项目上的RecyclerView单击NullPointerException

Question

所以我用SQLite DB设置了我的RecyclerView并填充了列表，但是每次点击列表项时，它都应该打开新活动并通过intent extras将数据传递给它。

点击给我Process: com.daroioradecic.fxtodo, PID: 6762 java.lang.NullPointerException: Attempt to invoke interface method 'void data.RecAdapter$ItemClickCallback.onItemClick(int)' on a null object reference at data.RecAdapter$RecHolder.onClick(RecAdapter.java:106) at android.view.View.performClick(View.java:4856) at android.view.View$PerformClick.run(View.java:19956) at android.os.Handler.handleCallback(Handler.java:739) at android.os.Handler.dispatchMessage(Handler.java:95) at android.os.Looper.loop(Looper.java:211) at android.app.ActivityThread.main(ActivityThread.java:5389) at java.lang.reflect.Method.invoke(Native Method) at java.lang.reflect.Method.invoke(Method.java:372) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1020) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:815)

public class RecAdapter extends RecyclerView.Adapter<RecAdapter.RecHolder> {

    private int previousPosition = 0;

    private List<Todo> listData;
    private LayoutInflater inflater;

    private ItemClickCallback itemClickCallback;


    public interface ItemClickCallback {
        void onItemClick(int p);
    }


    public void setItemClickCallback(final ItemClickCallback itemClickCallback) {
        this.itemClickCallback = itemClickCallback;
    }


    public RecAdapter(List<Todo> listData, Context c) {
        this.inflater = LayoutInflater.from(c);
        this.listData = listData;
    }


    @Override
    public RecHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view = inflater.inflate(R.layout.layout_row_za_listu, parent, false);
        return new RecHolder(view);
    }

    @Override
    public void onBindViewHolder(RecHolder holder, int position) {
        Todo item = listData.get(position);
        holder.title.setText(item.getTitle());

        if (position > previousPosition) {
            AnimationUtil.animate(holder, true);
        } else {
            AnimationUtil.animate(holder, false);
        }
        previousPosition = position;

    }

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


    public void setListData(ArrayList<Todo> exerciseList) {
        this.listData.clear();
        this.listData.addAll(exerciseList);
    }


    class RecHolder extends RecyclerView.ViewHolder implements View.OnClickListener {
        private TextView title;
        private View container;

        public RecHolder(View itemView) {
            super(itemView);
            title = (TextView) itemView.findViewById(R.id.tekstNaListi);
            container = itemView.findViewById(R.id.cont_item_root);
            container.setOnClickListener(this);
        }

        @Override
        public void onClick(View v) {
            itemClickCallback.onItemClick(getAdapterPosition());

        }
    }


}

在我的Recycler View适配器类中：

itemClickCallback.onItemClick(getAdapterPosition());

它在行 @Override public void onItemClick(int p) { Todo item = (Todo) listData.get(p); Intent i = new Intent(HomeScreen.this, Details.class); Bundle extras = new Bundle(); extras.putString("naslov", item.getTitle()); extras.putString("datum", item.getRecordDate()); extras.putInt("id", item.getItemId()); startActivity(i); } 上给出错误，这是该类中的最后一行。

