7. 持久化技术

持久化技术可以让数据在瞬时状态和持久状态之间进行转换
- 文件存储
- SharedPreferences 存储
- 数据区存储

MainActivity2

package com.example.helloworld

import android.content.Context
import android.content.Intent
import android.os.Bundle
import android.util.Log
import android.widget.ArrayAdapter
import android.widget.Button
import android.widget.ListView
import androidx.appcompat.app.AppCompatActivity
import androidx.appcompat.widget.Toolbar


class MainActivity2 : BaseActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.second_layout)

        // toolbar 部分
        val toolbar: Toolbar = findViewById(R.id.toolbar2)
        setSupportActionBar(toolbar)
        supportActionBar?.setDisplayHomeAsUpEnabled(true)            // 设置返回按钮
        toolbar.setNavigationOnClickListener { finish() }             // 设置结束 act2

        ActivityCollector.addActivity(this)

        // 从前一个 Activity 接收数据
        val extraData1 = intent.getStringExtra("param1")
        val extraData2 = intent.getStringExtra("param2")
        Log.d("Activity2", "param1 is $extraData1, param2 is $extraData2")


        // 返回数据（但是未实现）
        val button2: Button = findViewById(R.id.button2)        // 通过 id 找到 view, 并指明类型为 button
        button2.setOnClickListener {
            val intent = Intent().apply { putExtra("data_return", "Hello Activity1") }
            setResult(RESULT_OK, intent)
            finish()
        }

        // 关闭所有 Activity
        val button3: Button = findViewById(R.id.button3)
        button3.setOnClickListener {
            ActivityCollector.finishAll()
        }

        val button4: Button = findViewById(R.id.button4)
        button4.setOnClickListener {
            startNewActivity(this, MainActivity3::class.java)
        }

        val button5: Button = findViewById(R.id.button5)
        button5.setOnClickListener {
            startNewActivity(this, MainActivity4::class.java)
        }

        val button7: Button = findViewById(R.id.button7)
        button7.setOnClickListener {
            startNewActivity(this, FragmentActivity::class.java)
        }
        val button8: Button = findViewById(R.id.button8)
        button8.setOnClickListener {
            startNewActivity(this, FileStorage::class.java)
        }

        val button9: Button = findViewById(R.id.button9)
        button9.setOnClickListener {
            startNewActivity(this, DataPreference::class.java)
        }

        val button10: Button = findViewById(R.id.button10)
        button10.setOnClickListener {
            startNewActivity(this, SqliteDB::class.java)
        }

    }

}

second_layout

<?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.appcompat.widget.Toolbar
        android:id="@+id/toolbar2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="?attr/colorPrimary"
        android:minHeight="?attr/actionBarSize"
        android:theme="?attr/actionBarTheme" />

    <Button
        android:id="@+id/button2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Back" />

    <Button
        android:id="@+id/button3"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Quit App" />

    <Button
        android:id="@+id/button4"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Go third" />

    <Button
        android:id="@+id/button5"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Go forth" />

    <Button
        android:id="@+id/button7"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Go Fragment" />

    <Button
        android:id="@+id/button8"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="File Storage" />

    <Button
        android:id="@+id/button9"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="SharedPreferences" />

    <Button
        android:id="@+id/button10"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="SQLite" />

</LinearLayout>

1. 文件存储

FileStorage

package com.example.helloworld

import android.content.Context
import android.os.Bundle
import android.widget.EditText
import android.widget.Toast
import java.io.BufferedReader
import java.io.BufferedWriter
import java.io.IOException
import java.io.InputStreamReader
import java.io.OutputStreamWriter

class FileStorage : BaseActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        // 设置 layout
        setContentView(R.layout.file_storage_layout)
        ActivityCollector.addActivity(this)

        val editText : EditText = findViewById(R.id.editText)
        val inputText = load()      // 启动时读取数据
        if (inputText.isNotEmpty()) {
            editText.setText(inputText)
            editText.setSelection(inputText.length)
            Toast.makeText(this, "Restoring succeeded", Toast.LENGTH_SHORT).show()
        }
    }

    override fun onDestroy() {      // 退出程序时自动保存字符串
        super.onDestroy()
        val editText : EditText = findViewById(R.id.editText)
        val inputText = editText.text.toString()
        save(inputText)
    }
    private fun save(inputText: String) {
        try {
            val output = openFileOutput("data", Context.MODE_PRIVATE)
            val writer = BufferedWriter(OutputStreamWriter(output))
            writer.use {
                it.write(inputText)
            }
        } catch (e: IOException) {
            e.printStackTrace()
        }
    }

    private fun load(): String {
        val content = StringBuilder()
        try {
            val input = openFileInput("data")
            val reader = BufferedReader(InputStreamReader(input))
            reader.use {
                reader.forEachLine {
                    content.append(it)
                }
            }
        } catch (e: IOException) {
            e.printStackTrace()
        }
        return content.toString()
    }
}

file_storage_layout

<?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" >

    <EditText
        android:id="@+id/editText"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Type something here"
        />

