Android——数据库相关（课堂整理）

layout文件：

<?xml version="1.0" encoding="utf-8"?>
<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:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.hanqi.testapp3.TestActivity"
    android:orientation="vertical">

    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="初始化数据库"
        android:onClick="bt1_onClick"/>
    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="升级数据库"
        android:onClick="bt2_onClick"/>
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content">
        <EditText
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:id="@+id/et_id"
            android:hint="id"/>
        <EditText
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:id="@+id/et_name"
            android:hint="name"/>
    </LinearLayout>
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content">
        <EditText
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:id="@+id/et_sex"
            android:hint="sex"/>
        <EditText
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:id="@+id/et_age"
            android:hint="age"/>
    </LinearLayout>
    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="新增数据"
        android:onClick="bt3_onClick"/>
    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="查询数据"
        android:onClick="bt4_onClick"/>
    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="带条件查询数据"
        android:onClick="bt5_onClick"/>
    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="修改数据"
        android:onClick="bt6_onClick"/>
    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="删除数据"
        android:onClick="bt7_onClick"/>
    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="数据库事务"
        android:onClick="bt8_onClick"/>
</LinearLayout>

java类：

package com.hanqi.testapp3;

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

public class TestActivity extends AppCompatActivity {

    EditText et_id,et_name,et_sex,et_age;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_test);
        et_id = (EditText)findViewById(R.id.et_id);
        et_name = (EditText)findViewById(R.id.et_name);
        et_sex = (EditText)findViewById(R.id.et_sex);
        et_age = (EditText)findViewById(R.id.et_age);
    }
    //初始化数据库
    public void bt1_onClick(View v)
    {
        //使用工具类得到数据库对象
        MyDBHelper myDBHelper = new MyDBHelper("test.db",1);
        Toast.makeText(TestActivity.this, "连接数据库成功", Toast.LENGTH_SHORT).show();
        //得到连接
        SQLiteDatabase sqLiteDatabase = myDBHelper.getWritableDatabase();
        //关闭连接
        sqLiteDatabase.close();
    }
    //升级数据库
    public void bt2_onClick(View v)
    {
        //使用工具类得到数据库对象
        MyDBHelper myDBHelper = new MyDBHelper("test.db",2);
        Toast.makeText(TestActivity.this, "连接数据库成功", Toast.LENGTH_SHORT).show();
        //得到连接
        SQLiteDatabase sqLiteDatabase = myDBHelper.getWritableDatabase();
        //关闭连接
        sqLiteDatabase.close();
    }
    //插入新数据
    public void bt3_onClick(View v)
    {
        //1.连接数据库，得到数据库连接对象
        //得到连接
        SQLiteDatabase sd = new MyDBHelper("test.db",2).getWritableDatabase();
        //2.准备数据
        ContentValues cv = new ContentValues();
        cv.put("name",et_name.getText().toString());
        cv.put("sex",et_sex.getText().toString());
        cv.put("age", et_age.getText().toString());
        //3.调用insert()，插入数据
        long l = sd.insert("t_user", null, cv);
        Toast.makeText(TestActivity.this, "插入数据的主键 = "+l, Toast.LENGTH_SHORT).show();
        //4.关闭连接
        sd.close();
    }
    //数据查询
    public void bt4_onClick(View v)
    {
        //1.连接数据库，得到数据库连接对象
        //得到连接
        SQLiteDatabase sd = new MyDBHelper("test.db",2).getWritableDatabase();
        //2.全表全字段查询
        Cursor c = sd.query("t_user", null, null, null, null, null, null);
        //3.遍历结果集
        while (c.moveToNext())
        {
            //读取数据
            String str ="_id ="+c.getLong(c.getColumnIndex("_id"))+"name = "
                    +c.getString(1)+" sex = "+c.getString(2)+
                    " age = "+c.getInt(3);
            Log.e("TAG",str);
        }
        Toast.makeText(TestActivity.this, "结果集的记录条数 = "+c.getCount(), Toast.LENGTH_SHORT).show();
        c.close();
        //4.关闭连接
        sd.close();
    }
    //带条件数据查询
    public void bt5_onClick(View v)
    {
        //1.连接数据库，得到数据库连接对象
        //得到连接
        SQLiteDatabase sd = new MyDBHelper("test.db",2).getWritableDatabase();
        String strwhere = "1 = 1";
        //select * from t_user where _id = 1 and name like '%张%' and sex = ''
        //得到条件
        if (et_id.getText().length()>0)
        {
            strwhere += " and _id = "+et_id.getText().toString();
        }

