.support.v7.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1327)
        at android.support.v7.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:556)
        at android.support.v7.widget.GridLayoutManager.onLayoutChildren(GridLayoutManager.java:171)
        at android.support.v7.widget.RecyclerView.dispatchLayout(RecyclerView.java:2713)
        at android.support.v7.widget.RecyclerView.onLayout(RecyclerView.java:3011)
        at android.view.View.layout(View.java:15671)
        at android.view.ViewGroup.layout(ViewGroup.java:5038)
        at android.support.v4.view.ViewPager.onLayout(ViewPager.java:1626)
        at android.view.View.layout(View.java:15671)
        at android.view.ViewGroup.layout(ViewGroup.java:5038)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:579)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:514)
        at android.view.View.layout(View.java:15671)
        at android.view.ViewGroup.layout(ViewGroup.java:5038)
        at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1703)
        at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1557)
        at android.widget.LinearLayout.onLayout(LinearLayout.java:1466)
        at android.view.View.layout(View.java:15671)
        at android.view.ViewGroup.layout(ViewGroup.java:5038)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:579)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:514)
        at android.view.View.layout(View.java:15671)
        at android.view.ViewGroup.layout(ViewGroup.java:5038)
        at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:2086)
        at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1843)
        at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1061)
        at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5885)
        at android.view.Choreographer$CallbackRecord.run(Choreographer.java:767)
        at android.view.Choreographer.doCallbacks(Choreographer.java:580)
        at android.view.Choreographer.doFrame(Choreographer.java:550)
        at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:753)
        at android.os.Handler.handleCallback(Handler.java:739)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:135)
        at android.app.ActivityThread.main(ActivityThread.java:5254)
        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:903)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)

This is my Code:

public class FirstStartRecyclerAdapter extends RecyclerView.Adapter<FirstStartRecyclerAdapter.ViewHolder> {

public static final String TAG = "FSRecyclerAdapter";
public ArrayList<Card> cards;
public Context context;

public SharedPreferences sharedPref;

public boolean checkMusic = false;

public FirstStartRecyclerAdapter(Context context, ArrayList<Card> cards) {
    this.cards = cards;
    this.context = context;
}

@Override
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    View itemView = LayoutInflater.from(parent.getContext()).inflate(R.layout.item, parent, false);

    return new ViewHolder(itemView);
}

@Override
public void onBindViewHolder(FirstStartRecyclerAdapter.ViewHolder holder, int position) {

    Card card = cards.get(position);
    holder.card_tv.setText(card.cardName);
    holder.card_iv.setImageResource(card.getDrawable());
    holder.card_iv2.setImageResource(card.getDrawable2());
}

public int getItemCount() {
        return cards.size();
}

public class ViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener {

    public ImageView card_iv;
    public ImageView card_iv2;
    public TextView card_tv;

    public ViewHolder(View itemView) {
        super(itemView);
        card_tv = (TextView) itemView.findViewById(R.id.card_tv);
        card_iv = (ImageView) itemView.findViewById(R.id.card_iv);
        card_iv2 = (ImageView) itemView.findViewById(R.id.card_iv2);

        itemView.setOnClickListener(this);
    }

    @Override
    public void onClick(View view) {
        int position = getLayoutPosition();
        Log.d(TAG, "clicked position:" + position);
        long postId = cards.get(position).getId();

        sharedPref = context.getSharedPreferences("myPref", Context.MODE_PRIVATE);
        SharedPreferences.Editor edit = sharedPref.edit();

        edit.putBoolean("checkWear", false);
        edit.apply();

        if (postId == 1) {

            if (sharedPref.getBoolean("checkWear", true)) {
                card_iv2.setImageResource(R.drawable.checkbox_blank_circle_outline);
                edit.putBoolean("checkWear", false);
                edit.apply();
            } else {
                card_iv2.setImageResource(R.drawable.checkbox_marked_circle);
                edit.putBoolean("checkWear", true);
                edit.apply();
            }
        }

        if (postId == 2) {

            if (checkMusic) {
                card_iv2.setImageResource(R.drawable.checkbox_blank_circle_outline);
                checkMusic = false;
            } else {
                card_iv2.setImageResource(R.drawable.checkbox_marked_circle);
                checkMusic = true;
            }
         }
      }
   }
}

I would appreciate any help.

Answer 1

This is what I did. (If you cant access class "context" inside SharedPreferences) 1. Create a context of the adapter class by " Context mConext"; or "private WeakReference mContext;" 2. Instead giving "mContext" use "this.mContext.get()" wherever you need to use context inside the SharedPrefernce. like SharedPreferences preferences = this.mContext.get().getSharedPreferences(MY_PREFERENCE_NAME, Context.MODE_PRIVATE);

I tried so many other solutions, but couldn't find the thing.

Answer 2

That Nullpointer looks weird to me... Anyway here's another approach:

Create a static class holding the state

final class State{  
  static boolean somethingIsChecked = false;  

  static boolean isSomethingChecked(){  
    return somethingIsChecked;  
  }  

  static void setSomethingIsChecked(boolean isChecked){  
    somethingIsChecked = isChecked;  
  }
}

Then call in your ViewHolders onClick

State.setSomethingIsChecked(somevalue);

Other Activites now can call

State.isSomethingClicked();

to get the value

---

Note that neither the Sharedpreferences nor the static class can handle multiple instances pointing to the same variable, so you should assure in your App structure that these are always singleInstance.