无法将上下文转换为片段的 FragmentAdapter 中的 CustomCallBack 接口

Question

我在 Fragment 的 FragmentAdapter 中投射上下文时遇到问题。我的应用程序流程是： - 当我点击导航列表项 (Nav One) 时，它将显示带有 recyclerview 和 cardview 的片段。 - 当我单击 cardview 列表项的图像时，我想要一个操作来显示 Toast 消息或使用名为 (CustomCallBack) 的自定义接口执行某些操作。这是我的代码：

MainActivity.java

public class MainActivity extends AppCompatActivity {

    private Toolbar toolbar;
    private ListView lvNavigation;
    private DrawerLayout mDrawer;
    private NavigationView mNavigation;
    private LinearLayout llMianContain;
    String[] navigation = new String[]{"Nav One","Nav Two", "Nav Three","Nav Four"};
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        toolbar = (Toolbar) findViewById(R.id.toolbar);
        lvNavigation = (ListView) findViewById(R.id.lv_listView);
        mDrawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        mNavigation= (NavigationView) findViewById(R.id.navigation_view);
        llMianContain = (LinearLayout) findViewById(R.id.ll_main_content);

        setSupportActionBar(toolbar);
        lvNavigation.setAdapter(new ArrayAdapter<>(this, android.R.layout.simple_list_item_1, navigation));
        lvNavigation.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
                replaceFragment(i);
                lvNavigation.setItemChecked(i, true);
                hideDrawer();
            }
        });

        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(this, mDrawer, toolbar, R.string.open, R.string.close);
        mDrawer.setDrawerListener(toggle);
        toggle.syncState();
    }
    private void replaceFragment(int position){
        Fragment fragment = null;
        switch (position){
            case 0:
                fragment = new OneFragment();
                break;
            case 1:
                fragment = new TwoFragment();
                break;
            case 2:
                fragment = new ThreeFragment();
                break;
            case 3:
                fragment= new FourFragment();
                break;
            default:
                fragment = new OneFragment();
                break;
        }
        if(null!= fragment){
            FragmentManager manager = getSupportFragmentManager();
            FragmentTransaction transaction = manager.beginTransaction();
            transaction.replace(R.id.ll_main_content, fragment);
            transaction.addToBackStack(null);
            transaction.commit();
        }
    }
    private void hideDrawer(){
        mDrawer.closeDrawer(GravityCompat.START);
    }
    private void showDrawer(){
        mDrawer.openDrawer(GravityCompat.START);
    }
    @Override
    public void onBackPressed() {
        if (mDrawer.isDrawerOpen(GravityCompat.START))
            hideDrawer();
        else
            super.onBackPressed();
    }
}

OneFragment.java

public class OneFragment extends Fragment implements FragmentOneAdapter.CustomCallBack{

    private ArrayList<ListItem> listItems;
    private RecyclerView recyclerView;
    private FragmentOneAdapter adapter;

    public OneFragment() { }
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View view =inflater.inflate(R.layout.fragment_one, container, false);
        recyclerView = (RecyclerView) view.findViewById(R.id.recycler_view);
        LinearLayoutManager manager = new LinearLayoutManager(getActivity());
        recyclerView.setLayoutManager(manager);
        listItems = new ArrayList<>();
        for(int i=0;i<40;i++){
            listItems.add(new ListItem(R.drawable.ic_account_circle_black_48dp, "MY NAME "+ i));
        }
        adapter = new FragmentOneAdapter(listItems, getActivity());
        recyclerView.setAdapter(adapter);
        return view;
    }

    @Override
    public void onProfileClick(int position) {
        Toast.makeText(getActivity(), "position "+ position, Toast.LENGTH_SHORT).show();
    }
}

FragmentAdapter.java

public class FragmentOneAdapter extends RecyclerView.Adapter<FragmentOneAdapter.FragmentOneViewHolder> {

    private ArrayList<ListItem> listItems;
    private Context context;
    final CustomCallBack customCallBack;

    public FragmentOneAdapter(ArrayList<ListItem> listItems, Context context){
        this.listItems = listItems;
        this.context = context;
        this.customCallBack = (CustomCallBack) context;
    }
    @Override
    public FragmentOneViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.fragment_one_item, parent,false);
        FragmentOneViewHolder holder = new FragmentOneViewHolder(view);

        return holder;
    }
    @Override
    public void onBindViewHolder(FragmentOneViewHolder holder, int position) {
        holder.tvName.setText(listItems.get(position).getName());
        holder.ivProfile.setImageResource(listItems.get(position).getProfile());
    }
    @Override
    public int getItemCount() {
        return listItems.size();
    }
    class FragmentOneViewHolder extends RecyclerView.ViewHolder{
        TextView tvName;
        ImageView ivProfile;
        LinearLayout llFooter;

        public FragmentOneViewHolder(View itemView) {
            super(itemView);
            tvName = (TextView) itemView.findViewById(R.id.tv_name);
            ivProfile = (ImageView) itemView.findViewById(R.id.iv_profile);
            llFooter= (LinearLayout) itemView.findViewById(R.id.ll_footer);

            ivProfile.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View view) {
                    customCallBack.onProfileClick(getAdapterPosition());
                }
            });
        }
    }

//    MY Custom CallBack
    interface CustomCallBack{
        void onProfileClick(int position);
    }
}

Answer 1

嗯，

所以你的 Fragment 正在实现 CustomCallBack 接口

为什么不直接将 Fragment 对象本身传递给适配器？

例如，在 FragmentOneAdapter.java、

变化：

public FragmentOneAdapter(ArrayList<ListItem> listItems, Context context) ===> public FragmentOneAdapter(ArrayList<ListItem> listItems, CustomCallBack callback)

然后：

this.customCallBack = (CustomCallBack) context; ===> this.customCallBack = callback;

显然，现在 OneFragment.java，

只需将 'this' 作为参数传递，因为 Fragment 本身就是 CustomCallBack:

adapter = new FragmentOneAdapter(listItems, getActivity()); ===> adapter = new FragmentOneAdapter(listItems, this);

无法将上下文转换为片段的 FragmentAdapter 中的 CustomCallBack 接口

Can't cast context to CustomCallBack interface in FragmentAdapter of a Fragment

java

android

fragment

android-fragments

android-cardview