关于数据库SQLite的学习与理解

学习Android买了本书是欧阳燊的《Android stduio 开发实战 从零基础到App上线》，而数据库这个问题困扰我好长时间了。

昨天，去作者的博客下了整本书的源码，终于有些顿悟了。

作者博客：http://my.csdn.net/aqi00

个人觉得讲的还不错的：http://blog.csdn.net/qq_22797039/article/details/51902754

个人觉得讲的也很好的：http://bbs.sunofbeaches.com/thread-5783-1-2.html

有关SQLite的视频：http://bbs.sunofbeaches.com/thread-4622-1-1.html

关于数据库SQLite我觉得主要有两部分，一部分是写数据库的代码，另一部分是在你的那个Activity.java上使用第一部分的数据库代码。

！！！代码的注释是个人理解！！！本人学生一个，还在进步中~~~

代码共有四个类：

                             一个是你的那个Activity.java类,如我的就是SQLWriteActivity类（用来实现数据库的代码）

                             一个数据库类，如我的数据库类就是UserDBHelper类（主要是创建数据库和写数据库的增删查改的代码）

                             一个临时存放数据的的类，就如同将我的SQLiteWriteActivity的数据运送到UserDBHelper的中转站，我的这个类名是UserInfo类

                             一个关于时间日期的自定义类，这个类主要是想在界面上显示一下存放数据的时间日期，写不写没多大的关系，我的这个类名是DateUtil类

                             UserInfo这个类会在UserDBHelper类中用到，SQLWriteActivity类中也有，这四个类的代码都会在下面给出。

第一部分的数据库代码（UserDBHelper类）：

import java.util.ArrayList;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;
//继承SQLiteOpenHelper
public class UserDBHelper extends SQLiteOpenHelper {
    private static final String TAG = "UserDBHelper";
    //数据库名称
    private static final String DB_NAME = "user.db";
    //数据库版本
    private static final int DB_VERSION = 1;
    //UserDBHelper的实例对象
    private static UserDBHelper mHelper = null;
    private SQLiteDatabase mDB = null;
    private static final String TABLE_NAME = "user_info";
    //只传入一个上下文（默认为this）的参数的构造参数
    private UserDBHelper(Context context) {
        super(context, DB_NAME, null, DB_VERSION);
    }
    //传入上下文与版本号的构造参数
    private UserDBHelper(Context context, int version) {
        super(context, DB_NAME, null, version);
    }
    //获取UserDBHelper的实例对象，传入上下文与版本号的参数，用来判断数据库的状态。
    public static UserDBHelper getInstance(Context context, int version) {
        if (version > 0 && mHelper == null) {
            mHelper = new UserDBHelper(context, version);
        } else if (mHelper == null) {
            mHelper = new UserDBHelper(context);
        }
        return mHelper;
    }
    //实现读取数据库的操作
    public SQLiteDatabase openReadLink() {
        if (mDB == null || mDB.isOpen() != true) {
            mDB = mHelper.getReadableDatabase();
        }
        return mDB;
    }
    //实现写入数据库的操作
    public SQLiteDatabase openWriteLink() {
        if (mDB == null || mDB.isOpen() != true) {
            mDB = mHelper.getWritableDatabase();
        }
        return mDB;
    }
    //关闭数据库
    public void closeLink() {
        if (mDB != null && mDB.isOpen() == true) {
            mDB.close();
            mDB = null;
        }
    }
    //获取数据库的名称
    public String getDBName() {
        if (mHelper != null) {
            return mHelper.getDatabaseName();
        } else {
            return DB_NAME;
        }
    }
    //首次调用时，会进行
    @Override
    public void onCreate(SQLiteDatabase db) {
        Log.d(TAG, "onCreate");
        String drop_sql = "DROP TABLE IF EXISTS " + TABLE_NAME + ";";
        Log.d(TAG, "drop_sql:" + drop_sql);
        db.execSQL(drop_sql);
        String create_sql = "CREATE TABLE IF NOT EXISTS " + TABLE_NAME + " ("
                + "_id INTEGER PRIMARY KEY  AUTOINCREMENT NOT NULL,"
                + "name VARCHAR NOT NULL," + "age INTEGER NOT NULL,"
                + "height LONG NOT NULL," + "weight FLOAT NOT NULL,"
                + "married INTEGER NOT NULL," + "update_time VARCHAR NOT NULL"
                //演示数据库升级时要先把下面这行注释
                + ",phone VARCHAR" + ",password VARCHAR"
                + ");";
        Log.d(TAG, "create_sql:" + create_sql);
        db.execSQL(create_sql);
    }
    //数据库版本号更新时会调用
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        Log.d(TAG, "onUpgrade oldVersion="+oldVersion+", newVersion="+newVersion);
        if (newVersion > 1) {
            //Android的ALTER命令不支持一次添加多列，只能分多次添加
            String alter_sql = "ALTER TABLE " + TABLE_NAME + " ADD COLUMN " + "phone VARCHAR;";
            Log.d(TAG, "alter_sql:" + alter_sql);
            db.execSQL(alter_sql);
            alter_sql = "ALTER TABLE " + TABLE_NAME + " ADD COLUMN " + "password VARCHAR;";
            Log.d(TAG, "alter_sql:" + alter_sql);
            db.execSQL(alter_sql);
        }
    }
    //删除condition这一行的数据
    public int delete(String condition) {
