如何在片段中使用cardView [android -java]实现回收器视图

Question

在线上有很多教程。但是，我尝试了很多，但它们都无法做到我的期望正确。

我是Android和App开发的新手，但是有一些开发网站和API的经验。我已经开发了一个网站，并想创建一个简单的Android应用程序，以显示为用户的活动提要。

因此，经过一番研究，似乎可以处理来自API的JSON数据列表的最佳方法是RecyClerview，并且CardViews将提高设计。

因此，我设置了一个带有底部磁带的项目，并创建了三个选项卡(事件，配置文件和通知(。这些标签返回片段，列表应在事件片段中。我已经对其进行了硬编码以显示5个项目，但它从未显示出卡片。因此，我不确定它在哪里错。其他片段正确显示

这是我的代码：

basefragment

public abstract class BaseFragment extends AppCompatActivity {
    protected abstract Fragment createFragment();
    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_user);
        FragmentManager fm = getSupportFragmentManager();
        Fragment fragment = fm.findFragmentById(R.id.content);
        if(fragment == null){
            fragment = createFragment();
            fm.beginTransaction()
                    .add(R.id.events_fragment_container, fragment)
                    .commit();
        }

    }
}

事件片段，适配器和View holder

public class EventsRecyclerFragment extends Fragment{
    public static Fragment newInstance(){
        return new EventsRecyclerFragment();
    }
    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.events_recycler_view_fragment, container, false);
        RecyclerView recyclerView = view.findViewById(R.id.events_recycler_view);
        recyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));
        recyclerView.setAdapter(new EventsRecyclerViewAdapter());
        return view;
    }
    private class EventsRecyclerViewHolder extends RecyclerView.ViewHolder{
        private CardView mCardView;
        private TextView mTextView;
        public EventsRecyclerViewHolder(View itemView) {
            super(itemView);
        }
        public EventsRecyclerViewHolder(LayoutInflater inflater, ViewGroup container){
            super(inflater.inflate(R.layout.events_card_view, container, false));
            mCardView = itemView.findViewById(R.id.events_card_container);
        }
    }
    private class EventsRecyclerViewAdapter extends  RecyclerView.Adapter<EventsRecyclerViewHolder>{
        @Override
        public EventsRecyclerViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
            LayoutInflater inflater = LayoutInflater.from(getContext());
            return new EventsRecyclerViewHolder(inflater, parent);
        }
        @Override
        public void onBindViewHolder(EventsRecyclerViewHolder holder, int position) {
        }
        @Override
        public int getItemCount() {
            return 5;
        }
    }
}

我在活动上的使用

public class UserActivity extends AppCompatActivity {
    public static final String PREFS_NAME = "Preferences";
    private static final String PREF_EMAIL = "EMAIL";
    private static final String PREF_PASSWORD = "PASSWORD";
    private static final String PREF_TOKEN = "TOKEN";
    Button btnLogout;
    private BottomNavigationView.OnNavigationItemSelectedListener mOnNavigationItemSelectedListener
            = new BottomNavigationView.OnNavigationItemSelectedListener() {
        @Override
        public boolean onNavigationItemSelected(@NonNull MenuItem item) {
            FragmentManager manager = getSupportFragmentManager();
            FragmentTransaction transaction = manager.beginTransaction();

            switch (item.getItemId()) {
                case R.id.navigation_events:
                    transaction.replace(R.id.content, new EventsRecyclerFragment().newInstance()).commit();
                    return true;
                case R.id.navigation_profile:
                    transaction.replace(R.id.content, new UserFragment()).commit();
                    return true;
                case R.id.navigation_notifications:
                    transaction.replace(R.id.content, new NotificationsFragment()).commit();
                    return true;
            }
            return false;
        }
    };
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_user);
        btnLogout = (Button) findViewById(R.id.btnLogin);
        BottomNavigationView navigation = (BottomNavigationView) findViewById(R.id.navigation);
        navigation.setOnNavigationItemSelectedListener(mOnNavigationItemSelectedListener);
    }
}

谁能帮助我如何使这个基本列表显示？预先感谢

Answer 1

需要两个更改：

1. UserActivity：在newInstance()方法返回新实例本身时，从EventsRecyclerFragment()实例初始化删除new关键字。

   public class UserActivity extends AppCompatActivity {
     public static final String PREFS_NAME = "Preferences";
     private static final String PREF_EMAIL = "EMAIL";
     private static final String PREF_PASSWORD = "PASSWORD";
     private static final String PREF_TOKEN = "TOKEN";
     Button btnLogout;
     private BottomNavigationView.OnNavigationItemSelectedListener mOnNavigationItemSelectedListener
         = new BottomNavigationView.OnNavigationItemSelectedListener() {
       @Override
       public boolean onNavigationItemSelected(@NonNull MenuItem item) {
         FragmentManager manager = getSupportFragmentManager();
         FragmentTransaction transaction = manager.beginTransaction();
   
         switch (item.getItemId()) {
    case R.id.navigation_events:
                   transaction.replace(R.id.content, EventsRecyclerFragment().newInstance()).commit();
                   return true;
               case R.id.navigation_profile:
                   transaction.replace(R.id.content, new UserFragment()).commit();
                   return true;
               case R.id.navigation_notifications:
                   transaction.replace(R.id.content, new NotificationsFragment()).commit();
                   return true;
         }
         return false;
       }
     };
     @Override
     protected void onCreate(Bundle savedInstanceState) {
       super.onCreate(savedInstanceState);
       setContentView(R.layout.activity_main);
       BottomNavigationView navigation =  findViewById(R.id.navigation);
       navigation.setOnNavigationItemSelectedListener(mOnNavigationItemSelectedListener);
     }
   }
   

2. events recyclerFragment：在其初始化期间始终设置回收室视图的orientation。

    public class EventsRecyclerFragment extends Fragment{
           public static Fragment newInstance(){
               return new EventsRecyclerFragment();
           }
           @Nullable
           @Override
           public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
               View view = inflater.inflate(R.layout.events_recycler_view_fragment, container, false);
               RecyclerView recyclerView = view.findViewById(R.id.events_recycler_view);
               LinearLayoutManager linearLayoutManager =new LinearLayoutManager(getActivity());
         linearLayoutManager.setOrientation(LinearLayoutManager.VERTICAL);
               recyclerView.setLayoutManager(linearLayoutManager);
               recyclerView.setAdapter(new EventsRecyclerViewAdapter());
               return view;
           }
           private class EventsRecyclerViewHolder extends RecyclerView.ViewHolder{
               private CardView mCardView;
               private TextView mTextView;
               public EventsRecyclerViewHolder(View itemView) {
                   super(itemView);
               }
               public EventsRecyclerViewHolder(LayoutInflater inflater, ViewGroup container){
                   super(inflater.inflate(R.layout.events_card_view, container, false));
                   mCardView = itemView.findViewById(R.id.events_card_container);
               }
           }
           private class EventsRecyclerViewAdapter extends  RecyclerView.Adapter<EventsRecyclerViewHolder>{
               @Override
               public EventsRecyclerViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
                   LayoutInflater inflater = LayoutInflater.from(getContext());
                   return new EventsRecyclerViewHolder(inflater, parent);
               }
               @Override
               public void onBindViewHolder(EventsRecyclerViewHolder holder, int position) {
               }
               @Override
               public int getItemCount() {
                   return 5;
               }
           }
       }