Android 持久化技术

标签：findViewById 持久 val text 技术 id import Android android

1. 用户登陆界面

（ 1 ）创建一个 LoginActivity ，对应的布局文件 activity_login 。（ 2 ）具备两个 TextView 和两个 EditText 控件，分别用于显示和输入用户名和密码。（ 3 ）添加 “ 注册 ” 和 “ 登陆 ” 两个按钮（ Button ）。（ 4 ）添加 “ 记住我 ” 功能：插入一个 CheckBox 控件，当用户勾选该勾选框，当点击 “ 登陆 ” 按钮时，判断该勾选框，如果勾选，则把用户名和密码保存起来，要求采用文本存储方式保存下来。（ 5 ）点击 “ 注册 ” ，可以根据用户名和密码对应的 EditText ，将用户名和密码保存起来，要求采用 SharedPreferences 保存用户名和密码数据，同时需要确保用户名不重复（区分大小写）。（ 6 ）点击 “ 登陆 ” ，通过 SharedPreferences 读取用户密码数据，并进行匹配，只有匹配成功，才能成功登陆，跳转到 MainActivity （下一个设计内容）

2. 图书信息数据库和显示界面

（ 1 ）需要保存的信息：书本信息（下表左），和书本所属类别（下表右）。每本书有其所属的类别。

create table Book (
id integer primary key autoincrement,
author text,
price real,
pages integer,
name text

category_id integer

)

create table Category (
id integer primary key autoincrement
category_name text,
category_code integer)

使用 SqlLite 数据库创建数据库 library ，并创建 Book 和 Category 这两个表。往 Category 里插入 2 条默认书类别数据（如：经济类， 1 ）。（ 2 ）界面设计： ① 创建一个 MainActivity ，对应的布局为 activity_main 。 ② 添加一个 RecyclerView ，用于显示所有的图书条目信息，每个条目显示书的名字、作者、类别和价格。 ③ 添加一个 “ 添加书目 ” 的按钮，用于跳转进入 AddBookActivity 。 ④ 在 AddBookActivity 中，可以添加一本书的信息到数据库中。提示： AddBookActivity 需要的组件包括： EditText 、 TextView 、 Button 或 Spinner 。提醒：可以在 RecyclerView 的适配器里面进行数据库的查询操作。

