Android——数据库相关（课堂整理）

<?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>

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);
}
}
}
}