</LinearLayout>

2. SharedPreferences

DataPerference

package com.example.helloworld

import android.content.Context
import android.content.Intent
import android.os.Bundle
import android.widget.Button
import android.widget.CheckBox
import android.widget.EditText
import android.widget.Toast
import androidx.core.content.edit

class DataPreference : BaseActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.data_perference)

        val prefs = getPreferences(Context.MODE_PRIVATE)
        val isRemember = prefs.getBoolean("remember_password", false)
        val accountEdit: EditText = findViewById(R.id.accountEdit)
        val passwordEdit: EditText = findViewById(R.id.passwordEdit)
        val rememberPass: CheckBox = findViewById(R.id.rememberPass)
        val login: Button = findViewById(R.id.login)
        if (isRemember) {
            // 将账号和密码都设置到文本框中
            val account = prefs.getString("account", "")
            val password = prefs.getString("password", "")

            accountEdit.setText(account)
            passwordEdit.setText(password)
            rememberPass.isChecked = true
        }
        login.setOnClickListener {
            val account = accountEdit.text.toString()
            val password = passwordEdit.text.toString()
            // 如果账号是admin且密码是123456，就认为登录成功
            if (account == "admin" && password == "123456") {
                prefs.edit {
                    if (rememberPass.isChecked) { // 检查复选框是否被选中
                        putBoolean("remember_password", true)
                        putString("account", account)
                        putString("password", password)
                    } else {
                        clear()
                    }
                }
                val intent = Intent(this, MainActivity::class.java)
                startActivity(intent)
                finish()
            } else {
                Toast.makeText(this, "account or password is invalid",
                    Toast.LENGTH_SHORT).show()
            }
        }
    }

}

data_perference

<?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">
<LinearLayout
    android:orientation="horizontal"
    android:layout_width="match_parent"
    android:layout_height="60dp">
    <TextView
        android:layout_width="90dp"
        android:layout_height="wrap_content"
        android:layout_gravity="center_vertical"
        android:textSize="18sp"
        android:text="Account:" />
    <EditText
        android:id="@+id/accountEdit"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:layout_gravity="center_vertical" />
</LinearLayout>
<LinearLayout
    android:orientation="horizontal"
    android:layout_width="match_parent"
    android:layout_height="60dp">
    <TextView
        android:layout_width="90dp"
        android:layout_height="wrap_content"
        android:layout_gravity="center_vertical"
        android:textSize="18sp"
        android:text="Password:" />
    <EditText
        android:id="@+id/passwordEdit"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:layout_gravity="center_vertical"
        android:inputType="textPassword" />
</LinearLayout>
    <LinearLayout
        android:orientation="horizontal"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">
        <CheckBox
            android:id="@+id/rememberPass"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" />
        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textSize="18sp"
            android:text="Remember password" />
    </LinearLayout>
<Button
    android:id="@+id/login"
    android:layout_width="200dp"
    android:layout_height="60dp"
    android:layout_gravity="center_horizontal"
    android:text="Login" />
</LinearLayout>

3. SQLite

SqliteDB.kt

package com.example.helloworld

import android.content.ContentValues
import android.content.Context
import android.database.sqlite.SQLiteDatabase
import android.database.sqlite.SQLiteOpenHelper
import android.os.Bundle
import android.util.Log
import android.widget.Button
import android.widget.Toast


class MyDatabaseHelper(val 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," +
            "category_id 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)
    }

    override fun onUpgrade(db: SQLiteDatabase, oldVersion: Int, newVersion: Int) {
        if (oldVersion <= 1) {
            db.execSQL(createCategory)
        }
        if (oldVersion <= 2) {
            db.execSQL("alter table Book add column category_id integer")
        }
    }
}

class SqliteDB : BaseActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.sql_layout)
        ActivityCollector.addActivity(this)

        // 调用 helper 根据版本号创建或者升级数据库
        val dbHelper = MyDatabaseHelper(this, "BookStore.db", 2)
        val createDatabase: Button = findViewById(R.id.createDatabase)
        createDatabase.setOnClickListener {
            dbHelper.writableDatabase
        }

