java - 在 Recyclerview 中使用外部数据库

Question

我尝试午餐外部数据库的recyclerview。所以我准备了 mydatabase.db.zip 并将其放入 assets/database 文件夹中。编写代码后我发现一个错误 NullPointerException。我不知道问题出在哪里。请帮忙

数据模型：

package com.example.myapplication.DataModel;

public class Name {
    public int id;
    public String name;
    public String meaning;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getMeaning() {
        return meaning;
    }

    public void setMeaning(String meaning) {
        this.meaning = meaning;
    }
}

我的数据库.java

package com.example.myapplication;

import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import com.readystatesoftware.sqliteasset.SQLiteAssetHelper;

public class MyDatabase extends SQLiteAssetHelper {

    private static final String DATABASE_NAME = "niniaad.db";
    private static final int DATABASE_VERSION = 1;
    private static final String TBL_NAME="names";
    private static final String COL_ID="id";
    private static final String COL_NAME="name";
    private static final String COL_MEAN="mean";


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

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    }

    public Cursor getData(){
        SQLiteDatabase sqLiteDatabase=this.getReadableDatabase();
        Cursor cursor=sqLiteDatabase.rawQuery("SELECT * FROM "+TBL_NAME,null);
        return cursor;
    }
}

SecondRecycler.java

package com.example.myapplication;

import android.database.Cursor;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.widget.RelativeLayout;
import com.example.myapplication.Adapter.NameAdapter;
import com.example.myapplication.Adapter.StudentAdapter;
import com.example.myapplication.DataModel.Name;
import com.example.myapplication.DataModel.Students;
import java.util.ArrayList;
import java.util.List;

public class SecondRecycler extends AppCompatActivity {

    RecyclerView recyclerView;
    List<Name> nameList;
    MyDatabase myDatabase;

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

        setupviews();
        getDataFromSqlite();
    }

    private void getDataFromSqlite() {
        Cursor cursor= myDatabase.getData();
        for (cursor.moveToFirst(); !cursor.isAfterLast() ; cursor.moveToNext()) {
            Name name=new Name();
            name.setName(cursor.getString(0));
            name.setMeaning(cursor.getString(1));
            nameList.add(name);
        }
        recyclerView.setAdapter(new NameAdapter(SecondRecycler.this,nameList));
    }

    private void setupviews() {
        MyDatabase myDatabase=new MyDatabase(this);
        recyclerView = (RecyclerView) findViewById(R.id.rv_secondrecycler);
        recyclerView.setLayoutManager(new LinearLayoutManager(SecondRecycler.this));
    }
}

适配器

package com.example.myapplication.Adapter;

import android.content.Context;
import android.support.annotation.NonNull;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import com.example.myapplication.DataModel.Name;
import com.example.myapplication.R;
import java.util.List;


public class NameAdapter extends RecyclerView.Adapter<NameAdapter.NameViewHolder> {

    public Context context;
    public List<Name> nameList;

    public NameAdapter(Context context, List<Name> nameList) {
        this.context = context;
        this.nameList = nameList;
    }

    @NonNull
    @Override
    public NameViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i) {
        View view = LayoutInflater.from(context).inflate(R.layout.secondrecycler_row, viewGroup, false);
        return new NameViewHolder(view);
    }

    @Override
    public void onBindViewHolder(@NonNull NameViewHolder nameViewHolder, int position) {
        Name name = nameList.get(position);
        nameViewHolder.txtName.setText(name.getName());
        nameViewHolder.txtMean.setText(name.getMeaning());
    }

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

    public class NameViewHolder extends RecyclerView.ViewHolder {

        TextView txtName, txtMean;

        public NameViewHolder(@NonNull View itemView) {
            super(itemView);
            txtName = (TextView) itemView.findViewById(R.id.txt_name_Secondrecycler);
            txtMean = (TextView) itemView.findViewById(R.id.txt_mean_seconrecycler);
        }
    }
}

activity_second_recycler.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".SecondRecycler">


    <android.support.v7.widget.RecyclerView
        android:id="@+id/rv_secondrecycler"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />
</RelativeLayout>

recycler_row.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_margin="10dp"
    tools:context=".SecondRecycler">

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <TextView
            android:id="@+id/txt_name_Secondrecycler"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:textSize="30sp"
            android:textColor="#000"
            tools:text="name"
            android:textAlignment="center"
            />

        <TextView
            android:layout_below="@id/txt_name_Secondrecycler"
            android:id="@+id/txt_mean_seconrecycler"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:textSize="30sp"
            android:textColor="#FF0000"
            tools:text="mean"
            />

    </RelativeLayout>

</android.support.v7.widget.CardView>

标签： javaandroiddatabaseandroid-recyclerview