我在这个填充了回收站视图的类中重写onClick：

implements RecAdapter.ItemClickCallback

该类实现public class HomeScreen extends AppCompatActivity implements RecAdapter.ItemClickCallback { private RecyclerViewUtils.ShowHideToolbarOnScrollingListener showHideToolbarListener; //SCROLL private Toolbar tToolbar; // REC private RecyclerView recView; private RecAdapter adapter; private ArrayList listData; // ZA SNACKBAR private CoordinatorLayout coordinatorLayout; private RelativeLayout relLay; // NAVIGACIJA private DrawerLayout mDrawer; private ActionBarDrawerToggle drawerToggle; private Toolbar toolbar; NavigationView nvDrawer; DrawerLayout dlDrawer; //---------------------------------------------------------------------------------------------- DatabaseHandler dba; private ArrayList<Todo> dbTodo = new ArrayList<>(); private TodoAdapter todoAdapter; private ListView lista; private Cursor mCursor; LinearLayout layoutZaUnosTodoa; EditText editTextZaNazivTodoa; Button buttonSave; private CheckBox checkBoxDoneOrNotNaListi; android.support.design.widget.FloatingActionButton fab; @TargetApi(Build.VERSION_CODES.LOLLIPOP) @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); //getWindow().requestFeature(Window.FEATURE_ACTION_BAR_OVERLAY); setContentView(R.layout.activity_home_screen); tToolbar = (Toolbar) findViewById(R.id.tToolbar); setSupportActionBar(tToolbar); tToolbar.setNavigationIcon(R.drawable.ic_nav_menu); getSupportActionBar().setTitle(R.string.app_name); // REC recView = (RecyclerView) findViewById(R.id.rec_list); recView.setLayoutManager(new LinearLayoutManager(this)); adapter = new RecAdapter(listData, this); recView.setAdapter(adapter); adapter.setItemClickCallback(this); recView.addOnScrollListener(showHideToolbarListener = new RecyclerViewUtils.ShowHideToolbarOnScrollingListener(tToolbar)); if (savedInstanceState != null) { showHideToolbarListener.onRestoreInstanceState((RecyclerViewUtils.ShowHideToolbarOnScrollingListener.State) savedInstanceState .getParcelable(RecyclerViewUtils.ShowHideToolbarOnScrollingListener.SHOW_HIDE_TOOLBAR_LISTENER_STATE)); } layoutZaUnosTodoa = (LinearLayout) findViewById(R.id.layoutZaUnosTodoa); editTextZaNazivTodoa = (EditText) findViewById(R.id.editTextZaNazivTodoa); editTextZaNazivTodoa.setSelection(editTextZaNazivTodoa.getText().length()); buttonSave = (Button) findViewById(R.id.buttonSave); //lista = (ListView) findViewById(R.id.lista); fab = (android.support.design.widget.FloatingActionButton) findViewById(R.id.fab); checkBoxDoneOrNotNaListi = (CheckBox) findViewById(R.id.checkBoxDoneOrNotNaListi); coordinatorLayout = (CoordinatorLayout) findViewById(R.id.coordiantorLayout); relLay = (RelativeLayout) findViewById(R.id.relLay); refreshData(); layoutZaUnosTodoa.setVisibility(View.GONE); fab.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { layoutZaUnosTodoa.setVisibility(View.VISIBLE); } }); buttonSave.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { saveToDB(); layoutZaUnosTodoa.setVisibility(View.GONE); } }); relLay.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { layoutZaUnosTodoa.setVisibility(View.GONE); } }); dlDrawer = (DrawerLayout) findViewById(R.id.drawer_layout); drawerToggle = setupDrawerToggle(); dlDrawer.setDrawerListener((DrawerLayout.DrawerListener) drawerToggle); mDrawer = (DrawerLayout) findViewById(R.id.drawer_layout); nvDrawer = (NavigationView) findViewById(R.id.nvView); setupDrawerContent(nvDrawer); drawerToggle.syncState(); } @Override public void onSaveInstanceState(Bundle outState) { outState.putParcelable(RecyclerViewUtils.ShowHideToolbarOnScrollingListener.SHOW_HIDE_TOOLBAR_LISTENER_STATE, showHideToolbarListener.onSaveInstanceState()); super.onSaveInstanceState(outState); } private void saveToDB() { Todo todo = new Todo(); todo.setTitle(editTextZaNazivTodoa.getText().toString()); dba.addTodo(todo); adapter.notifyDataSetChanged(); dba.close(); editTextZaNazivTodoa.setText(""); } public void refreshData() { dbTodo.clear(); dba = new DatabaseHandler(HomeScreen.this); ArrayList<Todo> todoFromDB = dba.getTodo(); for (int i = 0; i < todoFromDB.size(); i++) { String title = todoFromDB.get(i).getTitle(); String dateText = todoFromDB.get(i).getRecordDate(); int mid = todoFromDB.get(i).getItemId(); Todo myTodo = new