Android学习（十） SQLite 基于SQLiteOpenHelper的操作方式

main.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity" >

    <Button
        android:id="@+id/button1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="插入数据" />

    <Button
        android:id="@+id/button2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="读取数据" />

    <Button
        android:id="@+id/button3"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="修改数据" />

    <Button
        android:id="@+id/button4"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="删除数据" />

</LinearLayout>

DBOpenHelper.java

package com.example.sqlitedemo3;

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

public class DBOpenHelper extends SQLiteOpenHelper{

    //实例化时，指定创建数据库的名称
    public DBOpenHelper(Context context, String name) {
        super(context, name, null, 1);
    }

    @Override  //当第一次创建数据库时调用，系统自动调用，只执行一次
    public void onCreate(SQLiteDatabase db) {
        //第一次执行时，创建tb_user表
        db.execSQL("create table if not exists tb_user(id integer primary key autoincrement,name text not null,age integer not null,sex text not null)");
    }

    @Override  //当数据库版本发生改变时调用，系统自动调用
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    }

}

main.java

package com.example.sqlitedemo3;

import android.os.Bundle;
import android.app.Activity;
import android.content.ContentValues;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.Toast;

public class MainActivity extends Activity {

    Button btnAdd;
    Button btnQuery;
    Button btnUpdate;
    Button btnDelete;
    SQLiteDatabase db;
    DBOpenHelper helper;

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

        //创建DBOpenHelper对象，第一个参数为调用的activity，第二个参数为数据库的名称
        helper = new DBOpenHelper(MainActivity.this, "user.db");        

        btnAdd = (Button) findViewById(R.id.button1);
        btnQuery = (Button) findViewById(R.id.button2);
        btnUpdate = (Button) findViewById(R.id.button3);
        btnDelete = (Button) findViewById(R.id.button4);

        btnAdd.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                //只是可写的数据库对象
                db = helper.getWritableDatabase();

                ContentValues values = new ContentValues();
                values.put("name", "李四");
                values.put("age", 20);
                values.put("sex", "女");
                db.insert("tb_user", null, values);
                values.clear();

                values.put("name", "王五");
                values.put("age", 22);
                values.put("sex", "男");
                db.insert("tb_user", null, values);
                Toast.makeText(MainActivity.this, "添加成功", 1).show();

                db.close();
            }
        });

        btnQuery.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                //只是可写的数据库对象
                db = helper.getReadableDatabase();
                //其他方法和前面没有区别
                Cursor cur = db.query("tb_user", new String[]{"id","name","age","sex"}, null, null, null, null, null);
                while(cur.moveToNext()){
                    int id = cur.getInt(0);
                    String name = cur.getString(cur.getColumnIndex("name"));
                    int age = cur.getInt(cur.getColumnIndex("age"));
                    String sex = cur.getString(cur.getColumnIndex("sex"));

                    Log.i("stuinfo",id + ","+ name + "," + age + "," + sex);
                }
                cur.close();
                db.close();
            }
        });

        btnUpdate.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                //修改数据
                db = helper.getWritableDatabase();
                ContentValues values = new ContentValues();
                values.put("name", "张三丰");
                int result = db.update("tb_user", values, "id=?", new String[]{"1"});
                if(result > 0)
                    Toast.makeText(MainActivity.this, "修改成功", 1).show();
                else
                    Toast.makeText(MainActivity.this, "修改失败", 1).show();
                db.close();
            }
        });

        btnDelete.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                db = helper.getWritableDatabase();
                //删除数据
                int result = db.delete("tb_user", "id=?", new String[]{"1"});
                if(result > 0)
                    Toast.makeText(MainActivity.this, "删除成功", 1).show();
                else
                    Toast.makeText(MainActivity.this, "删除失败", 1).show();
                db.close();
            }
        });
    }

}