        if (et_name.getText().length()>0)
        {
            strwhere += " and name like '%"+et_name.getText().toString()+"%'";
        }
        if (et_sex.getText().length()>0)
        {
            strwhere += " and sex = "+et_sex.getText().toString()+"'";
        }
        if (et_age.getText().length()>0)
        {
            strwhere += " and age = '"+et_age.getText().toString()+"'";
        }
        //2.查询
        Cursor c = sd.query("t_user", null, strwhere, null, null, null, null);
        //3.遍历结果集
        while (c.moveToNext())
        {
            //读取数据
            String str ="_id ="+c.getLong(c.getColumnIndex("_id"))+"name = "
                    +c.getString(1)+" sex = "+c.getString(2)+
                    " age = "+c.getInt(3);
            Log.e("TAG",str);
        }
        Toast.makeText(TestActivity.this, "结果集的记录条数 = "+c.getCount(), Toast.LENGTH_SHORT).show();
        c.close();
        //4.关闭连接
        sd.close();
    }
    //修改数据
    public void bt6_onClick(View v)
    {
        //1.连接数据库，得到数据库连接对象
        //得到连接
        SQLiteDatabase sd = new MyDBHelper("test.db",2).getWritableDatabase();
        //2.修改
        ContentValues cv = new ContentValues();
        cv.put("name",et_name.getText().toString());
        cv.put("sex",et_sex.getText().toString());
        cv.put("age", et_age.getText().toString());
        int i = sd.update("t_user",cv,"_id = ?",new String[]{et_id.getText().toString()});
        Toast.makeText(TestActivity.this, "修改的记录条数 = "+i, Toast.LENGTH_SHORT).show();
        //4.关闭连接
        sd.close();
    }
    //删除数据
    public void bt7_onClick(View v)
    {
        //1.连接数据库，得到数据库连接对象
        //得到连接
        SQLiteDatabase sd = new MyDBHelper("test.db",2).getWritableDatabase();
        //2.删除
        int i = sd.delete("t_user", "_id = ?", new String[]{et_id.getText().toString()});
        Toast.makeText(TestActivity.this, "修改的记录条数 = "+i, Toast.LENGTH_SHORT).show();
        //4.关闭连接
        sd.close();
    }
    //数据库事务
    public void bt8_onClick(View v)
    {

        //1.连接数据库，得到数据库连接对象
        //得到连接
        SQLiteDatabase sd = new MyDBHelper("test.db", 2).getWritableDatabase();
        try {
            //启动事务
            sd.beginTransaction();
            //2.修改
            ContentValues cv1 = new ContentValues();
            cv1.put("age", "43");
            ContentValues cv2 = new ContentValues();
            cv2.put("age", "53");
            //修改1
            int i = sd.update("t_user", cv1, "_id = 1", null);
            //抛出异常
            if (i > 0) {
                throw new RuntimeException("模拟事务异常");
            }
            //修改2
            int k = sd.update("t_user", cv2, "_id = 2", null);
            //设置事务是成功完成的
            sd.setTransactionSuccessful();

            Toast.makeText(TestActivity.this, "修改的记录条数 = " + (i + k), Toast.LENGTH_SHORT).show();

        }
        catch (Exception e)
        {
            e.printStackTrace();
        }
        finally {
            //一定会被执行的代码
            //结束事务
            //1.没有异常，提交事务
            //2.发生异常，回滚事务
            sd.endTransaction();
            //4.关闭连接
            sd.close();
        }
    }
    //实现SQLiteOpenHelper的内部类
    class MyDBHelper extends SQLiteOpenHelper
    {
        //构造方法
        public MyDBHelper(String dbname,int ver)
        {
            //显示调用父类的构造方法
            //必须在第一行
            super(TestActivity.this,dbname,null,ver);
        }
        //创建和初始化数据库
        @Override
        public void onCreate(SQLiteDatabase db) {
            //1.执行创建数据库的语句
            String sql = "CREATE TABLE t_user " +
                    "(_id  INTEGER NOT NULL," +
                    "name  VARCHAR(20) NOT NULL," +
                    "sex  CHAR(1),age  INTEGER,
" +
                    "PRIMARY KEY ("_id"))";
            db.execSQL(sql);
            Log.e("TAG","表创建成功");
            //2.执行初始化数据的语句，insert语句
            ContentValues cv = new ContentValues();
            cv.put("name","张三");
            cv.put("sex","男");
            cv.put("age",20);
            //执行插入，返回主键
            long l = db.insert("t_user",null,cv);
            Log.e("TAG","初始化数据 = "+l);

        }
        //升级数据库
        //触发条件：当版本号增大
        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
            //修改数据
            if (newVersion ==2)
            {
                ContentValues cv = new ContentValues();
                cv.put("name","李四");
                String sql = "update t_user set name='李四'where _id=1";
                String[] str = {"1","18"};
                //调用db的更新方法
                int i = db.update("t_user",cv,"_id=? and age>?",str);
                Log.e("TAG","升级数据 数据条数 = "+i);
            }
        }
    }
}