3.应用运行功能的截图

登录成功后进入首页面：

4.源码

Book.kt data class Book( val author : String , val price : Double , val pages : Int , val name : String , val categoryId : Int ) Category.kt package com.example.mylibrary data class Category( val id : Int , val categoryName : String , val categoryCode : Int ) LoginActivity.kt package com.example.mylibrary import android.content.Context import android.content.Intent import android.content.SharedPreferences import androidx.appcompat.app.AppCompatActivity import android.os.Bundle import android.widget.Button import android.widget.CheckBox import android.widget.EditText import android.widget.Toast class LoginActivity : AppCompatActivity() { private lateinit var usernameEditText : EditText private lateinit var passwordEditText : EditText private lateinit var rememberMeCheckBox : CheckBox private lateinit var sharedPreferences : SharedPreferences override fun onCreate (savedInstanceState: Bundle?) { super .onCreate(savedInstanceState) setContentView(R.layout. activity_login ) usernameEditText = findViewById(R.id. usernameEditText ) passwordEditText = findViewById(R.id. passwordEditText ) rememberMeCheckBox = findViewById(R.id. rememberMeCheckBox ) val loginButton: Button = findViewById(R.id. loginButton ) val registerButton: Button = findViewById(R.id. registerButton ) sharedPreferences = getSharedPreferences( "MyPrefs" , Context. MODE_PRIVATE ) loginButton.setOnClickListener { val username = usernameEditText . text .toString() val password = passwordEditText . text .toString() if (validateLogin(username , password)) { if ( rememberMeCheckBox . isChecked ) { rememberUser(username , password) } val intent = Intent( this @LoginActivity , MainActivity:: class . java ) startActivity(intent) // finish() } else { Toast.makeText( this @LoginActivity , "Invalid username or password" , Toast. LENGTH_SHORT ).show() } } registerButton.setOnClickListener { val username = usernameEditText . text .toString() val password = passwordEditText . text .toString() if (registerUser(username , password)) { Toast.makeText( this @LoginActivity , "Registration successful" , Toast. LENGTH_SHORT ).show() } else { Toast.makeText( this @LoginActivity , "Username already exists" , Toast. LENGTH_SHORT ).show() } } } private fun validateLogin (username: String , password: String): Boolean { val storedPassword = sharedPreferences .getString(username , null ) return storedPassword == password } private fun rememberUser (username: String , password: String) { val editor = sharedPreferences .edit() editor.putString(username , password) editor.apply() } private fun registerUser (username: String , password: String): Boolean { if (! sharedPreferences .contains(username)) { val editor = sharedPreferences .edit() editor.putString(username , password) editor.apply() return true } return false } } activity_login.xml <? xml version ="1.0" encoding ="utf-8" ?> <RelativeLayout xmlns: android ="http://schemas.android.com/apk/res/android" android :layout_width ="match_parent" android :layout_height ="match_parent" android :padding ="16dp" > <TextView android :id ="@+id/usernameTextView" android :layout_width ="wrap_content" android :layout_height ="wrap_content" android :text ="Username" android :layout_marginBottom ="8dp" /> <EditText android :id ="@+id/usernameEditText" android :layout_width ="match_parent" android :layout_height ="wrap_content" android :layout_below ="@id/usernameTextView" android :hint ="Enter username" android :padding ="12dp" 10 android :layout_marginBottom ="16dp" /> <TextView android :id ="@+id/passwordTextView" android :layout_width ="wrap_content" android :layout_height ="wrap_content" android :layout_below ="@id/usernameEditText" android :text ="Password" android :layout_marginBottom ="8dp" /> <EditText android :id ="@+id/passwordEditText" android :layout_width ="match_parent" android :layout_height ="wrap_content" android :layout_below ="@id/passwordTextView" android :inputType ="textPassword" android :hint ="Enter password" android :padding ="12dp" android :layout_marginBottom ="16dp" /> <CheckBox android :id ="@+id/rememberMeCheckBox" android :layout_width ="wrap_content" android :layout_height ="wrap_content" android :text ="Remember me" android :layout_below ="@id/passwordEditText" android :layout_marginBottom ="16dp" /> <Button android :id ="@+id/loginButton" android :layout_width ="match_parent" android :layout_height ="wrap_content" android :text ="Login" android :layout_below ="@id/rememberMeCheckBox" android :layout_marginBottom ="8dp" /> <Button android :id ="@+id/registerButton" android :layout_width ="match_parent" android :layout_height ="wrap_content" android :text ="Register" android :layout_below ="@id/loginButton" /> </RelativeLayout> MainActivity.kt package com.example.mylibrary import android.content.Intent import android.os.Bundle import android.view.View import android.widget.Button import android.widget.TextView import androidx.appcompat.app.AppCompatActivity import androidx.recyclerview.widget.LinearLayoutManager import androidx.recyclerview.widget.RecyclerView class MainActivity : AppCompatActivity() { private lateinit var recyclerView : RecyclerView private lateinit var bookAdapter : BookAdapter private lateinit var emptyView : TextView override fun onCreate (savedInstanceState: Bundle?) { super .onCreate(savedInstanceState) setContentView(R.layout. activity_main ) recyclerView = findViewById(R.id. recyclerView ) recyclerView . layoutManager = LinearLayoutManager( this ) bookAdapter = BookAdapter(getAllBooksFromDatabase()) recyclerView . adapter = bookAdapter checkEmptyViewVisibility() // val dbHelper = DatabaseHelper(this, "BookStore.db", 2) // val createDatabase = findViewById<Button>(R.id.createDatabase) // createDatabase.setOnClickListener { // dbHelper.writableDatabase // } val addData = findViewById<Button>(R.id. addData ) addData.setOnClickListener { val intent = Intent( this @MainActivity , AddBookActivity:: class . java ) startActivity(intent) } } private fun getAllBooksFromDatabase (): List<Book> { val dbHelper = DatabaseHelper( this, "BookStore.db" , 2 ) val db = dbHelper. readableDatabase val query = "SELECT * FROM Book" val cursor = db.rawQuery(query , null ) val books = mutableListOf <Book>() while (cursor.moveToNext()) { val nameIndex = cursor.getColumnIndex( "name" ) val authorIndex = cursor.getColumnIndex( "author" ) val priceIndex = cursor.getColumnIndex( "price" ) val categoryIdIndex = cursor.getColumnIndex( "categoryId" ) val name: String? = cursor.getString(nameIndex) val author: String? = cursor.getString(authorIndex) val price: Double = cursor.getDouble(priceIndex) val categoryId: Int = cursor.getInt(categoryIdIndex) // 使用空字符串作为默认值 val book = Book(author ?: "" , price , 0 , name ?: "" , categoryId) books.add(book) } cursor.close() return books } private fun checkEmptyViewVisibility () { emptyView = findViewById(R.id. emptyTextView ) if ( bookAdapter . itemCount == 0 ) { emptyView . visibility = View. VISIBLE } else { emptyView . visibility = View. GONE } } } activity_main.xml <? xml version ="1.0" encoding ="utf-8" ?> <LinearLayout xmlns: android ="http://schemas.android.com/apk/res/android" android :orientation ="vertical" android :layout_width ="match_parent" android :layout_height ="match_parent" > <androidx.recyclerview.widget.RecyclerView android :id ="@+id/recyclerView" android :layout_width ="match_parent" android :layout_height ="wrap_content" android :layout_weight ="1" android :scrollbars ="vertical" /> <TextView android :id ="@+id/emptyTextView" android :layout_width ="match_parent" android :layout_height ="wrap_content" android :gravity ="center" android :visibility ="gone" android :text ="No books available" android :textSize ="20sp" />      <Button android :id ="@+id/addData" android :layout_width ="match_parent" android :layout_height ="wrap_content" android :text ="Add Book" />                 15     </LinearLayout> DataBaseHelper.kt package com.example.mylibrary import android.content.ContentValues import android.content.Context import android.database.sqlite.SQLiteDatabase import android.database.sqlite.SQLiteOpenHelper import android.widget.Toast class DatabaseHelper(context: Context , name: String , version: Int) : SQLiteOpenHelper(context , name , null, version) { private val createBook = "create table Book (" + "id integer primary key autoincrement," + "author text," + "price real," + "pages integer," + "name text," + "categoryId integer)" private val createCategory = "create table Category (" + "id integer primary key autoincrement," + "category_name text," + "category_code integer)" override fun onCreate (db: SQLiteDatabase) { db.execSQL( createBook ) db.execSQL( createCategory ) // Toast.makeText(this@DatabaseHelper, "Tables created successfully", Toast.LENGTH_SHORT).show() // 插入经济类别记录 val contentValues = ContentValues(). apply { put( "category_name" , " 经济类 " ) put( "category_code" , 1 ) } 16 db.insert( "Category" , null, contentValues) } override fun onUpgrade (db: SQLiteDatabase , oldVersion: Int , newVersion: Int) { db.execSQL( "DROP TABLE IF EXISTS Book" ) db.execSQL( "DROP TABLE IF EXISTS Category" ) onCreate(db) } } AddBookActivity.kt package com.example.mylibrary import android.content.ContentValues import android.content.Intent import android.os.Bundle import android.widget.Button import android.widget.EditText import android.widget.Toast import androidx.appcompat.app.AppCompatActivity class AddBookActivity : AppCompatActivity() { // private lateinit var dbHelper: DatabaseHelper override fun onCreate (savedInstanceState: Bundle?) { super .onCreate(savedInstanceState) setContentView(R.layout. activity_add_book ) // dbHelper = DatabaseHelper(this) val dbHelper =DatabaseHelper( this, "BookStore.db" , 2 ) val addBookButton: Button = findViewById(R.id. addBookButton ) addBookButton.setOnClickListener { val nameEditText: EditText = findViewById(R.id. nameEditText ) val authorEditText: EditText = findViewById(R.id. authorEditText ) // val category: EditText = findViewById(R.id.categoryIdEditText) val priceEditText: EditText = findViewById(R.id. priceEditText ) val categoryIdEditText: EditText = findViewById(R.id. categoryIdEditText ) val name = nameEditText. text .toString() val author = authorEditText. text .toString() 17 // val pages = pagesEditText.text.toString().toIntOrNull() ?: 0 // 处理无效输入 val price = priceEditText. text .toString(). toDoubleOrNull () ?: 0.0 // 处理无效输入 val categoryId = categoryIdEditText. text .toString(). toIntOrNull () ?: 0 // 处理无效输入 val db = dbHelper. writableDatabase val values = ContentValues(). apply { put( "name" , name) put( "author" , author) put( "categoryId" , categoryId) put( "price" , price) // put("categoryId", categoryId) } val newRowId = db.insert( "Book" , null, values) if (newRowId == - 1L ) { // 插入失败 Toast.makeText( this, " 添加书籍到数据库失败 " , Toast. LENGTH_SHORT ).show() } else { // 插入成功 Toast.makeText( this, " 书籍已添加到数据库 " , Toast. LENGTH_SHORT ).show() } // 清空输入框 nameEditText. text .clear() authorEditText. text .clear() categoryIdEditText. text .clear() priceEditText. text .clear() // categoryIdEditText.text.clear() val intent = Intent( this @AddBookActivity , MainActivity:: class . java ) startActivity(intent) // finish(); } } } activity_add_book.xml <? xml version ="1.0" encoding ="utf-8" ?