        int count = mDB.delete(TABLE_NAME, condition, null);
        return count;
    }
    //删除全部的数据
    public int deleteAll() {
        int count = mDB.delete(TABLE_NAME, "1=1", null);
        return count;
    }
    //添加数据，其中的UserInfo类是一个自定义的类
    public long insert(UserInfo info) {
        ArrayList infoArray = new ArrayList();
        infoArray.add(info);
        return insert(infoArray);
    }
    //该方法由上面的那个insert方法调用，是添加数据的主力军！
    public long insert(ArrayList infoArray) {
        long result = -1;
        for (int i = 0; i < infoArray.size(); i++) {
            UserInfo info = infoArray.get(i);
            ArrayList tempArray = new ArrayList();
            // 如果存在同名记录，则更新记录
            // 注意条件语句的等号后面要用单引号括起来
            if (info.name!=null && info.name.length()>0) {
                String condition = String.format("name='%s'", info.name);
                tempArray = query(condition);
                if (tempArray.size() > 0) {
                    update(info, condition);
                    result = tempArray.get(0).rowid;
                    continue;
                }
            }
            // 如果存在同样的手机号码，则更新记录
            if (info.phone!=null && info.phone.length()>0) {
                String condition = String.format("phone='%s'", info.phone);
                tempArray = query(condition);
                if (tempArray.size() > 0) {
                    update(info, condition);
                    result = tempArray.get(0).rowid;
                    continue;
                }
            }
            // 不存在唯一性重复的记录，则插入新记录
            ContentValues cv = new ContentValues();
            cv.put("name", info.name);
            cv.put("age", info.age);
            cv.put("height", info.height);
            cv.put("weight", info.weight);
            cv.put("married", info.married);
            cv.put("update_time", info.update_time);
            cv.put("phone", info.phone);
            cv.put("password", info.password);
            result = mDB.insert(TABLE_NAME, "", cv);
            // 添加成功后返回行号，失败后返回-1
            if (result == -1) {
                return result;
            }
        }
        return result;
    }
    //将参数info中的数据录入数据库
    public int update(UserInfo info, String condition) {
        ContentValues cv = new ContentValues();
        cv.put("name", info.name);
        cv.put("age", info.age);
        cv.put("height", info.height);
        cv.put("weight", info.weight);
        cv.put("married", info.married);
        cv.put("update_time", info.update_time);
        cv.put("phone", info.phone);
        cv.put("password", info.password);
        int count = mDB.update(TABLE_NAME, cv, condition, null);
        return count;
    }

    public int update(UserInfo info) {
        return update(info, "rowid="+info.rowid);
    }
    //查询方法，将数据放入infoArray上，返回infoArray
    public ArrayList query(String condition) {
        String sql = String.format("select rowid,_id,name,age,height,weight,married,update_time," +
                "phone,password from %s where %s;", TABLE_NAME, condition);
        Log.d(TAG, "query sql: "+sql);
        ArrayList infoArray = new ArrayList();
        Cursor cursor = mDB.rawQuery(sql, null);
        if (cursor.moveToFirst()) {
            for (;; cursor.moveToNext()) {
                UserInfo info = new UserInfo();
                info.rowid = cursor.getLong(0);
                info.xuhao = cursor.getInt(1);
                info.name = cursor.getString(2);
                info.age = cursor.getInt(3);
                info.height = cursor.getLong(4);
                info.weight = cursor.getFloat(5);
                //SQLite没有布尔型，用0表示false，用1表示true
                info.married = (cursor.getInt(6)==0)?false:true;
                info.update_time = cursor.getString(7);
                info.phone = cursor.getString(8);
                info.password = cursor.getString(9);
                infoArray.add(info);
                if (cursor.isLast() == true) {
                    break;
                }
            }
        }
        cursor.close();
        return infoArray;
    }

    public UserInfo queryByPhone(String phone) {
        UserInfo info = null;
        ArrayList infoArray = query(String.format("phone='%s'", phone));
        if (infoArray.size() > 0) {
            info = infoArray.get(0);
        }
        return info;
    }

