Room的使用

1. 添加插件
2. 添加依赖

   implementation "androidx.room:room-runtime:2.3.0"
   kapt "androidx.room:room-compiler:2.3.0"
              

3. 布局

   

   <?xml version="1.0" encoding="utf-8"?>
   <androidx.constraintlayout.widget.ConstraintLayout 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">
   
       <EditText
           android:id="@+id/salary_edit"
           android:layout_width="wrap_content"
           android:layout_height="wrap_content"
           android:ems="10"
           android:inputType="numberDecimal"
           app:layout_constraintBaseline_toBaselineOf="@+id/salary_text"
           app:layout_constraintEnd_toEndOf="parent"
           app:layout_constraintHorizontal_bias="0.0"
           app:layout_constraintStart_toStartOf="@+id/guideline3" />
   
       <Button
           android:id="@+id/add_user_button"
           android:layout_width="wrap_content"
           android:layout_height="wrap_content"
           android:text="添加用户"
           app:layout_constraintBottom_toBottomOf="parent"
           app:layout_constraintHorizontal_bias="0.498"
           app:layout_constraintLeft_toLeftOf="parent"
           app:layout_constraintRight_toRightOf="parent"
           app:layout_constraintTop_toBottomOf="@+id/salary_edit"
           app:layout_constraintVertical_bias="0.051" />
   
       <TextView
           android:id="@+id/name_text"
           android:layout_width="wrap_content"
           android:layout_height="wrap_content"
           android:text="请输入名称："
           app:layout_constraintBottom_toBottomOf="parent"
           app:layout_constraintEnd_toEndOf="@+id/age_text"
           app:layout_constraintEnd_toStartOf="@+id/guideline2"
           app:layout_constraintTop_toTopOf="parent"
           app:layout_constraintVertical_bias="0.11" />
   
       <androidx.constraintlayout.widget.Guideline
           android:id="@+id/guideline2"
           android:layout_width="wrap_content"
           android:layout_height="wrap_content"
           android:orientation="vertical"
           app:layout_constraintGuide_begin="123dp" />
   
       <TextView
           android:id="@+id/age_text"
           android:layout_width="wrap_content"
           android:layout_height="wrap_content"
           android:text="请输入年龄："
           app:layout_constraintBottom_toBottomOf="parent"
           app:layout_constraintEnd_toStartOf="@+id/guideline2"
           app:layout_constraintTop_toBottomOf="@+id/name_text"
           app:layout_constraintVertical_bias="0.058" />
   
       <TextView
           android:id="@+id/salary_text"
           android:layout_width="wrap_content"
           android:layout_height="wrap_content"
           android:layout_marginStart="72dp"
           android:text="请输入薪水："
           app:layout_constraintBottom_toBottomOf="parent"
           app:layout_constraintEnd_toStartOf="@+id/guideline2"
           app:layout_constraintHorizontal_bias="1.0"
           app:layout_constraintStart_toStartOf="parent"
           app:layout_constraintTop_toBottomOf="@+id/age_text"
           app:layout_constraintVertical_bias="0.066" />
   
       <androidx.constraintlayout.widget.Guideline
           android:id="@+id/guideline3"
           android:layout_width="wrap_content"
           android:layout_height="wrap_content"
           android:orientation="vertical"
           app:layout_constraintGuide_begin="132dp" />
   
       <EditText
           android:id="@+id/name_edit"
           android:layout_width="wrap_content"
           android:layout_height="wrap_content"
           android:ems="10"
           android:inputType="textPersonName"
           app:layout_constraintBaseline_toBaselineOf="@+id/name_text"
           app:layout_constraintEnd_toEndOf="parent"
           app:layout_constraintHorizontal_bias="0.0"
           app:layout_constraintStart_toStartOf="@+id/guideline3" />
   
