Android SQLiteOpenHelper 的作用及使用

SQLiteOpenHelper是一个帮助类数据库管理的帮助类，让开发者直接操作这个类实现对数据库各种框架的完善

首先建立一个SQLiteOpenHelper文件，在这个文件里面进行数据框架的操作

下面是一个简单的一个小例子，主要是通过SQliteOpenHelper来完成  

1：首先建一个XML文件给4个按钮，分别表示 对数据库的添删改查，

 <-----------activity_main.xml------------->布局文件

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    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="com.yongninggo.helloworld2.MainActivity"
    android:orientation="vertical"
    android:gravity="center_horizontal">

    <Button
        android:id="@+id/btn"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="新建数据库"/>

    <Button
        android:id="@+id/btn1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="插入数据"/>

    <Button
        android:id="@+id/btn2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="修改数据"/>

    <Button
        android:id="@+id/btn3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="删除数据"/>

</LinearLayout>

<-----------DBopenhelper.Java------>文件,这个文件就是一个SQliteOpenHelper的帮助类

package com.yongninggo.helloworld2;

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

/**
 * SQLiteOpenHelper帮助类,
 */

public class DBopenhelper  extends SQLiteOpenHelper{

    public DBopenhelper(Context context, String name) {
        super(context, SQLValue.DATABASE_NAME, null, SQLValue.DATABASE_VERTION);
    }

    @Override       //创建数据库调用这个类
    public void onCreate(SQLiteDatabase db) {

        //创建数据表
        String sql =("create table if not exists "+SQLValue.DATABASE_TABLE+"" +
                "("+SQLValue._ID+" integer primary key autoincrement," +
                ""+SQLValue.TABLE_NAME+" text not null,"+SQLValue.TABLE_SEX+" text not null," +
                ""+SQLValue.TABLE_AGE+" integer not null)");

        //插入数据
        db.execSQL(sql);
    }

    @Override       //跟新版本调用这个类
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    }

}

其中的值全部写入里一个文件夹方便管理，修改

package com.yongninggo.helloworld2;
 <-----------SQLValue.java----------->布局文件
package com.yongninggo.helloworld2;

/**
 *  SQlite 数据值信息
 */

public class SQLValue {
    public static final String DATABASE_NAME ="pass.db";
    public static final int DATABASE_VERTION = 1;

    public static final String DATABASE_TABLE = "pass";

    public static final String _ID ="_id";
    public static final String TABLE_NAME = "name";
    public static final String TABLE_SEX = "sex";
    public static final String TABLE_AGE = "age";
}

<-----------MainActivity.java----------->布局文件 在这里进行对数据库的操作

package com.yongninggo.helloworld2;

import android.content.ContentValues;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.View;
import android.widget.Button;

public class MainActivity extends AppCompatActivity {

    private Button btn;
    private Button btn1;
    private Button btn2;
    private Button btn3;

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

        btn = (Button) findViewById(R.id.btn);
        btn1 = (Button) findViewById(R.id.btn1);
        btn2 = (Button) findViewById(R.id.btn2);
        btn3 = (Button) findViewById(R.id.btn3);

        btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                DBopenhelper helper = new DBopenhelper(MainActivity.this,"pass.db");

                SQLiteDatabase db = helper.getWritableDatabase();

                //返回游标对象的select 查询
                Cursor c = db.rawQuery("select * from pass",null);
                if (c != null){
                    String [] cols = c.getColumnNames();
                    while (c.moveToNext()){
                        for (String colsnames : cols){
                            Log.i("myc",colsnames+":"+c.getString(c.getColumnIndex(colsnames)));
                        }
                    }
                    c.close();
                }
                db.close();
            }
        });

        btn1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                //插入数据信息
                DBopenhelper helper = new DBopenhelper(MainActivity.this,"pass.db");
                SQLiteDatabase db = helper.getWritableDatabase();
                ContentValues values = new ContentValues();
                values.put("name","马延超");
                values.put("sex","男");
                values.put("age",20);
                db.insert("pass",null,values);
                values.clear();
                values.put("name","马超");
                values.put("sex","男");
                values.put("age",0);
                db.insert("pass",null,values);
                values.clear();
                values.put("name","马延");
                values.put("sex","男");
                values.put("age",2);
                db.insert("pass",null,values);
                values.clear();
            }
        });

        btn2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
               DBopenhelper helper = new DBopenhelper(MainActivity.this,"pass.db");
               SQLiteDatabase db = helper.getWritableDatabase();

                // 修改数据信息
                ContentValues values = new ContentValues();
                values.put("sex","女");
                db.update("pass",values,"_id> ?",new String[]{"3"});
            }
        });

        btn3.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                DBopenhelper helper = new DBopenhelper(MainActivity.this,"pass.db");
                SQLiteDatabase db = helper.getWritableDatabase();

                //删除数据信息
                db.delete("pass","name like ?",new String[]{"%延%"});
                Cursor c = db.query("pass",null,"_id > ?",new String[]{"0"},null,null,"age");
                if (c != null){
                    String[]columes = c.getColumnNames();
                    while (c.moveToNext()){
                        for (String columenames : columes){
                            Log.i("myc",c.getString(c.getColumnIndex(columenames)));
                        }
                    }
                    c.close();
                }
                db.close();
            }
        });

    }
}