}

第二部分的SQLiteWriteActivity类代码：

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

public class SQLiteWriteActivity extends AppCompatActivity implements OnClickListener {

    private UserDBHelper mHelper;
    private EditText et_name;
    private EditText et_age;
    private EditText et_height;
    private EditText et_weight;
    private boolean bMarried = false;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_sqlite_write);
//      初始化
        et_name = (EditText) findViewById(R.id.et_name);
        et_age = (EditText) findViewById(R.id.et_age);
        et_height = (EditText) findViewById(R.id.et_height);
        et_weight = (EditText) findViewById(R.id.et_weight);
        findViewById(R.id.btn_save).setOnClickListener(this);

        ArrayAdapter typeAdapter = new ArrayAdapter(this,
                R.layout.support_simple_spinner_dropdown_item, typeArray);
        typeAdapter.setDropDownViewResource(R.layout.support_simple_spinner_dropdown_item);
        Spinner sp_married = (Spinner) findViewById(R.id.sp_married);
        sp_married.setPrompt("请选择婚姻状况");
        sp_married.setAdapter(typeAdapter);
        sp_married.setSelection(0);
        sp_married.setOnItemSelectedListener(new TypeSelectedListener());

    }

    private String[] typeArray = {"未婚", "已婚"};



    class TypeSelectedListener implements OnItemSelectedListener {
        public void onItemSelected(AdapterView arg0, View arg1, int arg2, long arg3) {

            bMarried = (arg2==0)?false:true;
        }

        public void onNothingSelected(AdapterView arg0) {
        }
    }
    //在App生命周期的onStart方法中初始化数据库，并打开写入
    @Override
    protected void onStart() {
        super.onStart();
        mHelper = UserDBHelper.getInstance(this, 2);
        mHelper.openWriteLink();
    }

    //在App生命周期的onStop方法中关闭数据库
    @Override
    protected void onStop() {
        super.onStop();
        mHelper.closeLink();
    }

    @Override
    public void onClick(View v) {
        if (v.getId() == R.id.btn_save) {
            String name = et_name.getText().toString();
            String age = et_age.getText().toString();
            String height = et_height.getText().toString();
            String weight = et_weight.getText().toString();
            if (name==null || name.length()<=0) {
                showToast("请先填写姓名");
                return;
            }
            if (age==null || age.length()<=0) {
                showToast("请先填写年龄");
                return;
            }
            if (height==null || height.length()<=0) {
                showToast("请先填写身高");
                return;
            }
            if (weight==null || weight.length()<=0) {
                showToast("请先填写体重");
                return;
            }
            //这里用到了UserInfo类
            UserInfo info = new UserInfo();
            //装车QAQ
            info.name = name;
            info.age = Integer.parseInt(age);
            info.height = Long.parseLong(height);
            info.weight = Float.parseFloat(weight);
            info.married = bMarried;
            //这里用到DateUtil类
            info.update_time = DateUtil.getNowDateTime("yyyy-MM-dd HH:mm:ss");
            //倒车入库
            mHelper.insert(info);
            showToast("数据已写入SQLite数据库");
        }
    }

    private void showToast(String desc) {
        Toast.makeText(this, desc, Toast.LENGTH_SHORT).show();
    }

    
}

DateUtil类：

import android.annotation.SuppressLint;

import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;


public class DateUtil {
    @SuppressLint("SimpleDateFormat")
    public static String getNowDateTime(String formatStr) {
        String format = formatStr;
        if (format==null || format.length()<=0) {
            format = "yyyyMMddHHmmss";
        }
        SimpleDateFormat s_format = new SimpleDateFormat(format);
        return s_format.format(new Date());
    }

    @SuppressLint("SimpleDateFormat")
    public static String getNowTime() {
        SimpleDateFormat s_format = new SimpleDateFormat("HH:mm:ss");
        return s_format.format(new Date());
    }

    @SuppressLint("SimpleDateFormat")
    public static String getNowTimeDetail() {
        SimpleDateFormat s_format = new SimpleDateFormat("HH:mm:ss.SSS");
        return s_format.format(new Date());
    }

