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,\n" +
                     "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);
             }
         }
     }
 }