java - 无法创建 CardView fragment

Question

我不知道我的代码有什么问题。

我的应用程序正在使用抽屉导航。有 4 个不同的 fragment ，其中一个是 cardview fragment ，我之前已将其从 Activity 转换为 fragment 。

cardview fragment 带有红色下划线，表示无法编译的错误。请引用所附图片。

如果我接受 Android Studio 提出的解决方案，它只会解决 CardViewFragment，而其他 3 个 fragment 会出现新问题。

这既是我的主要 Activity ，也是 cardview fragment 。

MainActivity.java

package info.androidhive.materialdesign.activity;

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentTransaction;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Toast;

import info.androidhive.materialdesign.R;

public class MainActivity extends AppCompatActivity implements FragmentDrawer.FragmentDrawerListener {

    private static String TAG = MainActivity.class.getSimpleName();

    private Toolbar mToolbar;
    private FragmentDrawer drawerFragment;

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

        mToolbar = (Toolbar) findViewById(R.id.toolbar);

        setSupportActionBar(mToolbar);
        getSupportActionBar().setDisplayShowHomeEnabled(true);

        drawerFragment = (FragmentDrawer)
                getSupportFragmentManager().findFragmentById(R.id.fragment_navigation_drawer);
        drawerFragment.setUp(R.id.fragment_navigation_drawer, (DrawerLayout) findViewById(R.id.drawer_layout), mToolbar);
        drawerFragment.setDrawerListener(this);

        // display the first navigation drawer view on app launch
        displayView(0);
    }


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

        if(id == R.id.action_search){
            Toast.makeText(getApplicationContext(), "Search action is selected!", Toast.LENGTH_SHORT).show();
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    @Override
    public void onDrawerItemSelected(View view, int position) {
        displayView(position);
    }

    private void displayView(int position) {
        Fragment fragment = null;
        String title = getString(R.string.app_name);
        switch (position) {
            case 0:
                fragment = new HomeFragment();
                title = getString(R.string.title_home);
                break;
            case 1:
                fragment = new FriendsFragment();
                title = getString(R.string.title_friends);
                break;
            case 2:
                fragment = new MessagesFragment();
                title = getString(R.string.title_messages);
                break;
            case 3:
                fragment = new CardViewFragment();
                title = getString(R.string.title_messages);
                break;
            default:
                break;
        }

        if (fragment != null) {
            FragmentManager fragmentManager = getSupportFragmentManager();
            FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
            fragmentTransaction.replace(R.id.container_body, fragment);
            fragmentTransaction.commit();

            // set the toolbar title
            getSupportActionBar().setTitle(title);
        }
    }
}

CardViewFragment.java

package info.androidhive.materialdesign.activity;

import android.app.Activity;
import android.app.Fragment;
import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.support.v7.app.ActionBarActivity;
import android.support.v7.widget.CardView;
import android.support.v7.widget.GridLayoutManager;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.StaggeredGridLayoutManager;
import android.support.v7.widget.Toolbar;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.LinearLayout;

import java.util.ArrayList;

import info.androidhive.materialdesign.R;


public class CardViewFragment extends Fragment {

    private Toolbar toolbar;
    private RecyclerView recyclerView;
    private CardView cardView;

    private ArrayList<FeddProperties> os_versions;

    private RecyclerView.Adapter mAdapter;
    // private RecyclerView.LayoutManager mLayoutManager;


    private LinearLayout llLayout;
    private FragmentActivity faActivity;
    @Override
    /*protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        initContrls();
    }*/
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState){
        faActivity=(FragmentActivity)
                super.getActivity();
        llLayout=(LinearLayout)
                inflater.inflate(R.layout.activity_main, container, false);

        initContrls();

        return llLayout;
    }

    private void initContrls() {

        //toolbar = (Toolbar) findViewById(R.id.toolbar);
        //  cardView = (CardView) findViewById(R.id.cardList);
        recyclerView = (RecyclerView) llLayout.findViewById(R.id.my_recycler_view);

        /*if (toolbar != null) {
            setSupportActionBar(toolbar);
            getSupportActionBar().setTitle("Android Versions");

        }*/

        final String[] versions = {"Alpha", "Beta", "CupCake", "Donut",
                "Eclair", "Froyo", "Gingerbread", "Honeycomb",
                "Ice Cream Sandwitch", "JellyBean", "KitKat", "LollyPop"};
        final int[] icons = {R.drawable.ic_launcher, R.drawable.ic_launcher, R.drawable.ic_launcher, R.drawable.donut, R.drawable.eclair, R.drawable.froyo, R.drawable.gingerbread, R.drawable.honeycomb, R.drawable.icecream_sandwhich, R.drawable.jellybean, R.drawable.kitkat, R.drawable.lollipop};


        os_versions = new ArrayList<FeddProperties>();

        for (int i = 0; i < versions.length; i++) {
            FeddProperties feed = new FeddProperties();

            feed.setTitle(versions[i]);
            feed.setThumbnail(icons[i]);
            os_versions.add(feed);
        }

        recyclerView.setHasFixedSize(true);

        // ListView
        recyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));

        //Grid View
        // recyclerView.setLayoutManager(new GridLayoutManager(this,2,1,false));

        //StaggeredGridView
        // recyclerView.setLayoutManager(new StaggeredGridLayoutManager(2,1));

        // create an Object for Adapter
        mAdapter = new CardViewDataAdapter(os_versions);

        // set the adapter object to the Recyclerview
        recyclerView.setAdapter(mAdapter);


    }


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

Answer 1

在 MainActivity.java 中，你声明了

import android.support.v4.app.Fragment

在CardViewFragment.java中导入相同类型的Fragment而不是

 import android.app.Fragment;

因此很明显，在两段代码中使用了相同类型的 fragment 。