SQLite、Cursor简单使用

本文完成数据库创建，查询，增加，删除操作。理论就不这么说了，就是那几步，先看效果:



添加权限

SD读写权限：android.permission.WRITE_EXTERNAL_STORAGE

继承SQLiteOpenHelper

/**
* @project DBDemo
* @ClassName DBOpenHelper.java
* @Description 这里表名是写死的，实际使用中不要这样
* @author xugang
* @date 2015-12-21 下午1:18:12
*/
public class DBOpenHelper extends SQLiteOpenHelper {

private final static String dbName = "mydb.db";
public final static String tableName = "student";
// 数据库版本
private static final int VERSION = 1;
//建学生表，主键自增长
String sql = "Create Table " + tableName + "(userId INTEGER Primary Key AUTOINCREMENT,userName varchar(32),age int(32),time varchar(32))";

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

public DBOpenHelper(Context context, String name, int version) {
this(context, name, null, version);
}

public DBOpenHelper(Context context) {
this(context, dbName, VERSION);
}

@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL(sql);
}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
//数据库更新,简单点可以直接删除表
//但是推荐将旧表数据导入到新表后再删除
}
}

获取SQLiteDatabase，进行增删改查操作

package com.example.dbdemo;

import java.util.Random;

import com.example.dbdemo.db.core.DBOpenHelper;

import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.Button;
import android.widget.ListView;
import android.app.Activity;
import android.content.ContentValues;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;

public class MainActivity extends Activity implements OnClickListener, OnItemClickListener {

private DBOpenHelper dbOpenHelper;
//操作数据库
private SQLiteDatabase db;
private Button btnAdd;
private Button btnSelect;
private Button btnDel;
private ListView lv;
private MyAdapter myAdapter;

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

private void init() {
btnAdd = (Button) findViewById(R.id.btnAdd);
btnDel = (Button) findViewById(R.id.btnDel);
btnSelect = (Button) findViewById(R.id.btnSelect);
lv = (ListView) findViewById(R.id.lv);

btnDel.setEnabled(false);

btnAdd.setOnClickListener(this);
btnSelect.setOnClickListener(this);
btnDel.setOnClickListener(this);
lv.setOnItemClickListener(this);

dbOpenHelper = new DBOpenHelper(this);
db = dbOpenHelper.getWritableDatabase();
}

private int[] ages = { 12, 18, 21, 43, 12, 43, 65, 67 };
private String[] names = { "Jack", "Tom", "Linar", "Bann", "Ajax", "Rain", "Sun" };
private Student student;
private Cursor cursor = null;

@Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.btnAdd:
//增加一条数据到表中
ContentValues contentValues = new ContentValues();
contentValues.put("userName", names[new Random().nextInt(7)]);
contentValues.put("age", ages[new Random().nextInt(8)]);
contentValues.put("time", String.valueOf(System.currentTimeMillis()));
db.insertOrThrow(DBOpenHelper.tableName, null, contentValues);
break;
case R.id.btnSelect:
//查询表，展现在Adapter中
cursor = db.rawQuery("select * from student", null);
myAdapter = new MyAdapter(this, cursor);
lv.setAdapter(myAdapter);

break;

case R.id.btnDel:
//删除一条数据
if (student != null) {
db.delete(DBOpenHelper.tableName, " time = ?", new String[] { student.getTime() });
btnDel.setEnabled(false);
}
break;

default:
break;
}
}

@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
btnDel.setEnabled(true);
student = (Student) parent.getItemAtPosition(position);
}
}

Adapter

package com.example.dbdemo;

import android.content.Context;
import android.database.Cursor;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.TextView;

/**
* @project DBDemo
* @ClassName MyAdapter.java
* @Description 填充ListView Adapter
* @author xugang
* @date 2015-12-21 下午4:14:00
*/
public class MyAdapter extends BaseAdapter {

private Cursor cursor;
private LayoutInflater inflater;

public MyAdapter(Context context, Cursor cursor) {
inflater = LayoutInflater.from(context);
this.cursor = cursor;
}

@Override
public int getCount() {
return cursor.getCount();
}

@Override
public Object getItem(int position) {
if (cursor.moveToPosition(position)) {
Student student = new Student(cursor.getString(cursor.getColumnIndexOrThrow("userName")), cursor.getInt(cursor.getColumnIndexOrThrow("age")), cursor.getString(cursor.getColumnIndexOrThrow("time")));
return student;
}
return null;
}

@Override
public long getItemId(int position) {
return position;
}

@Override
public View getView(int position, View view, ViewGroup parent) {
ViewHolder holder;
if (view == null) {
holder = new ViewHolder();
view = inflater.inflate(R.layout.item, parent, false);
holder.tvTime = (TextView) view.findViewById(R.id.tvTime);
holder.tvUserAge = (TextView) view.findViewById(R.id.tvUserAge);
holder.tvUserName = (TextView) view.findViewById(R.id.tvUserName);
view.setTag(holder);
} else {
holder = (ViewHolder) view.getTag();
}
Student student = (Student) getItem(position);
if (student != null) {
holder.tvUserName.setText("用户名:" + student.getUserName());
holder.tvUserAge.setText("年龄:" + student.getAge());
holder.tvTime.setText("添加时间:" + student.getTime());
}
return view;
}

private class ViewHolder {
TextView tvUserName;
TextView tvUserAge;
TextView tvTime;
}

}

实体类Student

package com.example.dbdemo;

/**
* @project DBDemo
* @ClassName Student.java
* @Description 实体类
* @author xugang
* @date 2015-12-21 下午2:55:06
*/
public class Student {

private String userName;
private int age;
private String time;

public String getUserName() {
return userName;
}

public void setUserName(String userName) {
this.userName = userName;
}

public int getAge() {
return age;
}

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

public String getTime() {
return time;
}

public void setTime(String time) {
this.time = time;
}

@Override
public String toString() {
return "Student [userName=" + userName + ", age=" + age + ", time=" + time + "]";
}

public Student() {
super();
}

public Student(String userName, int age, String time) {
super();
this.userName = userName;
this.age = age;
this.time = time;
}

}

这里的增加和删除数据都要再次查询才可以刷新，在Android 3.0引入了Loaders机制，就不用这么麻烦了，这个下次在研究吧。