Android数据库SQLite的使用

1.简介

SQLite是一个小巧的嵌入式数据库，它的多数语法和Oracle一样（还好这个学期学了数据库）。SQLiteDataBase是SQLite的数据库管理类，具有创建，删除，执行SQL命令以及执行其他常见数据库管理任务的方法。SQLiteOpenHelper是用于管理数据库创建和版本管理的帮助程序类，是个抽象类，一般我们会创建创建一个子类继承自SQLiteOpenHelper实现onCreate(SQLiteDatabase)，onUpgrade(SQLiteDatabase, int, int))。onCreate方法只在第一次打开数据库的时候执行，所以重写这个方法时可以创建表。

2.例子

创建SQLiteActivity，写好辅助类UserDbHelper继承自SQLiteOpenHelper。

1. UserInfo.java。包装用户信息。

package xyz.strasae.androidlearn.my.bean;

public class UserInfo {
public String id;
public String password;
}

1. UserDbHelper.java。辅助类。

package xyz.strasae.androidlearn.my;

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

import java.util.ArrayList;

import xyz.strasae.androidlearn.my.bean.UserInfo;

/**
* 单例模式 确保只打开一次
*/
public class UserDbHelper extends SQLiteOpenHelper {
private static final String DB_NAME = "user.db";
private static final int DB_VERSION = 1;
private static UserDbHelper userDBHelper = null;
private SQLiteDatabase sqLiteDatabase = null;
private static final String TABLE_NAME = "user_info";

/*单例模式 构造器私有*/
private UserDbHelper(Context context) {
super(context, DB_NAME, null, DB_VERSION);
}

/*单例模式 构造器私有*/
private UserDbHelper(Context context, int db_version) {
super(context, DB_NAME, null, db_version);
}

/*单例模式 提供对外的接口*/
public static UserDbHelper getInstance(Context context, int db_version) {
if(db_version > 0 && userDBHelper == null) {
userDBHelper = new UserDbHelper(context, db_version);
} else if(userDBHelper == null) {
userDBHelper = new UserDbHelper(context);
}
return userDBHelper;
}

/*打开写连接*/
public SQLiteDatabase openWriteLink() {
if(sqLiteDatabase == null || sqLiteDatabase.isOpen() != true) {
sqLiteDatabase = userDBHelper.getWritableDatabase();
}
return sqLiteDatabase;
}

/*打开读连接*/
public SQLiteDatabase openReadLink() {
if(sqLiteDatabase == null || sqLiteDatabase.isOpen() != true) {
sqLiteDatabase = userDBHelper.getReadableDatabase();
}
return sqLiteDatabase;
}

/*关闭连接*/
public void closeLink() {
if(sqLiteDatabase != null && sqLiteDatabase.isOpen() == true) {
sqLiteDatabase.close();
sqLiteDatabase = null;
}
}

/*获取数据库名称*/
public String getDbName() {
if(userDBHelper != null) {
return userDBHelper.getDatabaseName();
} else {
return DB_NAME;
}
}

@Override
/*创建表*/
public void onCreate(SQLiteDatabase sqLiteDatabase) {
String drop_sql = "DROP TABLE IF EXISTS " + TABLE_NAME + ";";
sqLiteDatabase.execSQL(drop_sql);
String create_sql =  "CREATE TABLE IF NOT EXISTS " + TABLE_NAME + "(_id INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL," +
"user_id VARCHAR NOT NULL, password VARCHAR NOT NULL);";
sqLiteDatabase.execSQL(create_sql);
}

@Override
/*数据库升级，注意一次只能添加一列 第二个参数表示oldVersion 第三个参数表示newVersion*/
public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {
if (i1 > 1) {
String alter_sql = "ALTER TABLE " + TABLE_NAME + " ADD COLUMN " + "phone VARCHAR;";
sqLiteDatabase.execSQL(alter_sql);
}
}

/*删除指定关键字的记录 condition是where后的条件*/
public int delete(String condition) {
return sqLiteDatabase.delete(TABLE_NAME, condition, null);
}

/*删除所有记录（0=0是永远成立的）*/
public int deleteAll() {
return sqLiteDatabase.delete(TABLE_NAME, "0=0", null);
}

/*插入*/
public long insert(ArrayList<UserInfo> infoArrayList) {
long result = -1;
for(int i = 0; i < infoArrayList.size(); i++) {
UserInfo userInfo = infoArrayList.get(i);
ContentValues contentValues = new ContentValues();
contentValues.put("user_id", userInfo.id);
contentValues.put("password", userInfo.password);
result = sqLiteDatabase.insert(TABLE_NAME, "", contentValues);
}
return result;
}

public long insert(UserInfo userInfo) {
ContentValues contentValues = new ContentValues();
contentValues.put("user_id", userInfo.id);
contentValues.put("password", userInfo.password);
return sqLiteDatabase.insert(TABLE_NAME, "", contentValues);
}

/*查询*/
public ArrayList<UserInfo> query(String condition) {
String sql = String.format("select _id,user_id,password" +
" from %s where %s;", TABLE_NAME, condition);
ArrayList<UserInfo> infoArray = new ArrayList<UserInfo>();
Cursor cursor = sqLiteDatabase.rawQuery(sql, null);
if(cursor.moveToFirst()) {
for(;;cursor.moveToNext()) {
UserInfo userInfo = new UserInfo();
userInfo.id = cursor.getString(1);
userInfo.password = cursor.getString(2);
infoArray.add(userInfo);
if (cursor.isLast() == true) {
break;
}
}
}
cursor.close();
return infoArray;
}
}

