RecyclerViewによるクラッシュヌルリファレンスのsetOnClickListenerボタン

Question

私はRecyclerView（最後のViewHolderアイテムはボタンです）にフッターボタンを追加するためのガイドとしてthisソリューションを使用していますが、私はnullオブジェクトリファレンスを取得していますアダプタクラスのonBindViewHolderボタンにonClickListenerを設定しようとしました。

私は問題がかなりシンプルだと感じています。私は多くのデバッグの後でそれを見落としていると思います。

オンクリックリスナーを設定すると、ボタンmAddChordButtonがnullになる原因を突き止めることができますか？

アダプタクラス

public class UserChordsAdapter extends RecyclerView.Adapter<UserChordsAdapter.ChordViewHolder> { 

    final private ListItemClickListener mOnClickListener; 
    private static int viewHolderCount; 
    private int mNumberItems; 

    public interface ListItemClickListener { 
     void onListItemClick(int clickedItemIndex); 
    } 


    public UserChordsAdapter(int numberOfItems, ListItemClickListener listener) { 
     ... 
    } 

    @Override 
    public ChordViewHolder onCreateViewHolder(ViewGroup parent, int viewType) { 
     ... 
     View listItem; 
     ChordViewHolder viewHolder; 

     if (viewType == R.layout.user_chord_list_item) { //item isn't last in list 
      listItem = inflater.inflate(layoutIdForListItem, parent, shouldAttachToParentImmediately); 
      viewHolder = new ChordViewHolder(listItem); 
      viewHolder.viewHolderIndex.setText("Chord " + viewHolderCount); 
     } 
     else{ //inflate "+ Add new" button for last list item 
      listItem = inflater.inflate(layoutIdForListItem, parent, shouldAttachToParentImmediately); 
      viewHolder = new ChordViewHolder(listItem); 
     } 

     viewHolderCount++; 
     return viewHolder; 
    } 

    @Override 
    public void onBindViewHolder(ChordViewHolder holder, int position) { 
     if (position == mNumberItems){ 
      holder.mAddChordButton.setOnClickListener(new View.OnClickListener(){ //ERROR HERE 
       @Override 
       public void onClick(View v) { 
        //TODO: Add New Chord into RecyclerView 
       } 
      }); 
     } 
    } 

    @Override 
    public int getItemCount() { 
     return mNumberItems + 1;// +1 is for footer button (add new) 
    } 

    class ChordViewHolder extends RecyclerView.ViewHolder 
      implements View.OnClickListener { 

     // Will display which ViewHolder is displaying this data 
     TextView viewHolderIndex; 
     public Button mAddChordButton; 

     /** 
     * Constructor for our ViewHolder. Within this constructor, we get a reference to our 
     * TextViews and set an onClickListener to listen for clicks. Those will be handled in the 
     * onClick method below. 
     */ 
     public ChordViewHolder(View itemView) { 
      super(itemView); 

      mAddChordButton = (Button) itemView.findViewById(R.id.button_add_new);  //ATTEMPT TO INITIALIZE BUTTON HERE 
      viewHolderIndex = (TextView) itemView.findViewById(R.id.tv_view_holder_instance); 
      itemView.setOnClickListener(this); 
     } 

     /** 
     * Called whenever a user clicks on an item in the list. 
     * @param v The View that was clicked 
     */ 
     @Override 
     public void onClick(View v) { 
      int clickedPosition = getAdapterPosition(); 
      mOnClickListener.onListItemClick(clickedPosition); 
     } 
    } 

    /** 
    * Distinguishes if view is a Chord list item or the last item in the list (add new chord) 
    * @param position 
    * @return 
    */ 
    @Override 
    public int getItemViewType(int position) { 
     return (position == mNumberItems) ? R.layout.user_chord_add_new : R.layout.user_chord_list_item; 
    } 
} 

