利用SQLiteOpenHelper创建数据库，进行增删改查操作

Android中提供SQLiteOpenHelper类，在该类的构造器中，调用Context中的方法创建并打开一个指定名称的数据库对象。继承和扩展SQLiteOpenHelper类主要做的工作就是重写以下两个方法。onCreate(SQLiteDatabase db) : 当数据库被首次创建时执行该方法，一般将创建表等初始化操作在该方法中执行。 
onUpgrade(SQLiteDatabse dv, int oldVersion,int new Version)：当打开数据库时传入的版本号与当前的版本号不同时会调用该方法进行更新。
 首先建立一个名为MyDbHelper的类继承SQLiteOpenHelper，目的是为了创建数据库。
我们要用到三个类，

MyDbHelper(创建数据库)    UserDao（操作的方法）     User(数据)

一个Activity

代码如下：

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

/**
 * Created by Administrator on 2016/8/22.
 */
public class MyDbHelper extends SQLiteOpenHelper {
private final String TABLENAME="info";        //创建表名为info的数据库
    private final String INFO_COLUM_ID="_id";     //依次为表中的数据，其中“_id”表示id为主键
    private final String INFO_COLUM_NAME="name";  //其次为name,pwd,age,img
    private final String INFO_COLUM_PWD="pwd";
    private final String INFO_COLUM_AGE="age";
    private final String INFO_COLUM_IMG="img";

    public MyDbHelper(Context context){

        super(context,"user.db",null,1); //user.db表示数据库名 1表示版本号，以后如果修改代码后，改版本号进行更新

    }
    public MyDbHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {
        super(context, name, factory, version);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
          StringBuilder sql=new StringBuilder();
          sql.append(" Create table if not exists ");
          sql.append(TABLENAME+"(");
          sql.append(INFO_COLUM_ID+" integer primary key autoincrement,");   //integer primary key autoincrement表示主键

          sql.append(INFO_COLUM_NAME+" varchar(10),");                        //varchar表示长度
          sql.append(INFO_COLUM_PWD+" varchar(10),");
          sql.append(INFO_COLUM_AGE+" varchar(10),");
          sql.append(INFO_COLUM_IMG+" varchar(10)");
          sql.append(")");
          db.execSQL(sql.toString());
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        String sql=" drop table if exist"+TABLENAME;                         //更新时调用
        db.execSQL(sql);
        onCreate(db);

    }
}

UserDao类中写增删改查的方法

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;

/**
 * Created by Administrator on 2016/8/22.
 */
public class UserDao {
    private MyDbHelper myDbHelper;
    public UserDao(Context context){
        myDbHelper=new MyDbHelper(context);
    }
    //插入数据
    public void insert(User user){
        SQLiteDatabase db=myDbHelper.getWritableDatabase();
        ContentValues cv=new ContentValues();
        cv.put("name",user.getName());
        cv.put("pwd",user.getPwd());
        cv.put("age",user.getAge());
        cv.put("img",user.getImg());
        db.insert("info", null, cv);

        db.close();
    }
    //删除所有数据
    public void delete(){
        SQLiteDatabase db=myDbHelper.getWritableDatabase();
        db.delete("info", null, null);
        db.close();
    }
    //删除一条数据
    public void deleteUser(String id){
        SQLiteDatabase db=myDbHelper.getWritableDatabase();
        db.delete("info","_id=?",new String []{id});
        db.close();
    }
    //查询一条数据
    public User searchUser(String id){
        SQLiteDatabase db=myDbHelper.getReadableDatabase();
        Cursor cs= db.query("info", null, "_id = ?", new String[]{id}, null, null, null);
        User user=null;
        if(cs.moveToNext()){
            user=new User();
            user.setUserId(cs.getInt(cs.getColumnIndex("_id")));
            user.setName(cs.getString(cs.getColumnIndex("name")));
            user.setPwd(cs.getString(cs.getColumnIndex("pwd")));
            user.setAge(cs.getString(cs.getColumnIndex("age")));
            user.setImg(cs.getString(cs.getColumnIndex("img")));
        }
        cs.close();
        db.close();
        return user;
    }
    //查询所有数据
    public List search(){
        SQLiteDatabase db=myDbHelper.getReadableDatabase();
        Cursor cs=db.query("info", null, null, null, null, null, null);
        User user=null;
        List<User> list=new ArrayList<>();
        while (cs.moveToNext()){
            user=new User();
            user.setUserId(cs.getInt(cs.getColumnIndex("_id")));
            user.setName(cs.getString(cs.getColumnIndex("name")));
            user.setPwd(cs.getString(cs.getColumnIndex("pwd")));
            user.setAge(cs.getString(cs.getColumnIndex("age")));
            user.setImg(cs.getString(cs.getColumnIndex("img")));
            list.add(user);
        }
        cs.close();
        db.close();
        return list;
    }
    //修改数据
    public void update(User user){
        SQLiteDatabase db=myDbHelper.getWritableDatabase();
        ContentValues cv=new ContentValues();
        cv.put("name",user.getName());
        cv.put("pwd", user.getPwd());
        cv.put("age", user.getAge());
       // cv.put("img",user.getImg());

