查询数据展示案例 菜鸟级别的我

前几天做了一个小测验，其中一个题目没有做完其中的四五小题。自己不会写长代码，只会一点短小的。老师发的拿来写写。

题目：

编写一个从数据库里查询数据展示到listview上的案例运行结果：点击find按钮，会将数据库中添加的数据显示在List View上。如下：

（1）        entity/Person类中：补充完整构造方法

package cn.edu.bzu.datashow.entity;/** * Created by fengj on 2017/5/10. */public class Person {    private int id;    private String name;    private String phone;    //任务：生成构造方法参数 name,phone    public Person(String name, String phone) {        this.name = name;        this.phone = phone;    }    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 getPhone() {        return phone;    }    public void setPhone(String phone) {        this.phone = phone;}

}

（2）        修正db/PersonDBHelper使其没有错误

package cn.edu.bzu.datashow.db;import android.content.Context;import android.database.sqlite.SQLiteDatabase;import android.database.sqlite.SQLiteOpenHelper;/** * Created by fengj on 2017/5/10. *///任务：修正问题public class PersonDBHelper extends SQLiteOpenHelper {    //数据库的名称为person.db ,数据库的版本为1    public PersonDBHelper(Context context) {        super(context,"person.db", null, 1);    }    @Override    public void onCreate(SQLiteDatabase db) {        db.execSQL("create table info(_id integer primary key,name varchar(20),phone varchar(20))");    }    @Override    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {    }}

（3）        完成dao/PersonDao中的getPersons方法

package cn.edu.bzu.datashow.dao;import android.content.ContentValues;import android.content.Context;import android.database.Cursor;import android.database.sqlite.SQLiteDatabase;import java.util.ArrayList;import java.util.List;import cn.edu.bzu.datashow.db.PersonDBHelper;import cn.edu.bzu.datashow.entity.Person;/** * Created by fengj on 2017/5/10. */public class PersonDao {    private PersonDBHelper personDBHelper;    public PersonDao(Context context){        personDBHelper=new PersonDBHelper(context);    }    public void add(Person person){        SQLiteDatabase sqLiteDatabase=personDBHelper.getWritableDatabase();        ContentValues contentValues=new ContentValues();        contentValues.put("name",person.getName());        contentValues.put("phone",person.getPhone());        sqLiteDatabase.insert("info",null,contentValues);    }    public List<Person> getPersons(){        //任务完成查询所有数据的方法        List<Person> persons=new ArrayList<Person>();        SQLiteDatabase sqLiteDatabase=personDBHelper.getWritableDatabase();        Cursor cursor=sqLiteDatabase.query("info",null,null,null,null,null,null);        while(cursor.moveToNext()){           int id= cursor.getInt(cursor.getColumnIndex("_id"));            String name=cursor.getString(cursor.getColumnIndex("name"));            String phone=cursor.getString(cursor.getColumnIndex("phone"));            Person person=new Person(name,phone);            person.setId(id);            persons.add(person);        }        return persons;    }}

（4）        完成MainActivity中的查询数据库中的所有person，显示在列表中

package cn.edu.bzu.datashow;import android.os.Bundle;import android.support.v7.app.AppCompatActivity;import android.view.View;import android.widget.ListView;import java.util.List;import cn.edu.bzu.datashow.adapter.PersonAdapter;import cn.edu.bzu.datashow.dao.PersonDao;import cn.edu.bzu.datashow.entity.Person;public class MainActivity extends AppCompatActivity {    private PersonDao personDao;    private ListView lvPersons;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        lvPersons= (ListView) findViewById(R.id.lvPersons);        personDao=new PersonDao(this);        personDao.add(new Person("张三","13476089006"));        personDao.add(new Person("李四","13476089008"));    }    public void find(View view){        //任务查询数据库中的所有person，显示在列表中        List<Person> persons=personDao.getPersons();        PersonAdapter personAdapter=new PersonAdapter(this,R.layout.item,persons);        lvPersons.setAdapter(personAdapter);    }}

（5）        已有的代码中设计了一处小小的错误

package cn.edu.bzu.datashow.adapter;import android.content.Context;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;import android.widget.ArrayAdapter;import android.widget.TextView;import java.util.List;import cn.edu.bzu.datashow.R;import cn.edu.bzu.datashow.entity.Person;public class PersonAdapter extends ArrayAdapter<Person> {private int resourceId;public PersonAdapter(Context context, int textViewResourceId, List<Person> objects) {super(context, textViewResourceId, objects);resourceId = textViewResourceId;}@Overridepublic View getView(int position, View convertView, ViewGroup parent) {Person person= getItem(position);View view;ViewHolder viewHolder;if (convertView == null) {//任务补充完整view = LayoutInflater.from(getContext()).inflate(resourceId, null);viewHolder = new ViewHolder();viewHolder.tvName = (TextView) view.findViewById(R.id.tvName);viewHolder.tvPhone = (TextView) view.findViewById(R.id.tvPhone);view.setTag(viewHolder);} else {view = convertView;viewHolder = (ViewHolder) view.getTag();}viewHolder.tvName.setText(person.getName());viewHolder.tvPhone.setText(person.getPhone());return view;}class ViewHolder {TextView tvName;TextView tvPhone;}}

运行结果图为：