}

UserInfo类：

class UserInfo {
    //行ID
    public long rowid;
    public int xuhao;
    public String name;
    public int age;
    public long height;
    public float weight;
    public boolean married;
    //用到DateUtil
    public String update_time;
    public String phone;
    public String password;

    public UserInfo() {
        rowid = 0l;
        xuhao = 0;
        name = "";
        age = 0;
        height = 0l;
        weight = 0.0f;
        married = false;
        update_time = "";
        phone = "";
        password = "";
    }
}

XML文件

xml version="1.0" encoding="utf-8"?>
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"
    android:focusable="true"
    android:focusableInTouchMode="true"
    android:orientation="vertical"
    android:padding="10dp"
    tools:context="com.victory.wangyalun.sqlitewriteactivity.SQLiteWriteActivity">

            android:layout_width="match_parent"
        android:layout_height="50dp" >

                    android:id="@+id/tv_name"
            android:layout_width="wrap_content"
            android:layout_height="match_parent"
            android:layout_alignParentLeft="true"
            android:gravity="center"
            android:text="姓名："
            android:textColor="@color/black"
            android:textSize="17sp" />

                    android:id="@+id/et_name"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_marginBottom="5dp"
            android:layout_marginTop="5dp"
            android:layout_toRightOf="@+id/tv_name"
            android:gravity="left|center"
            android:hint="请输入姓名"
            android:inputType="text"
            android:maxLength="12"
            android:textColor="@color/black"
            android:textColorHint="@color/black"
            android:textSize="17sp" />
    

            android:layout_width="match_parent"
        android:layout_height="50dp" >

                    android:id="@+id/tv_age"
            android:layout_width="wrap_content"
            android:layout_height="match_parent"
            android:layout_alignParentLeft="true"
            android:gravity="center"
            android:text="年龄："
            android:textColor="@color/black"
            android:textSize="17sp" />

                    android:id="@+id/et_age"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_marginBottom="5dp"
            android:layout_marginTop="5dp"
            android:layout_toRightOf="@+id/tv_age"
            android:gravity="left|center"
            android:hint="请输入年龄"
            android:inputType="number"
            android:maxLength="2"
            android:textColor="@color/black"
            android:textColorHint="@color/black"
            android:textSize="17sp" />
    

            android:layout_width="match_parent"
        android:layout_height="50dp" >

                    android:id="@+id/tv_height"
            android:layout_width="wrap_content"
            android:layout_height="match_parent"
            android:layout_alignParentLeft="true"
            android:gravity="center"
            android:text="身高："
            android:textColor="@color/black"
            android:textSize="17sp" />

                    android:id="@+id/et_height"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_marginBottom="5dp"
            android:layout_marginTop="5dp"
            android:layout_toRightOf="@+id/tv_height"
            android:gravity="left|center"
            android:hint="请输入身高"
            android:inputType="number"
            android:maxLength="3"
            android:textColor="@color/black"
            android:textColorHint="@color/black"
            android:textSize="17sp" />
    

            android:layout_width="match_parent"
        android:layout_height="50dp" >

                    android:id="@+id/tv_weight"
            android:layout_width="wrap_content"
            android:layout_height="match_parent"
            android:layout_alignParentLeft="true"
            android:gravity="center"
            android:text="体重："
            android:textColor="@color/black"
            android:textSize="17sp" />

                    android:id="@+id/et_weight"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_marginBottom="5dp"
            android:layout_marginTop="5dp"
            android:layout_toRightOf="@+id/tv_weight"
            android:gravity="left|center"
            android:hint="请输入体重"
            android:inputType="numberDecimal"
            android:maxLength="5"
            android:textColor="@color/black"
            android:textColorHint="@color/black"
            android:textSize="17sp" />
    

            android:layout_width="match_parent"
        android:layout_height="50dp" >

                    android:id="@+id/tv_married"
            android:layout_width="wrap_content"
            android:layout_height="match_parent"
            android:layout_alignParentLeft="true"
            android:gravity="center"
            android:text="婚否："
            android:textColor="@color/black"
            android:textSize="17sp" />

                    android:id="@+id/sp_married"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_toRightOf="@+id/tv_married"
            android:gravity="left|center"
            android:spinnerMode="dialog" />
    

            android:id="@+id/btn_save"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="保存到数据库"
        android:textColor="@color/black"
        android:textSize="20sp" />
            android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="查看数据"
        android:textColor="@color/black"
        android:textSize="20sp"
        android:id="@+id/btn_look"
        android:onClick="LookonClick"
        />