java - viewPager 上的 RecyclerView 崩溃

Question

起初，我的 recyclerview 在没有 ViewPager 的情况下从头开始顺利运行。但是，当我尝试在 ViewPager 适配器上添加 recyclerview 时，它崩溃了，并显示错误位于 getAllData() 的数据库帮助程序中。提前TY。希望有人能帮我解决这个问题。

这是我的代码。

FragmentMeal.java

package inncharge.poy.madrigal.innchargev1.fragments;


import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v7.widget.DefaultItemAnimator;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import inncharge.poy.madrigal.innchargev1.R;
import inncharge.poy.madrigal.innchargev1.activities.DatabaseHelper;
import inncharge.poy.madrigal.innchargev1.adapters.DataBeanAdapter;
import inncharge.poy.madrigal.innchargev1.pojo.DataBean;


/**
 * A simple {@link Fragment} subclass.
 * Use the {@link FragmentMeal#newInstance} factory method to
 * create an instance of this fragment.
 */
public class FragmentMeal extends Fragment {



    // TODO: Rename parameter arguments, choose names that match
    // the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
    private static final String ARG_PARAM1 = "param1";
    private static final String ARG_PARAM2 = "param2";

    // TODO: Rename and change types of parameters
    private String mParam1;
    private String mParam2;
    DatabaseHelper helper = new DatabaseHelper(getActivity());
    private RecyclerView mRecyclerView;


    /**
     * Use this factory method to create a new instance of
     * this fragment using the provided parameters.
     *
     * @param param1 Parameter 1.
     * @param param2 Parameter 2.
     * @return A new instance of fragment FragmentMeal.
     */
    // TODO: Rename and change types and number of parameters
    public static android.support.v4.app.Fragment newInstance(String param1, String param2) {
        FragmentMeal fragment = new FragmentMeal();
        Bundle args = new Bundle();
        args.putString(ARG_PARAM1, param1);
        args.putString(ARG_PARAM2, param2);
        fragment.setArguments(args);
        return fragment;
    }

    public FragmentMeal() {
        // Required empty public constructor
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if (getArguments() != null) {
            mParam1 = getArguments().getString(ARG_PARAM1);
            mParam2 = getArguments().getString(ARG_PARAM2);
        }

    }


    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        View view = inflater.inflate(R.layout.fragment_meal, container, false);
        mRecyclerView = (RecyclerView) view.findViewById(R.id.recycler_view);
        mRecyclerView.setHasFixedSize(true);
        mRecyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));
        mRecyclerView.setItemAnimator(new DefaultItemAnimator());
        mRecyclerView.setAdapter(new DataBeanAdapter(helper.getAllData(), R.layout.item));
        return view;
    }



}

DatabaseHelper.java

    package inncharge.poy.madrigal.innchargev1.activities;

    import android.content.ContentValues;
    import android.content.Context;
    import android.database.Cursor;
    import android.database.sqlite.SQLiteDatabase;
    import android.database.sqlite.SQLiteOpenHelper;

    import java.util.ArrayList;
    import java.util.List;

    import inncharge.poy.madrigal.innchargev1.pojo.DataBean;

    /**
     * Created by Madrigal on 8/9/2015.
     */
    public class DatabaseHelper extends SQLiteOpenHelper {

        private  static final int DATABASE_VERSION = 1;
        private  static final String DATABASE_NAME = "contacts.db";
        private  static final String TABLE_NAME = "contacts";
        private  static final String UID = "id";
        private  static final String NAME = "name";
        private  static final String CARD = "card";
        private  static final String CODE = "code";
        SQLiteDatabase db;
        private static final String TABLE_CREATE = "CREATE TABLE contacts (id INTEGER PRIMARY KEY NOT NULL," +
                "name TEXT NOT NULL , card TEXT NOT NULL, code TEXT NOT NULL)";

        public DatabaseHelper(Context context) {
            super(context, DATABASE_NAME, null, DATABASE_VERSION);

        }

        @Override
        public void onCreate(SQLiteDatabase db) {
            db.execSQL(TABLE_CREATE);
            this.db = db;
        }

        public void insertBean(DataBean bean) {

            db = this.getWritableDatabase();
            ContentValues values = new ContentValues();

            String query = "SELECT * FROM contacts";
            Cursor cursor = db.rawQuery(query, null);
            int count = cursor.getCount();

            values.put(UID, count);
            values.put(NAME, bean.getName());
            values.put(CARD, bean.getCard());
            values.put(CODE, bean.getCode());

            db.insert(TABLE_NAME, null, values);
            db.close();

        }

        public List<DataBean> getAllData() {
            db = this.getWritableDatabase();
            String query = "SELECT * FROM contacts";
            Cursor cursor = db.rawQuery(query, null);

            List<DataBean> list = new ArrayList<>();

            while (cursor.moveToNext()) {
                int index = cursor.getColumnIndex(UID);
                int index2 = cursor.getColumnIndex(NAME);
                int index3 = cursor.getColumnIndex(CARD);
                int index4 = cursor.getColumnIndex(CODE);
                int id = cursor.getInt(index);
                String name = cursor.getString(index2);
                String card = cursor.getString(index3);
                String code = cursor.getString(index4);
                DataBean bean = new DataBean();
                bean.setId(id);
                bean.setName(name);
                bean.setCard(card);
                bean.setCode(code);
                list.add(bean);
            }
            return list;
        }


