片段中的Recyclerview不会立即显示警报对话框结果

Question

在我的项目中，我有一个主要活动，其中包含3个片段，这些片段在启动时通过TabPage中的ViewPager显示。在我的一个片段中，我有一个RecyclerView和一个FAB，单击它们时会启动一个警报对话框，该对话框捕获要在片段中的RV中显示的用户输入。在对话框中单击“添加”后，RV中什么也没有出现，但是当我单击FAB并重试时，它出现在RV中。因此，我要说的是，我必须在FAB中输入两次信息，然后信息才能在我的RV片段中显示。所以我想知道是否有人可以帮助我理解为什么会这样。好像我的RV中的RV没有立即创建，但所有应用程序均未崩溃，因此没有日志可发布。我已经研究过，但无济于事。我是自学成才，因此将不胜感激。

片段

public class SubjectsFrag extends DialogFragment implements CardAdapter.ClickListener,
        SubjectsEditor.OnAddSubjectListener
{
    private static final String TAG = SubjectsFrag.class.getSimpleName();

    @NonNull
    Context context;
    private EditText titleView, teacherView;
    private String sTitle, sTeacher;
    public EmptyRecyclerView recyclerView;
    public RecyclerView.LayoutManager layoutManager;
    public CardAdapter cardAdapter;
    public SubjectsModel model = null;
    public ArrayList<SubjectsModel> subMod = new ArrayList<>();
    DbHelper dbHelper;
    @BindView(R.id.main_root)
    ViewGroup root;

    public SubjectsFrag() {
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {

        View view = inflater.inflate(R.layout.fragment_subjects, container, false);

        FloatingActionButton fab = view.findViewById(R.id.fab_sub);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                showDialog();
            }
        });

        titleView = view.findViewById(R.id.edit_subject);
        teacherView = view.findViewById(R.id.edit_subject_teacher);

        View emptyView = view.findViewById(R.id.empty_subject_view);

        recyclerView = view.findViewById(R.id.recycler_view);
        recyclerView.setHasFixedSize(true);


        cardAdapter = new CardAdapter(getContext(), subMod);

        layoutManager = new LinearLayoutManager(getActivity());
        recyclerView.setLayoutManager(layoutManager);
        recyclerView.setAdapter(cardAdapter);

        return view;
    }

    @Override
    public void itemClicked(View view, int position) {

    }

    @Override
    public void OnAddSubjectSubmit(String title, String teacher)
    {
        SubjectsModel model = new SubjectsModel(sTitle, sTeacher);

        model.setmTitle(title);
        model.setmTeacher(teacher);
        subMod.add(model);

        cardAdapter.notifyDataSetChanged();

    }

    private void showDialog()
    {
        SubjectsEditor addSubjectDialog = new SubjectsEditor();
        addSubjectDialog.setTargetFragment(this, 0);
        addSubjectDialog.show(getFragmentManager(), null);

    }
}

对话框片段

public class SubjectsEditor extends DialogFragment
{
    Context context;
    private OnAddSubjectListener listener;
    @BindView(R.id.main_root)
    ViewGroup root;

    public interface OnAddSubjectListener
    {
        void OnAddSubjectSubmit(String title, String teacher);
    }

    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        try{
            listener = (OnAddSubjectListener) getTargetFragment();
        } catch (ClassCastException e) {
            throw new ClassCastException("Calling fragment must implement onAddSubjectListener");
        }
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        return inflater.inflate(R.layout.editor_subjects, container, false);
    }

    public Dialog onCreateDialog(Bundle savedInstanceState)
    {
        View view = LayoutInflater.from(getActivity()).inflate(R.layout.editor_subjects, root);
        final EditText mTitle = view.findViewById(R.id.edit_subject);
        final EditText mTeacher = view.findViewById(R.id.edit_subject_teacher);
        AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
        builder.setView(view)
                .setTitle("Add Subject")
                .setPositiveButton("Add", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        final String sTitle = mTitle.getText().toString();
                        final String sTeacher = mTeacher.getText().toString();

                        listener.OnAddSubjectSubmit(sTitle, sTeacher);
                    }
                })
                .setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        dialog.dismiss();
                    }
                });
        return builder.create();
    }
}

回收站适配器

public class CardAdapter extends RecyclerView.Adapter<CardAdapter.CardViewHolder>
{
    public ArrayList<SubjectsModel> subMod;
    private OnItemClicked onClick;
    static ClickListener clickListener;
    Context context;

    public CardAdapter(Context context, ArrayList<SubjectsModel> items)
    {
        this.context = context;
        this.subMod = items;
    }

    @NonNull
    @Override
    public CardAdapter.CardViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType)
    {
        return new CardViewHolder(LayoutInflater.from(context).inflate(R.layout.subjects_item_list,
                parent, false));
    }

