通过活动在片段之间进行通

Question

我有两个片段FGames和FGamesDetail。显示游戏列表，单击时应填充FGamesDetail片段。我正在使用MVP模式。

我正在尝试为平板电脑实现MultiPane布局，使列表和详细视图彼此相邻。

我在＆＃39; mListener.onGameSelected（gameEntity）中得到一个空指针异常;＆＃39;在FGames。我知道我没有在这个地方初始化它，但是我应该按照MVP模式中的每个方法初始化它。

GamesAdapter - RecyclerView Adapter。

      @OnClick(R.id.row_container)
            void rowClick(){
                GamesPresenter gamesPresenter = new GamesPresenterImpl();
                gamesPresenter.showGameDetail(data.get(getLayoutPosition()));
                Toast.makeText(context, "itemClicked " + data.get(getLayoutPosition()), Toast.LENGTH_SHORT).show();
            }

GamesPresenter - 界面

    public interface GamesPresenter {
        void initUi();
        void showGameDetail(GameEntity gameEntity);

    }

GamesPresenterImpl -

    public class GamesPresenterImpl implements GamesPresenter {

    GamesView gamesView;
    private ApiInterface apiInterface;
    /**
     * Collects all subscriptions to unsubscribe later
     */
    @NonNull
    private CompositeDisposable mCompositeDisposable = new CompositeDisposable();

    public GamesPresenterImpl() {}

    public GamesPresenterImpl(GamesView gamesView) {
        this.gamesView = gamesView;
    }

    @Override
    public void initUi() {
        getGamesData();
    }

    @Override
    public void showGameDetail(GameEntity gameEntity) {
       //gamesView was null so initialised here
        GamesView gamesView = new FGames();
        gamesView.onListItemClick(gameEntity);

      }    
    }

GamesView - 界面

    public interface GamesView {

        /**
         * Initialise the recycler view to list Games data
         * @param gameEntities
         */
        void initRecyclerView(List<GameEntity> gameEntities);

        void showToast(String message);

        void onListItemClick(GameEntity gameEntity);
    }
#

FGames - 拥有Fragment的所有实现

    public class FGames extends Fragment implements GamesView {

        @BindView(R.id.rv_games)
        RecyclerView rvGames;
        private GamesAdapter gamesAdapter;
        private GamesPresenterImpl presenter;
        OnGameSelectedListener mListener;
        @Nullable
        @Override
        public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
            View view = inflater.inflate(R.layout.games_layout, container, false);
            ButterKnife.bind(this, view);
            presenter = new GamesPresenterImpl(this);
            return view;
        }

        @Override
        public void onAttach(Context context) {
            super.onAttach(context);
            try {
                mListener = (OnGameSelectedListener) context;
            } catch (ClassCastException e) {
                throw new ClassCastException(context.toString() + " must implement OnArticleSelectedListener");
            }
        }

        @Override
        public void onActivityCreated(@Nullable Bundle savedInstanceState) {
            super.onActivityCreated(savedInstanceState);
            presenter.initUi();
        }

        @Override
        public void initRecyclerView(List<GameEntity> gameEntities) {
            gamesAdapter = new GamesAdapter(getActivity(), gameEntities);
            rvGames.setAdapter(gamesAdapter);
            rvGames.setLayoutManager(new LinearLayoutManager(getActivity()));
        }

        @Override
        public void showToast(String message) {
            Toast.makeText(getContext(), message, Toast.LENGTH_SHORT).show();
        }

        @Override
        public void onListItemClick(GameEntity gameEntity) {
          //Here is where the NUll pointer exception is
            mListener.onGameSelected(gameEntity);
        }

        public interface OnGameSelectedListener{
            public void onGameSelected(GameEntity gameEntity);
        }
    }

MainActivity - 显示执行游戏选择的操作以在细节片段可用时更新UI。我按照Android文档执行此操作。

public class MainActivity extends AppCompatActivity implements FGames.OnGameSelectedListener {


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //FGames fGames = new FGames();
        //getSupportFragmentManager().beginTransaction().add(R.id.games_container, fGames).commit();
    }

    @Override
    public void onGameSelected(GameEntity gameEntity) {
        FGameDetail gameDetailFrag = (FGameDetail) getSupportFragmentManager()
                .findFragmentById(R.id.fragment_fGameDetail);
        if (gameDetailFrag == null) {
            // DisplayFragment (Fragment B) is not in the layout (handset layout),
        } else {
            // DisplayFragment (Fragment B) is in the layout (tablet layout),
            // so tell the fragment to update
            gameDetailFrag.updateContent(gameEntity);
        }
    }
}

错误日志

Process: com.example.rao.igttest, PID: 21481
                                                                         java.lang.NullPointerException: Attempt to invoke interface method 'void com.example.rao.igttest.Games.View.FGames$OnGameSelectedListener.onGameSelected(com.example.rao.igttest.Games.Entity.GameEntity)' on a null object reference
                                                                             at com.example.rao.igttest.Games.View.FGames.onListItemClick(FGames.java:73)
                                                                             at com.example.rao.igttest.Games.Presenter.GamesPresenterImpl.showGameDetail(GamesPresenterImpl.java:53)
                                                                             at com.example.rao.igttest.Games.View.GamesAdapter$GamesViewHolder.rowClick(GamesAdapter.java:72)
                                                                             at com.example.rao.igttest.Games.View.GamesAdapter$GamesViewHolder_ViewBinding$1.doClick(GamesAdapter$GamesViewHolder_ViewBinding.java:33)
                                                                             at butterknife.internal.DebouncingOnClickListener.onClick(DebouncingOnClickListener.java:22)
                                                                             at android.view.View.performClick(View.java:5637)
                                                                             at android.view.View$PerformClick.run(View.java:22429)
                                                                             at android.os.Handler.handleCallback(Handler.java:751)
                                                                             at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                             at android.os.Looper.loop(Looper.java:154)
                                                                             at android.app.ActivityThread.main(ActivityThread.java:6119)
                                                                             at java.lang.reflect.Method.invoke(Native Method)
                                                                             at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
                                                                             at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)