        String id=String.valueOf(user.getUserId());
        db.update("info",cv,"_id=? ",new String[]{id});
        db.close();
    }

user类

public class User {
    private int userId;
    private String name;
    private String pwd;
    private String age;
    private String img;

    public int getUserId() {
        return userId;
    }

    public void setUserId(int userId) {
        this.userId = userId;
    }

    public String getName() {
        return name;
    }

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

    public String getPwd() {
        return pwd;
    }

    public void setPwd(String pwd) {
        this.pwd = pwd;
    }

    public String getAge() {
        return age;
    }

    public void setAge(String age) {
        this.age = age;
    }

    public String getImg() {
        return img;
    }

    public void setImg(String img) {
        this.img = img;
    }

    @Override
    public String toString() {
        return "User{" +
                "userId=" + userId +
                ", name='" + name + '\'' +
                ", pwd='" + pwd + '\'' +
                ", age='" + age + '\'' +
                ", img='" + img + '\'' +
                '}';
    }
}

}

Activity中的代码如下

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Spinner;
import android.widget.TextView;
import android.widget.Toast;

import com.example.administrator.ch02.entity.User;
import com.example.administrator.ch02.entity.UserDao;

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

public class MainActivity extends AppCompatActivity {
    private EditText name,age,pwd;           //布局中的EditView
    private Button inster,search,delete,update;  //布局中的Button
    private TextView show;                       //用于显示数据
    private UserDao userDao;                     //dao类
    private Spinner spinner;                     //布局中的Spinner
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        name= (EditText) findViewById(R.id.name);
        age= (EditText) findViewById(R.id.age);
        pwd= (EditText) findViewById(R.id.pwd);
        inster= (Button) findViewById(R.id.inster1);
        search= (Button) findViewById(R.id.search);
        spinner= (Spinner) findViewById(R.id.spinner);
        delete= (Button) findViewById(R.id.delete);
        update= (Button) findViewById(R.id.update);
        userDao=new UserDao(this);
        inster.setOnClickListener(new View.OnClickListener() { //增加数据
            @Override
            public void onClick(View v) {
                User user=new User();
                user.setName(name.getText().toString());
                user.setAge(age.getText().toString());
                user.setPwd(pwd.getText().toString());
                userDao.insert(user);
                Toast.makeText(getBaseContext(), "新增成功", Toast.LENGTH_SHORT).show();

            }
        });
        search.setOnClickListener(new View.OnClickListener() {      //查询数据
            @Override
            public void onClick(View v) {
                List<User> list=userDao.search();
               // show.setText(list.toString());
                List myDate=new ArrayList();
                for(User u:list){
                    myDate.add(u.getUserId()+":"+u.getName());
                }
                ArrayAdapter aa=new ArrayAdapter(getBaseContext(),android.R.layout.simple_list_item_1,myDate);
                spinner.setAdapter(aa);
             }
        });
        spinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {    //spinner点击事件
            @Override
            public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
                String str = spinner.getSelectedItem().toString();
                if (!str.equals("")) {
                    String id1 = str.split(":")[0];
                    User user = userDao.searchUser(id1);
                    name.setText(user.getName().toString());
                    age.setText(user.getAge().toString());
                    pwd.setText(user.getPwd().toString());
                }
            }

            @Override
            public void onNothingSelected(AdapterView<?> parent) {

            }
        });
        delete.setOnClickListener(new View.OnClickListener() {     //删除数据
            @Override
            public void onClick(View v) {
                String str = spinner.getSelectedItem().toString();
                if (!str.equals("")) {
                    String id = str.split(":")[0];
                    userDao.deleteUser(id);
                }

            }
        });
        update.setOnClickListener(new View.OnClickListener() {     //修改数据
            @Override
            public void onClick(View v) {
                String str = spinner.getSelectedItem().toString();
                if (!str.equals("")) {
                    String id = str.split(":")[0];
                    User user=userDao.searchUser(id);
                        user.setName(name.getText().toString());
                        user.setPwd(pwd.getText().toString());
                        user.setAge(age.getText().toString());
                        userDao.update(user);
                }
            }
        });
    }
}