> <RelativeLayout xmlns: android ="http://schemas.android.com/apk/res/android" android :layout_width ="match_parent" android :layout_height ="match_parent" android :padding ="16dp" > <EditText android :id ="@+id/authorEditText" android :layout_width ="match_parent" android :layout_height ="wrap_content" android :hint ="Author" android :layout_marginBottom ="16dp" android :minWidth ="200dp" android :minHeight ="48dp" android :padding ="8dp" /> <EditText android :id ="@+id/priceEditText" android :layout_width ="match_parent" android :layout_height ="wrap_content" android :inputType ="numberDecimal" android :hint ="Price" android :layout_below ="@id/authorEditText" android :layout_marginBottom ="16dp" android :minWidth ="200dp" android :minHeight ="48dp" android :padding ="8dp" /> <EditText android :id ="@+id/pagesEditText" android :layout_width ="match_parent" android :layout_height ="wrap_content" android :inputType ="number" android :hint ="Pages" android :layout_below ="@id/priceEditText" android :layout_marginBottom ="16dp" android :minWidth ="200dp" android :minHeight ="48dp" android :padding ="8dp" /> <EditText android :id ="@+id/nameEditText" android :layout_width ="match_parent" android :layout_height ="wrap_content" 18 android :hint ="Name" android :layout_below ="@id/pagesEditText" android :layout_marginBottom ="16dp" android :minWidth ="200dp" android :minHeight ="48dp" android :padding ="8dp" /> <EditText android :id ="@+id/categoryIdEditText" android :layout_width ="match_parent" android :layout_height ="wrap_content" android :inputType ="number" android :hint ="Category ID" android :layout_below ="@id/nameEditText" android :layout_marginBottom ="16dp" android :minWidth ="200dp" android :minHeight ="48dp" android :padding ="8dp" /> <Button android :id ="@+id/addBookButton" android :layout_width ="wrap_content" android :layout_height ="wrap_content" android :text ="Add Book" android :layout_centerInParent ="true" /> <androidx.recyclerview.widget.RecyclerView android :id ="@+id/recyclerView" android :layout_width ="match_parent" android :layout_height ="match_parent" android :layout_above ="@id/addBookButton" android :layout_marginBottom ="16dp" /> </RelativeLayout> BookAdapter.kt // BookAdapter.kt package com.example.mylibrary import android.view.LayoutInflater import android.view.View import android.view.ViewGroup import android.widget.TextView import androidx.recyclerview.widget.RecyclerView class BookAdapter( private val bookList : List<Book>) : RecyclerView.Adapter<BookAdapter.BookViewHolder>() { class BookViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) { val titleTextView : TextView = itemView.findViewById(R.id. textViewTitle ) val authorTextView : TextView = itemView.findViewById(R.id. textViewAuthor ) val categoryTextView : TextView = itemView.findViewById(R.id. textViewCategory ) val priceTextView : TextView = itemView.findViewById(R.id. textViewPrice ) } override fun onCreateViewHolder (parent: ViewGroup , viewType: Int): BookViewHolder { val itemView = LayoutInflater.from(parent. context ) .inflate(R.layout. item_book , parent , false ) return BookViewHolder(itemView) } override fun onBindViewHolder (holder: BookViewHolder , position: Int) { val currentItem = bookList [position] holder. titleTextView . text = currentItem. name holder. authorTextView . text = currentItem. author holder. categoryTextView . text = currentItem. categoryId .toString() holder. priceTextView . text = currentItem. price .toString() } override fun getItemCount () = bookList . size } item_book,xml <? xml version ="1.0" encoding ="utf-8" ?> <LinearLayout xmlns: android ="http://schemas.android.com/apk/res/android" android :layout_width ="match_parent" android :layout_height ="wrap_content" android :orientation ="vertical" > <TextView android :id ="@+id/textViewTitle" android :layout_width ="wrap_content" android :layout_height ="wrap_content" android :textSize ="18sp" android :textStyle ="bold" android :text ="Title" /> <TextView android :id ="@+id/textViewAuthor" android :layout_width ="wrap_content" android :layout_height ="wrap_content" android :textSize ="16sp" android :text ="Author" /> <TextView android :id ="@+id/textViewCategory" android :layout_width ="wrap_content" android :layout_height ="wrap_content" android :textSize ="14sp" android :text ="Category" /> <TextView android :id ="@+id/textViewPrice" android :layout_width ="wrap_content" android :layout_height ="wrap_content" android :textSize ="14sp" android :text ="Price" /> </LinearLayout>

标签：findViewById,持久,val,text,技术,id,import,Android,android
From： https://blog.csdn.net/2201_75709573/article/details/140880339

1. 用户登陆界面

2. 图书信息数据库和显示界面

3.应用运行功能的截图

4.源码

相关文章

赞助商

阅读排行