    @Override
    public void onBindViewHolder(final CardAdapter.CardViewHolder holder, final int position)
    {
       SubjectsModel currentSubject = subMod.get(position);

        holder.titleView.setText(currentSubject.getmTitle());
        holder.teacher.setText(currentSubject.getmTeacher());
    }

    public class CardViewHolder extends RecyclerView.ViewHolder implements
            View.OnClickListener
    {
        TextView titleView;
        TextView teacher;
        CardView cardView;

        public CardViewHolder(View itemView)
        {
            super(itemView);
            titleView = itemView.findViewById(R.id.subject_subject);
            teacher = itemView.findViewById(R.id.subject_teacher_text);
            cardView = itemView.findViewById(R.id.card_view);

            cardView.setOnClickListener(this);

        }

        @Override
        public void onClick(View view)
        {
            if (clickListener != null)
            {
                clickListener.itemClicked(view, getAdapterPosition());
                Toast.makeText(context, R.string.hello_blank_fragment, Toast.LENGTH_SHORT).show();
            }
        }
    }

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

    public interface OnItemClicked
    {
        void onItemClick(int position);
    }

    public void setOnClick(OnItemClicked onClick)
    {
        this.onClick = onClick;
    }

    public void setClickListener(ClickListener clicked)
    {
        CardAdapter.clickListener = clicked;
    }

    public interface ClickListener
    {
        public void itemClicked(View view, int position);
    }
}

片段xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/main_root">


    <com.example.ashleighwilson.schoolscheduler.adapter.EmptyRecyclerView
        android:id="@+id/recycler_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_marginTop="60dp"/>

   <RelativeLayout
       android:layout_width="wrap_content"
       android:layout_height="wrap_content"
       android:layout_centerInParent="true">

    <TextView
        android:id="@+id/empty_subject_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:gravity="center"
        android:visibility="gone"
        android:text="@string/no_subjects"/>

   </RelativeLayout>

    <android.support.design.widget.FloatingActionButton
        android:id="@+id/fab_sub"
        style="@style/FAB" />

</RelativeLayout>

主要活动

public class OverviewActivity extends AppCompatActivity
{

    private NavigationView mNavigationView;
    private DrawerLayout drawer;
    private ActionBarDrawerToggle toggle;
    CharSequence tabTitles[] = {"SUBJECTS", "TASKS", "CALENDER"};
    int numOfTabs = 3;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main_nav);

        Toolbar toolbar = findViewById(R.id.main_toolbar);
        setSupportActionBar(toolbar);

        final ViewPager viewPager = findViewById(R.id.viewpager);

        ViewPagerAdapter adapter = new ViewPagerAdapter(this, getSupportFragmentManager(), tabTitles, numOfTabs);
        viewPager.setAdapter(adapter);

        TabLayout tabLayout = findViewById(R.id.tabs);
        tabLayout.setupWithViewPager(viewPager);

        drawer = findViewById(R.id.drawer_layout);
        toggle = new ActionBarDrawerToggle(
                    this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
        toggle.syncState();

        mNavigationView = findViewById(R.id.nav_view);
        setupDrawerContent(mNavigationView);

       /* FloatingActionButton fab = findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
            }
        }); */

        viewPager.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(tabLayout));
        tabLayout.addOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
            @Override
            public void onTabSelected(TabLayout.Tab tab)
            {
                viewPager.setCurrentItem(tab.getPosition());
            }

            @Override
            public void onTabUnselected(TabLayout.Tab tab) {

            }

            @Override
            public void onTabReselected(TabLayout.Tab tab) {

            }
        });
    }

    @Override
    public void onBackPressed()
    {
        //DrawerLayout drawer = findViewById(R.id.drawer_layout);
        if (drawer.isDrawerOpen(GravityCompat.START))
        {
            drawer.closeDrawer(GravityCompat.START);
        }
        else
            super.onBackPressed();
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main_nav, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    private void setupDrawerContent(NavigationView navigationView)
    {
        navigationView.setNavigationItemSelectedListener(new NavigationView.OnNavigationItemSelectedListener() {
            @Override
            public boolean onNavigationItemSelected(@NonNull MenuItem menuItem)
            {
                selectDrawerItem(menuItem);
                return true;
            }
        });
    }

    public void selectDrawerItem(MenuItem menuItem)
    {
        switch (menuItem.getItemId())
        {
            case R.id.nav_grades:
                Intent gradesIntent = new Intent(this, GradesActivity.class);
                startActivity(gradesIntent);
                break;
            case R.id.nav_notes:
                Intent notesIntent = new Intent(this, NotesActivity.class);
                startActivity(notesIntent);
                break;
        }

        menuItem.setChecked(true);
        setTitle(menuItem.getTitle());
        drawer.closeDrawer(GravityCompat.START);
    }

}

Answer 1

一次性进行一次，没有任何动作。您可以使用调试器或Log.d(String, String)调用来挑战关于何时调用的假设。当您调用适配器的notifyDataSetChanged()，然后在适配器本身内部的getItemCount和bind或createViewHolder调用时，我会仔细研究一下。

Answer 2

使用notifyDataSetChanged()应该可以解决问题。选中此answer