哪一个网站有做实验的过程,培训机构网站,深圳画册设计推荐,浏览加速器SQLiteOpenHelper数据库帮助器是Android提供的数据库辅助工具。
1、继承SQLiteOpenHelper类#xff0c;需要重写onCreate和onUpgrade两个方法
案例#xff1a;实现增删改查
package com.example.databases_text;import android.app.PictureInPictureParams;
import androi…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;Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);edit_namefindViewById(R.id.et_name);edit_passwordfindViewById(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);}Overrideprotected 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();}Overrideprotected void onDestroy() {super.onDestroy();}Overridepublic void onClick(View view) {User user new User();String nameedit_name.getText().toString();String pswedit_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:ListUser userListmUserDBHelper.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;}Overridepublic 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 instancenull;private SQLiteDatabase mRDBnull;private SQLiteDatabase mWDBnull;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(instancenull){instancenew UserDBHelper(context);}return instance;}//打开数据库的读连接public SQLiteDatabase openReadLink(){if(mRDBnull || !mRDB.isOpen()) {mRDB instance.getReadableDatabase();}return mRDB;}//打开数据库的写连接public SQLiteDatabase openWriteLink(){if(mWDBnull || !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Overridepublic void onCreate(SQLiteDatabase sqLiteDatabase) {String sql create table TABLE_NAME ( COLUMN_NAME text, COLUMN_PASSWORD text);sqLiteDatabase.execSQL(sql);}Overridepublic 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 ListUser queryData(String name){ListUser 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 user1new User();user1.setName(cursor.getString(0));user1.setPassword(cursor.getString(1));list.add(user1);}return list;}}
?xml version1.0 encodingutf-8?
LinearLayout xmlns:androidhttp://schemas.android.com/apk/res/androidxmlns:apphttp://schemas.android.com/apk/res-autoxmlns:toolshttp://schemas.android.com/toolsandroid:layout_widthmatch_parentandroid:layout_heightmatch_parenttools:context.MainActivityandroid:orientationverticalTextViewandroid:layout_widthmatch_parentandroid:layout_heightwrap_contentandroid:text用户名/EditTextandroid:idid/et_nameandroid:layout_widthmatch_parentandroid:layout_heightwrap_content/TextViewandroid:layout_widthmatch_parentandroid:layout_heightwrap_contentandroid:text密码/EditTextandroid:idid/et_pwsandroid:layout_widthmatch_parentandroid:layout_heightwrap_content/Buttonandroid:layout_widthmatch_parentandroid:layout_heightwrap_contentandroid:idid/btn_addandroid:text添加/Buttonandroid:layout_widthmatch_parentandroid:layout_heightwrap_contentandroid:idid/btn_delandroid:text删除/Buttonandroid:layout_widthmatch_parentandroid:layout_heightwrap_contentandroid:idid/btn_updateandroid:text修改/Buttonandroid:layout_widthmatch_parentandroid:layout_heightwrap_contentandroid:idid/btn_queryandroid:text查询/
/LinearLayout 2、onUpgrade()是在数据库版本更新时执行操作。