        // 添加数据
        val addData: Button = findViewById(R.id.addData)
        addData.setOnClickListener {
            val db = dbHelper.writableDatabase
            val values1 = ContentValues().apply {
                // 开始组装第一条数据
                put("name", "The Da Vinci Code")
                put("author", "Dan Brown")
                put("pages", 454)
                put("price", 16.96)
            }
            db.insert("Book", null, values1) // 插入第一条数据
            val values2 = ContentValues().apply {
                // 开始组装第二条数据
                put("name", "The Lost Symbol")
                put("author", "Dan Brown")
                put("pages", 510)
                put("price", 19.95)
            }
            db.insert("Book", null, values2) // 插入第二条数据
        }

        // 更新数据
        val updateData: Button = findViewById(R.id.updateData)
        updateData.setOnClickListener {
            val db = dbHelper.writableDatabase
            val values = ContentValues()
            values.put("price", 10.99)
            db.update("Book", values, "name = ?", arrayOf("The Da Vinci Code"))
        }

        // 删除数据
        val deleteData: Button = findViewById(R.id.deleteData)
        deleteData.setOnClickListener {
            val db = dbHelper.writableDatabase
            db.delete("Book", "pages > ?", arrayOf("500"))
        }

        // 查询数据
        val queryData: Button = findViewById(R.id.queryData)
        queryData.setOnClickListener {
            val db = dbHelper.writableDatabase
            // 查询Book表中所有的数据
            val cursor = db.query("Book", null, null, null, null, null, null)
            if (cursor.moveToFirst()) {
                do {
                    // 遍历Cursor对象，取出数据并打印
                    val name = cursor.getString(cursor.getColumnIndex("name"))
                    val author = cursor.getString(cursor.getColumnIndex("author"))
                    val pages = cursor.getInt(cursor.getColumnIndex("pages"))
                    val price = cursor.getDouble(cursor.getColumnIndex("price"))
                    Log.d("SqliteDB", "book name is $name")
                    Log.d("SqliteDB", "book author is $author")
                    Log.d("SqliteDB", "book pages is $pages")
                    Log.d("SqliteDB", "book price is $price")
                } while (cursor.moveToNext())
            }
            cursor.close()
        }

        // 使用事务确保原子性进行数据替换
        val replaceData: Button = findViewById(R.id.replaceData)
        replaceData.setOnClickListener {
            val db = dbHelper.writableDatabase
            db.beginTransaction() // 开启事务
            try {
                db.delete("Book", null, null)
                if (true) {
                    // 手动抛出一个异常，让事务失败
                    throw NullPointerException()
                }
                val values = ContentValues().apply {
                    put("name", "Game of Thrones")
                    put("author", "George Martin")
                    put("pages", 720)
                    put("price", 20.85)
                }
                db.insert("Book", null, values)
                db.setTransactionSuccessful() // 事务已经执行成功
            } catch (e: Exception) {
                e.printStackTrace()
            } finally {
                db.endTransaction() // 结束事务
            }
        }
    }
}

sql_layout

<?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"
    >

    <Button
        android:id="@+id/createDatabase"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Create Database"
        />

    <Button
        android:id="@+id/addData"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Add Data"
        />

    <Button
        android:id="@+id/updateData"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Update Data"
        />

    <Button
        android:id="@+id/deleteData"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Delete Data"
        />

    <Button
        android:id="@+id/queryData"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Query Data"
        />

    <Button
        android:id="@+id/replaceData"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Replace Data"
        />
</LinearLayout>

// 添加数据
db.execSQL("insert into Book (name, author, pages, price) values(?, ?, ?, ?)", 
    arrayOf("The Da Vinci Code", "Dan Brown", "454", "16.96") 
) 
db.execSQL("insert into Book (name, author, pages, price) values(?, ?, ?, ?)", 
    arrayOf("The Lost Symbol", "Dan Brown", "510", "19.95") 
)
// 更新数据
db.execSQL("update Book set price = ? where name = ?", arrayOf("10.99", "The Da Vinci Code"))
// 删除数据
db.execSQL("delete from Book where pages > ?", arrayOf("500")) 
// 查询数据
val cursor = db.rawQuery("select * from Book", null)

posted @ 2026-01-14 17:42 y丶innocence 阅读(4) 评论(0) 收藏举报

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y丶innocence

7. 持久化技术

7. 持久化技术

1. 文件存储

2. SharedPreferences

3. SQLite

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