Todo(); myTodo.setTitle(title); myTodo.setItemId(mid); myTodo.setRecordDate(dateText); dbTodo.add(myTodo); } dba.close(); adapter = new RecAdapter(dbTodo, this); recView.setAdapter(adapter); // todoAdapter = new TodoAdapter(HomeScreen.this, R.layout.layout_row_za_listu, dbTodo); //Animation collapseList = AnimationUtils.loadAnimation(HomeScreen.this, R.anim.collapse_search_results); //lista.startAnimation(collapseList); //lista.setAdapter(todoAdapter); // todoAdapter.notifyDataSetChanged(); } @Override public void onItemClick(int p) { Todo item = (Todo) listData.get(p); Intent i = new Intent(HomeScreen.this, Details.class); Bundle extras = new Bundle(); extras.putString("naslov", item.getTitle()); extras.putString("datum", item.getRecordDate()); extras.putInt("id", item.getItemId()); startActivity(i); } /* @Override public void onSecondaryItemClick(int p) { }*/ public class TodoAdapter extends ArrayAdapter<Todo> { Activity activity; int layoutResource; Todo todo; ArrayList<Todo> mData = new ArrayList<>(); public TodoAdapter(Activity act, int resource, ArrayList<Todo> data) { super(act, resource, data); activity = act; layoutResource = resource; mData = data; notifyDataSetChanged(); } @Override public int getCount() { return mData.size(); } @Override public Todo getItem(int position) { return mData.get(position); } @Override public int getPosition(Todo item) { return super.getPosition(item); } @Override public long getItemId(int position) { return super.getItemId(position); } @Override public View getView(int position, View convertView, ViewGroup parent) { View row = convertView; ViewHolder holder = null; if (row == null || (row.getTag() == null)) { LayoutInflater inflater = LayoutInflater.from(activity); row = inflater.inflate(layoutResource, null); holder = new ViewHolder(); holder.mTitle = (TextView) row.findViewById(R.id.tekstNaListi); holder.checkBox = (CheckBox) row.findViewById(R.id.checkBoxDoneOrNotNaListi); row.setTag(holder); } else { holder = (ViewHolder) row.getTag(); } holder.myTodo = getItem(position); holder.mTitle.setText(holder.myTodo.getTitle()); final ViewHolder finalHolder = holder; holder.mTitle.setOnLongClickListener(new View.OnLongClickListener() { @Override public boolean onLongClick(View v) { int mid = finalHolder.myTodo.getItemId(); DatabaseHandler dba = new DatabaseHandler(HomeScreen.this); dba.deleteTodo(mid); Snackbar snackbar = Snackbar.make(coordinatorLayout, getResources().getString(R.string.snack_bar_tekst), Snackbar.LENGTH_SHORT); snackbar.show(); todoAdapter.notifyDataSetChanged(); return true; } }); /*holder.mTitle.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { String title = finalHolder.myTodo.getTitle().toString(); String dateText = finalHolder.myTodo.getRecordDate().toString(); int mid = finalHolder.myTodo.getItemId(); Intent i = new Intent(HomeScreen.this, Details.class); i.putExtra("naslov", title); i.putExtra("datum", dateText); i.putExtra("id", mid); startActivity(i); } });*/ final View finalRow = row; holder.checkBox.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { finalHolder.mTitle = (TextView) finalRow.findViewById(R.id.tekstNaListi); if (finalHolder.checkBox.isChecked()) { finalHolder.mTitle.setPaintFlags(finalHolder.mTitle.getPaintFlags() | Paint.STRIKE_THRU_TEXT_FLAG); finalHolder.mTitle.setAlpha(0.5f); } else if (!finalHolder.checkBox.isChecked()) { finalHolder.mTitle.setPaintFlags(0); finalHolder.mTitle.setAlpha(0.8f); } } }); return row; } } class ViewHolder { Todo myTodo; TextView mTitle, mContent, mDate; int mId; CheckBox checkBox; }

有什么想法吗？谢谢！

主要活动类:(请记住，我刚刚从ListView过渡到所以我还没有完成任何清洁工作）

java.lang.NullPointerException: Attempt to invoke interface method 'void data.RecAdapter$ItemClickCallback.onItemClick(int)' on a null object reference
                                                                            at data.RecAdapter$1.onClick(RecAdapter.java:67)

编辑：

此错误显示：

itemClickCallback.onItemClick(position);

并且它在适配器类中提到了这一行：

require 'addressable/uri'

Answer 1

1）检查回调是否为空。

animal = new Cow();// you cant do it
animal.color="white";// you can do it

2）activity / class实现该方法。这没关系。但是，您是否在@Override public void onClick(View v) { if (itemClickCallback!=null){ itemClickCallback.onItemClick(getAdapterPosition()); } } ？

中设置了听众

onCreate()

3）已编辑更改适配器，如下所示：

rectAdapter.setItemClickCallback(this);