    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        String query = "DROP TABLE IF EXIST"+TABLE_NAME;
        db.execSQL(query);
        this.onCreate(db);
    }
}

ViewPager适配器

private class ViewPagerAdapter extends FragmentStatePagerAdapter {

        int icons[] = {R.drawable.ic_action_meal,
                R.drawable.ic_action_drinks,
                R.drawable.ic_action_snack};

        public ViewPagerAdapter(FragmentManager fm) {
            super(fm);
        }

        public Fragment getItem(int num) {

            Fragment fragment = null;

            switch (num) {
                case MEAL:
                    fragment = FragmentMeal.newInstance("", "");
                    break;
                case DRINKS:
                    fragment = FragmentDrinks.newInstance("", "");
                    break;
                case SNACK:
                    fragment = FragmentSnack.newInstance("", "");
                    break;
            }
                return fragment;
        }

        @Override
        public int getCount() {

            return 3;
        }

        @Override
        public CharSequence getPageTitle(int position) {
            return getResources().getStringArray(R.array.tabs)[position];
        }

        private Drawable getIcon(int position) {

            return ResourcesCompat.getDrawable(getResources(), icons[position], null);

        }

    }

适配器

package inncharge.poy.madrigal.innchargev1.adapters;

import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import java.util.List;

import inncharge.poy.madrigal.innchargev1.R;
import inncharge.poy.madrigal.innchargev1.pojo.DataBean;

/**
 * Created by Madrigal on 8/17/2015.
 */
public class DataBeanAdapter extends RecyclerView.Adapter<DataBeanAdapter.ViewHolder>{
    private List<DataBean> items;
    private int itemLayout;

    public DataBeanAdapter(List<DataBean> items, int itemLayout){
        this.items = items;
        this.itemLayout = itemLayout;
    }

    @Override
    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View v = LayoutInflater.from(parent.getContext()).inflate(itemLayout, parent, false);
        return new ViewHolder(v);
    }

    @Override
    public void onBindViewHolder(ViewHolder holder, int position) {
        DataBean item = items.get(position);
        holder.name.setText(item.getName());
        holder.card.setText(item.getCard());
        //All the thing you gonna show in the item
    }

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

    public static class ViewHolder extends RecyclerView.ViewHolder {
        public TextView name;
        public TextView card;

        public ViewHolder(View itemView) {
            super(itemView);
            name = (TextView) itemView.findViewById(R.id.name);
            card = (TextView) itemView.findViewById(R.id.card);
        }
    }
}

从操作评论中编辑添加的 logcat

08-17 17:17:26.299 1333-1333/? E/AndroidRuntime﹕ FATAL EXCEPTION: main java.lang.NullPointerException at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java‌​:224) at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.ja‌​va:164) at inncharge.poy.madrigal.innchargev1.activities.DatabaseHelper.getAllData(Database‌​Helper.java:61) at inncharge.poy.madrigal.innchargev1.fragments.FragmentMeal.onCreateView(FragmentM‌​eal.java:82)

java:82 error is this. mRecyclerView.setAdapter(new DataBeanAdapter(helper.getAllData(), R.layout.item));

lang java:61 erro is this. public List getAllData() { db = this.getWritableDatabase();

请注意:
当我在没有 viewpager 的情况下尝试回收器 View 时，它工作得很好，但是当我尝试将其添加到我的 View 寻呼机时。出现此错误。

Answer 1

movetonext是将光标移动到下一行，isafterlast会判断是否有下一行。另外，将光标移动到第一个条目。

http://developer.android.com/reference/android/database/Cursor.html

并尝试获取列索引处的值作为列索引。

更改您的列表和适配器，如下所示。

在你的 oncreate 中。

List items = helper.getAllData();
ArrayAdapter adapter = new ArrayAdapter(getActivity(), R.layout.item,
            R.id.textList, items);

在你的助手类中。

public List getAllData()
    List list = new ArrayList();

更改 while 循环，如下所示。

cursor.moveToFirst();

while (!cursor.isAfterLast()) {
  //  int index = cursor.getColumnIndex(UID);
  //  int index2 = cursor.getColumnIndex(NAME);
  //  int index3 = cursor.getColumnIndex(CARD);
  //  int index4 = cursor.getColumnIndex(CODE);
    int id = cursor.getInt(0);
    String name = cursor.getString(1);
    String card = cursor.getString(2);
    String code = cursor.getString(3);
    DataBean bean = new DataBean();
    bean.setId(id);
    bean.setName(name);
    bean.setCard(card);
    bean.setCode(code);
    list.add(bean);
    cursor.moveToNext();
}

我还建议在循环中分解您的实现，模块化，就目前而言，其中发生了很多事情。

反馈后进行编辑:

我看不到您在哪里使用ViewPagerAdapter。这可能是您的空指针异常。

我建议你看看这里:
http://developer.android.com/reference/android/support/v4/app/FragmentStatePagerAdapter.html .

如果这没有帮助，请回复我。