SQLiteOpenHelper数据库帮助器是Android提供的数据库辅助工具。
1、继承SQLiteOpenHelper类，需要重写onCreate和onUpgrade两个方法
案例：实现增删改查
package com.example.databases_text;
import android.app.PictureInPictureParams;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.content.res.Configuration;
import android.os.Bundle;
import android.text.TextUtils;
import android.util.Log;
import android.util.Rational;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
import androidx.appcompat.app.AppCompatActivity;
import com.example.databases_text.R;
import java.util.List;
public class MainActivity extends AppCompatActivity implements View.OnClickListener{
private EditText edit_name;
private EditText edit_password;
private UserDBHelper mUserDBHelper;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
edit_name=findViewById(R.id.et_name);
edit_password=findViewById(R.id.et_pws);
findViewById(R.id.btn_add).setOnClickListener(this);
findViewById(R.id.btn_del).setOnClickListener(this);
findViewById(R.id.btn_update).setOnClickListener(this);
findViewById(R.id.btn_query).setOnClickListener(this);
}
@Override
protected void onStart() {
super.onStart();
//获得数据库帮助器实例
mUserDBHelper = UserDBHelper.getInstance(this);
mUserDBHelper.openWriteLink();//打开数据库
mUserDBHelper.openReadLink();
}
@Override
protected void onDestroy() {
super.onDestroy();
}
@Override
public void onClick(View view) {
User user = new User();
String name=edit_name.getText().toString();
String psw=edit_password.getText().toString();
switch (view.getId()){
case R.id.btn_add:
user.setName(name);
user.setPassword(psw);
if( mUserDBHelper.InsertData(user)>0)
Toast.makeText(this,"添加成功", Toast.LENGTH_SHORT).show();
break;
case R.id.btn_del:
user.setName(name);
user.setPassword(psw);
if( mUserDBHelper.deleteData(user)>0)
Toast.makeText(this,"删除成功", Toast.LENGTH_SHORT).show();
break;
case R.id.btn_update:
user.setName(name);
user.setPassword(psw);
if( mUserDBHelper.updateData(user)>0)
Toast.makeText(this,"修改成功", Toast.LENGTH_SHORT).show();
break;
case R.id.btn_query:
List<User> userList=mUserDBHelper.queryData(name);
if(userList !=null){
edit_password.setText(userList.get(0).getPassword());
//userList.get(x).getPassword()表示查询第几个的密码
Toast.makeText(this,"查询成功", Toast.LENGTH_SHORT).show();}
break;
}
}
}package com.example.databases_text;
public class User {
private String name;
private String password;
public User() {
}
public User(String name, String password) {
this.name = name;
this.password = password;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
@Override
public String toString() {
return "User{" +
"name='" + name + '\'' +
", password='" + password + '\'' +
'}';
}
}
package com.example.databases_text;
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 java.util.List;
public class UserDBHelper extends SQLiteOpenHelper {
// 数据库版本号
public static final int DATABASE_VERSION = 1;
// 数据库名称
public static final String DATABASE_NAME = "User.db";
public static final String DATABASE_table_name = "uer_table";
// 用户表名
public static final String TABLE_NAME = "user";
// 用户名
public static final String COLUMN_NAME = "name";
// 用户密码
public static final String COLUMN_PASSWORD = "password";
private static UserDBHelper instance=null;
private SQLiteDatabase mRDB=null;
private SQLiteDatabase mWDB=null;
public UserDBHelper( Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
//利用单例模式，获取数据库的唯一实例,当数据库不存在的时候，经行创建，如果已存在就直接返回
public static UserDBHelper getInstance(Context context){
if(instance==null){
instance=new UserDBHelper(context);
}
return instance;
}
//打开数据库的读连接
public SQLiteDatabase openReadLink(){
if(mRDB==null || !mRDB.isOpen()) {
mRDB = instance.getReadableDatabase();
}
return mRDB;
}
//打开数据库的写连接
public SQLiteDatabase openWriteLink(){
if(mWDB==null || !mWDB.isOpen()) {
mWDB = instance.getReadableDatabase();
}
return mWDB;
}
//数据库的关闭操作
public void closeLink() {
if (mRDB != null && mRDB.isOpen()) {
mRDB.close();
mRDB = null;
}
if (mWDB != null && mWDB.isOpen()) {
mWDB.close();
mWDB = null;//置为空为了回收
}
}
//创建数据库，执行sql语句
@Override
public void onCreate(SQLiteDatabase sqLiteDatabase) {
String sql = "create table " + TABLE_NAME + " (" + COLUMN_NAME + " text, " + COLUMN_PASSWORD
+ " text)";
sqLiteDatabase.execSQL(sql);
}
@Override
public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {
}
//添加数据到数据库
public long InsertData(User user){
ContentValues values = new ContentValues();
values.put("name", user.getName());
values.put("password", user.getPassword());
return mWDB.insert(TABLE_NAME,null,values);
}
public long deleteData(User user){
//删除所有的
return mWDB.delete(TABLE_NAME,"name=? and password=?",new String[]{user.getName(),user.getPassword()});
}
public long updateData(User user){
ContentValues values = new ContentValues();
values.put("name", user.getName());
values.put("password", user.getPassword());
//更改所有符合条件的数据
return mWDB.update(TABLE_NAME,values,"name=? ",new String[]{user.getName()});
}
public List<User> queryData(String name){
List<User> list = new ArrayList<>();
//查询所有数据，得到游标
Cursor cursor =mWDB.query(TABLE_NAME,null,"name=? ",new String[]{name},null,null,null);
//逐个取出游标指向的数据
while (cursor.moveToNext()){
User user1=new User();
user1.setName(cursor.getString(0));
user1.setPassword(cursor.getString(1));
list.add(user1);
}
return list;
}
}<?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://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity"
android:orientation="vertical">
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="用户名"/>
<EditText
android:id="@+id/et_name"
android:layout_width="match_parent"
android:layout_height="wrap_content"
/>
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="密码"/>
<EditText
android:id="@+id/et_pws"
android:layout_width="match_parent"
android:layout_height="wrap_content"
/>
<Button
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="@+id/btn_add"
android:text="添加"
/>
<Button
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="@+id/btn_del"
android:text="删除"
/>
<Button
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="@+id/btn_update"
android:text="修改"
/>
<Button
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="@+id/btn_query"
android:text="查询"
/>
</LinearLayout>
2、onUpgrade()是在数据库版本更新时，执行操作。