       <EditText
           android:id="@+id/age_edit"
           android:layout_width="wrap_content"
           android:layout_height="wrap_content"
           android:ems="10"
           android:inputType="number"
           app:layout_constraintBaseline_toBaselineOf="@+id/age_text"
           app:layout_constraintEnd_toEndOf="parent"
           app:layout_constraintHorizontal_bias="0.0"
           app:layout_constraintStart_toStartOf="@+id/guideline3" />
   
       <Button
           android:id="@+id/query_user_button"
           android:layout_width="wrap_content"
           android:layout_height="wrap_content"
           android:text="查询用户"
           app:layout_constraintBottom_toBottomOf="parent"
           app:layout_constraintEnd_toEndOf="parent"
           app:layout_constraintHorizontal_bias="0.498"
           app:layout_constraintStart_toStartOf="parent"
           app:layout_constraintTop_toBottomOf="@+id/add_user_button"
           app:layout_constraintVertical_bias="0.021" />
   
       <ScrollView
           android:layout_width="match_parent"
           android:layout_height="wrap_content"
           app:layout_constraintBottom_toBottomOf="parent"
           app:layout_constraintEnd_toEndOf="parent"
           app:layout_constraintStart_toStartOf="parent"
           app:layout_constraintVertical_bias="0.04"
           app:layout_constraintTop_toBottomOf="@+id/query_user_button">
   
           <LinearLayout
               android:layout_width="match_parent"
               android:layout_height="wrap_content"
               android:orientation="vertical">
   
               <TextView
                   android:id="@+id/users_text"
                   android:layout_width="match_parent"
                   android:layout_height="wrap_content"/>
           </LinearLayout>
       </ScrollView>
   
   </androidx.constraintlayout.widget.ConstraintLayout>
              

4. 代码

   @Entity
   data class User(
       @PrimaryKey(autoGenerate = true)
       val uid: Int?,
   
       @ColumnInfo(name = "user_name")
       val name: String,
   
       val age: Int,
       val salary: Float
   )
              

   @Dao
   interface UserDao {	
       @Query("SELECT * FROM user")
       fun getAll(): List<User>
   
       @Query("SELECT * FROM user WHERE uid IN (:userIds)")
       fun loadAllByIds(userIds: IntArray): List<User>
   
       @Query("SELECT * FROM user WHERE user_name LIKE :name LIMIT 1")
       fun findByName(name: String): User
   
       @Insert
       fun insertAll(vararg users: User)
   
       @Delete
       fun delete(user: User)
   }
              

   @Database(entities = [User::class], version = 1)
   abstract class AppDatabase : RoomDatabase() {
       abstract fun userDao(): UserDao
   }
              

   class MainActivity : AppCompatActivity() {
   
       private lateinit var database: AppDatabase
       private lateinit var userDao: UserDao
   
       override fun onCreate(savedInstanceState: Bundle?) {
           super.onCreate(savedInstanceState)
           setContentView(R.layout.activity_main)
           findViewById<Button>(R.id.add_user_button).setOnClickListener(::addUser)
           findViewById<Button>(R.id.query_user_button).setOnClickListener(::queryUser)
   
           database = Room.databaseBuilder(applicationContext, AppDatabase::class.java, "mydb.sqlite").build()
           userDao = database.userDao()
   
       }
   
       fun addUser(view: View) {
           val name = findViewById<EditText>(R.id.name_edit).text.toString()
           val age = findViewById<EditText>(R.id.age_edit).text.toString().toInt()
           val salary = findViewById<EditText>(R.id.salary_edit).text.toString().toFloat()
           thread { userDao.insertAll(User(null, name, age, salary)) }
       }
   
       fun queryUser(view: View) {
           thread {
               val users = userDao.getAll()
               val sb = StringBuilder()
               users.forEach { sb.append(it).append('\n') }
               runOnUiThread {
                   findViewById<TextView>(R.id.users_text).text = sb
               }
           }
       }
   
       override fun onDestroy() {
           super.onDestroy()
           database.close()
       }
   }