Logcat

05-24 22:31:26.284 3083-7540/com.example.foo E/AndroidRuntime: FATAL EXCEPTION: main 
                   Process: com.example.foo, PID: 3083 
                   java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference 
                    at com.example.foo.UserChordsAdapter.onBindViewHolder(UserChordsAdapter.java:68) 
                    at com.example.foo.UserChordsAdapter.onBindViewHolder(UserChordsAdapter.java:15) 
                    at android.support.v7.widget.RecyclerView$Adapter.onBindViewHolder(RecyclerView.java:6067) 
                    at android.support.v7.widget.RecyclerView$Adapter.bindViewHolder(RecyclerView.java:6100) 
                    at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:5282) 
                    at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:5158) 
                    at android.support.v7.widget.LinearLayoutManager$LayoutState.next(LinearLayoutManager.java:2061) 
                    at android.support.v7.widget.LinearLayoutManager.layoutChunk(LinearLayoutManager.java:1445) 
                    at android.support.v7.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1408) 
                    at android.support.v7.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:580) 
                    at android.support.v7.widget.RecyclerView.dispatchLayoutStep2(RecyclerView.java:3379) 
                    at android.support.v7.widget.RecyclerView.onMeasure(RecyclerView.java:2906) 
                    at android.view.View.measure(View.java:19734) 
                    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6120) 
                    at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1464) 
                    at android.widget.LinearLayout.measureHorizontal(LinearLayout.java:1117) 
                    at android.widget.LinearLayout.onMeasure(LinearLayout.java:642) 
                    at android.view.View.measure(View.java:19734) 
                    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6120) 
                    at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1464) 
                    at android.widget.LinearLayout.measureVertical(LinearLayout.java:758) 
                    at android.widget.LinearLayout.onMeasure(LinearLayout.java:640) 
                    at android.view.View.measure(View.java:19734) 
                    at android.widget.LinearLayout.measureHorizontal(LinearLayout.java:1098) 
                    at android.widget.LinearLayout.onMeasure(LinearLayout.java:642) 
                    at android.view.View.measure(View.java:19734) 
                    at android.widget.LinearLayout.measureVertical(LinearLayout.java:911) 
                    at android.widget.LinearLayout.onMeasure(LinearLayout.java:640) 
                    at android.view.View.measure(View.java:19734) 
                    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6120) 
                    at android.widget.FrameLayout.onMeasure(FrameLayout.java:185) 
                    at android.view.View.measure(View.java:19734) 
                    at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2271) 
                    at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1358) 
                    at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1607) 
                    at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1246) 
                    at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6301) 
                    at android.view.Choreographer$CallbackRecord.run(Choreographer.java:871) 
                    at android.view.Choreographer.doCallbacks(Choreographer.java:683) 
                    at android.view.Choreographer.doFrame(Choreographer.java:619) 
                    at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:857) 
                    at android.os.Handler.handleCallback(Handler.java:751) 
                    at android.os.Handler.dispatchMessage(Handler.java:95) 
                    at android.os.Looper.loop(Looper.java:154) 
                    at android.app.ActivityThread.main(ActivityThread.java:6077) 
                    at java.lang.reflect.Method.invoke(Native Method) 
                    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865) 
                    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755) 

Answer 1

私は問題を解決しました。私は単にonCreateViewHolderの間違ったレイアウトを膨らませました。フッタービューの正しいレイアウトIDを宣言し、それを私のelseステートメントで膨らませた後、それはうまくいった。

正しいコードは次のとおりです。

@Override 
    public ChordViewHolder onCreateViewHolder(ViewGroup parent, int viewType) { 
     Context context = parent.getContext(); 
     int layoutIdForListItem = R.layout.user_chord_list_item; 
     int layoutIdForFooterItem = R.layout.user_chord_add_new; //SOLUTION 
     LayoutInflater inflater = LayoutInflater.from(context); 
     boolean shouldAttachToParentImmediately = false; 

     View listItem; 
     ChordViewHolder viewHolder; 

     if (viewType == R.layout.user_chord_list_item) { //inflate normal list item 
      listItem = inflater.inflate(layoutIdForListItem, parent, shouldAttachToParentImmediately); 
      viewHolder = new ChordViewHolder(listItem); 
      viewHolder.viewHolderIndex.setText("Chord " + viewHolderCount); 
     } 
     else{ //inflate "+ Add new" button for last list item 
      listItem = inflater.inflate(layoutIdForFooterItem, parent, shouldAttachToParentImmediately); 
      viewHolder = new ChordViewHolder(listItem); 
     } 

     viewHolderCount++; 
     return viewHolder; 
    }