使用意图从ViewHolder内部启动活动会使应用程序崩溃

Question

I am trying to call another activity using Intent - the code generates a list of cards and I want the user to be able to edit a card by clicking it. The rest of the code works fine but the app crashes when I click a card.

public class NoteCardAdapter extends RecyclerView.Adapter<NoteCardAdapter.NoteCardViewHolder> {

    private Context mCtx;
    private List<NoteCard> noteCardList;

    public NoteCardAdapter(Context mCtx, List<NoteCard> noteCardList) {
        this.mCtx = mCtx;
        this.noteCardList = noteCardList;
    }

    @Override
    public NoteCardViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {

        LayoutInflater inflater = LayoutInflater.from(mCtx);
        View view = inflater.inflate(R.layout.note_layout, null);
        return new NoteCardViewHolder(view);

    }

    @Override
    public void onBindViewHolder(final NoteCardViewHolder holder, int position) {

        final NoteCard noteCard = noteCardList.get(position);

        holder.noteCardTitle.setText(noteCard.getNoteCardTitle());
        holder.noteCardSummary.setText(noteCard.getNoteCardSummary());
    }

    @Override
    public int getItemCount() {
        return noteCardList.size();
    }



    class NoteCardViewHolder extends RecyclerView.ViewHolder {

        public TextView noteCardTitle, noteCardSummary;
        public LinearLayout linearLayout;


        private AdapterView.OnItemClickListener itemClickListener;

        public NoteCardViewHolder(final View itemView) {
            super(itemView);

            noteCardTitle = itemView.findViewById(R.id.noteTitleView);
            noteCardSummary = itemView.findViewById(R.id.noteSummaryView);
            linearLayout = itemView.findViewById(R.id.linearLayout);

            itemView.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View view) {

//THIS IS WHERE THE APP CRASHES

                    itemView.getContext().startActivity(new Intent(itemView.getContext(), NoteEdit.class));
                }
            });
        }
    }
}

The crash log reads:

E/AndroidRuntime: FATAL EXCEPTION: main
                  Process: com.dlimited.mydolist, PID: 4007
                  java.lang.RuntimeException: Unable to start activity ComponentInfo{com.dlimited.mydolist/com.dlimited.mydolist.NoteEdit}: java.lang.NullPointerException
                      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
                      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
                      at android.app.ActivityThread.access$800(ActivityThread.java:135)
                      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
                      at android.os.Handler.dispatchMessage(Handler.java:102)
                      at android.os.Looper.loop(Looper.java:136)
                      at android.app.ActivityThread.main(ActivityThread.java:5017)
                      at java.lang.reflect.Method.invokeNative(Native Method)
                      at java.lang.reflect.Method.invoke(Method.java:515)
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
                      at dalvik.system.NativeStart.main(Native Method)
                   Caused by: java.lang.NullPointerException
                      at com.dlimited.mydolist.NoteEdit.onCreate(NoteEdit.java:31)
                      at android.app.Activity.performCreate(Activity.java:5231)
                      at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
                      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
                      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245) 
                      at android.app.ActivityThread.access$800(ActivityThread.java:135) 
                      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196) 
                      at android.os.Handler.dispatchMessage(Handler.java:102) 
                      at android.os.Looper.loop(Looper.java:136) 
                      at android.app.ActivityThread.main(ActivityThread.java:5017) 
                      at java.lang.reflect.Method.invokeNative(Native Method) 
                      at java.lang.reflect.Method.invoke(Method.java:515) 
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779) 
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595) 
                      at dalvik.system.NativeStart.main(Native Method) 

Any help will be much appreciated.

Answer 1

First things first. When you have those kind of problems, please, also post the crash's log, so we can help you with more accuracy.

Let me get that straight, you want to call an activity when you click on a Recyclerview's list, right? Yes, it should work, if you this right. You can implement a click listener with your ViewHolder and override the onClick method..

 class NoteCardViewHolder extends RecyclerView.ViewHolder 
                 iplements View.onClickListener {
 ....
    @Override
    public void onClick(View view) {

       Intent intent = new Intent(getActivity(), YourActivity.class);
       startActivity(intent);

    }
 }

Answer 2

use the mCtx you have above.

            mCtx.startActivity(new Intent(mCtx, NoteEdit.class));

Edit:

after adding your logcat. the problem is not in your activity. it's in the second activity

Answer 3

You should not starting the activity from Adapter. An Adapter should only handling the view for each item in the data set. All related to the item view in adapter can be done in it but no more.

You need to use Callback/Listener to tell the Activity or Fragment where Adapter reside to start the Activity.

Add a listener to your adapter, something like this:

public class NoteCardAdapter extends RecyclerView.Adapter<NoteCardAdapter.NoteCardViewHolder> {

    private Listener mListener;
    public interface Listener {
      void itemClicked();
    }

    ...

    public NoteCardAdapter(Listener, listener, List<NoteCard> noteCardList) {
        this.mListener = listener;
        this.noteCardList = noteCardList;
    }

    ...

    class NoteCardViewHolder extends RecyclerView.ViewHolder {
      ...
      public NoteCardViewHolder(final View itemView) {
        super(itemView);
        ...

        itemView.setOnClickListener(new View.OnClickListener() {
          @Override
          public void onClick(View view) {
            mListener.itemClicked();
          }
        });
      }
    }
    ...
}

Then in your Activity caller you need to implement the listener for Adapter:

NoteCardAdapter.Listener listener = new NoteCardAdapter.Listener() {
      @Override public void onItemClicked() {
        // start the activity here.
        startActivity(new Intent(YourActivity.this, NoteEdit.class));
      }
    });

NoteCardAdapter adapter = new NoteCardAdapter(listener, noteCardList);