1. activity_sqlite.xml

<?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://
3ff7
schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".SQLiteActivity"
android:orientation="vertical"
android:padding="10dp">

<!--注意ScrollView下只能挂一个节点-->
<ScrollView
android:layout_width="match_parent"
android:layout_height="wrap_content">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="50dp">

<TextView
android:id="@+id/tv_id"
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:textColor="#000000"
android:text="账号："
android:textSize="18sp"
android:layout_alignParentLeft="true"
android:gravity="center_vertical"/>

<EditText
android:id="@+id/et_id"
android:inputType="number"
android:maxLength="11"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:hint="账号"
android:layout_toRightOf="@id/tv_id"/>
</RelativeLayout>

<RelativeLayout
android:layout_width="match_parent"
android:layout_height="50dp">

<TextView
android:id="@+id/tv_password"
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:textColor="#000000"
android:text="密码："
android:textSize="18sp"
android:layout_alignParentLeft="true"
android:gravity="center_vertical"/>

<EditText
android:id="@+id/et_password"
android:inputType="textPassword"
android:maxLength="15"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:hint="密码"
android:layout_toRightOf="@id/tv_password"/>
</RelativeLayout>

<!--textAllCaps属性设置大小写（默认全部大写）-->
<Button
android:textAllCaps="false"
android:id="@+id/btn_ok"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="存入SQLite"/>

<EditText
android:id="@+id/et_input_id"
android:inputType="number"
android:maxLength="11"
android:hint="请输入要删除的id"
android:layout_marginTop="50dp"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
<Button
android:textAllCaps="false"
android:text="从SQLite删除指定数据"
android:id="@+id/btn_delete"
android:layout_width="match_parent"
android:layout_height="wrap_content" />

<Button
android:textAllCaps="false"
android:id="@+id/btn_query"
android:layout_marginTop="50dp"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="从SQLite中查询数据"
/>

<TextView
android:id="@+id/tv_show_data"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:textSize="18sp"
android:textColor="#000000"
android:hint="用于展示查询结果"
/>
</LinearLayout>
</ScrollView>
</LinearLayout>

1. SQLiteActivity.java

package xyz.strasae.androidlearn.my;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.text.TextUtils;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

import java.util.ArrayList;

import xyz.strasae.androidlearn.my.bean.UserInfo;

public class SQLiteActivity extends AppCompatActivity {
private UserDbHelper userDbHelper;
private EditText et_id;
private EditText et_password;
private TextView tv_show_data;
private EditText et_input_id;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_sqlite);
et_id = findViewById(R.id.et_id);
et_password = findViewById(R.id.et_password);
tv_show_data = findViewById(R.id.tv_show_data);
et_input_id = findViewById(R.id.et_input_id);
findViewById(R.id.btn_ok).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
if(userDbHelper==null) {
Toast.makeText(SQLiteActivity.this, "数据库连接为空", Toast.LENGTH_SHORT).show();
return;
}
userDbHelper.openWriteLink();
String id = et_id.getText().toString();
String password = et_password.getText().toString();
if(TextUtils.isEmpty(id)) {
Toast.makeText(SQLiteActivity.this, "请先填写账号！", Toast.LENGTH_SHORT).show();
return ;
} else if(TextUtils.isEmpty(password)){
Toast.makeText(SQLiteActivity.this, "密码不能为空！", Toast.LENGTH_SHORT).show();
return ;
}
UserInfo userInfo = new UserInfo();
userInfo.id = id;
userInfo.password = password;
userDbHelper.insert(userInfo);
Toast.makeText(SQLiteActivity.this, "存入数据库成功！", Toast.LENGTH_SHORT).show();
}
});
findViewById(R.id.btn_query).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
if(userDbHelper==null) {
Toast.makeText(SQLiteActivity.this, "数据库连接为空", Toast.LENGTH_SHORT).show();
return;
}
userDbHelper.openReadLink();
ArrayList<UserInfo> userArray = userDbHelper.query("1=1");
String desc = String.format("数据库查询到%d条记录，详情如下：", userArray.size());
if(userArray == null || userArray.size() <= 0) {
desc = "查询结果为空";
}
for (int i=0; i<userArray.size(); i++) {
UserInfo info = userArray.get(i);
desc = String.format("%s\n第%d条记录信息如下：", desc, i+1);
desc = String.format("%s\n　id：%s", desc, info.id);
desc = String.format("%s\n　password：%s", desc, info.password);
}
tv_show_data.setText(desc);
}
});
findViewById(R.id.btn_delete).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
if(userDbHelper==null) {
Toast.makeText(SQLiteActivity.this, "数据库连接为空", Toast.LENGTH_SHORT).show();
return;
}
userDbHelper.openReadLink();
int count = userDbHelper.delete("user_id=" + et_input_id.getText().toString());
Toast.makeText(SQLiteActivity.this, "成功删除" + count + "条数据", Toast.LENGTH_SHORT).show();
}
});
}

protected void onStart() {
super.onStart();
userDbHelper = UserDbHelper.getInstance(this, 2);
}

@Override
protected void onStop() {
super.onStop();
if(userDbHelper != null)
userDbHelper.closeLink();
}
}