Android Weekly Issue #483

Hands on Jetpack AppSearch

Android 12的新feature: App Search.

MAD Skills series: Hilt under the hood

在Hilt中, 三个最重要的注解:

@AndroidEntryPoint.
@InstallIn.
@HiltAndroidApp.

解释hilt是如何工作的.

对多个module的Classpath aggregation有图片说明.

Effective Kotlin Item 49: Consider using inline value classes

Kotlin 1.3是inline class, 1.5改为value class, 作为更大的功能点.

inline class Name(private val value: String) {
    // ...
}

这段代码编译后变为:

// Code
val name: Name = Name("Marcin")

// During compilation replaced with code similar to:
val name: String = "Marcin"

方法都会被作为静态方法:

@JvmInline
value class Name(private val value: String) {
    // ...

    fun greet() {
        print("Hello, I am $value")
    }
}

// Code
val name: Name = Name("Marcin")
name.greet()

// During compilation replaced with code similar to:
val name: String = "Marcin"
Name.`greet-impl`(name)

两种流行的使用场景:

To indicate a unit of measure. 测量单位. 举例: 时间单位.

@JvmInline
value class Minutes(val minutes: Int) {
    fun toMillis(): Millis = Millis(minutes * 60 * 1000)
    // ...
}

@JvmInline
value class Millis(val milliseconds: Int) {
    // ...
}

interface User {
    fun decideAboutTime(): Minutes
    fun wakeUp()
}

interface Timer {
    fun callAfter(timeMillis: Millis, callback: () -> Unit)
}

fun setUpUserWakeUpUser(user: User, timer: Timer) {
    val time: Minutes = user.decideAboutTime()
    timer.callAfter(time) { // ERROR: Type mismatch
        user.wakeUp()
    }
}

这样就不会搞混. 强制我们使用正确的单位.

我们可以定义这样的extension properties:

inline val Int.min 
    get() = Minutes(this)

inline val Int.ms 
    get() = Millis(this)

val timeMin: Minutes = 10.min

To use types to protect user from value misuse.
使用场景, 把id包装在inline class里:

@JvmInline
value class StudentId(val studentId: Int)

@JvmInline
value class TeacherId(val teacherId: Int)

@JvmInline
value class SchoolId(val studentId: Int)

@Entity(tableName = "grades")
class Grades(
   @ColumnInfo(name = "studentId") 
   val studentId: StudentId,
   @ColumnInfo(name = "teacherId") 
   val teacherId: TeacherId,
   @ColumnInfo(name = "schoolId") 
   val schoolId: SchoolId,
    // ...
)

需要注意的是当inline class实现了接口或者接受可空参数以后, 它就不被inline了.

Testing Hybrid Jetpack Compose Apps

View和Compose混合应用的UI测试.

Thinking functionally in Kotlin

函数式: 基本的积木块是函数.

举的例子: 判断一个点是否在射程以内.

A Simple Framework For Mobile System Design Interviews

mobile开发面试.

面试流程和每个环节的设计.

Utilizing ADB for daily tasks

日常使用adb.

自动填写两个字段实现登录:

adb shell input text user1 && adb shell input tap x y && adb shell input text password1 && adb shell input tap x y

截图:

adb shell screencap $PATH_IN_DEVICE

录屏:

adb shell screenrecord $PATH_IN_DEVICE

测试deep link:

adb shell am start
        -W -a android.intent.action.VIEW
        -d  
        
adb shell am start
        -W -a android.intent.action.VIEW
        -d "example://gizmos" com.example.android

Jetpack Compose Side-Effects II — rememberCoroutineScope

LaunchedEffect可以在composable内部启动一个协程. 并且在composition退出时清理.

LaunchedEffect的一些限制:

LaunchedEffect是一个composable, 它只能在composable方法里调用.
用LaunchedEffect, 你不能控制coroutine的生命周期.

对于这样的场景, 我们有rememberCoroutineScope.

rememberCoroutineScope是一个返回scope的方法, 在composable中调用, 在composable离开composition的时候自动取消.

利用它我们就可以在callback里做事情.

我们还可以手动取消.

Trackr comes to the Big Screen

一个任务管理应用的大屏适配.

导航: navigation-rail
List-Detail: SlidingPaneLayout
Edit: Dialog.

Code: https://github.com/android/trackr

Don't mock static: test Timber Logger with trees

如何测试log.

import timber.log.Timber

class TestTree : Timber.Tree() {
  val logs = mutableListOf()

  override fun log(priority: Int, tag: String?, message: String, t: Throwable?) {
    logs.add(Log(priority, tag, message, t))
  }

  data class Log(val priority: Int, val tag: String?, val message: String, val t: Throwable?)
}

加上这个辅助方法:

fun withTestTree(body: TestTree.() -> Unit) {
  val testTree = TestTree()
  Timber.plant(testTree)
  body(testTree)
  Timber.uproot(testTree)
}

最后是这样:

"given service error when get all called then log warn" {

  //setup system under test
  withTestTree {
    val service = mockk {
      every { getAll() } throws Exception("Something failed :(")
    }
    val systemUnderTest = SystemUnderTest(service)

    //execute system under test
    systemUnderTest.fetchData()

    //capture last logged event
    val lastLoggedEvent = logs.last()

    assertSoftly {
      lastLoggedEvent.message shouldContain "fetchData returned exception instead of empty list"
      lastLoggedEvent.priority shouldBe Log.WARN
    }
  }
}

文章所在的这个网站叫Kotlin Testing

Mocking Matchers API

mock library, 作者用的是mockito-kotlin

这个方法:

val product = mock {
    on { calculatePrice(any())} doAnswer  { i ->
        when (val discountId = i.getArgument(0)) {
            null -> Price(10)
            discountId1 -> Price(5)
            discountId2 -> Price(4)
            else -> throw UnsupportedOperationException("$discountId is not mocked")
        }
    }
}

传null的时候并不生效, 因为应该用anyOrNull而不是any.

然后作者对Mockito, mockito-kotlin, 和 mockk的argument matcher进行了比较.

MockWebServer + HTTPS

MockWebServer的配置问题.

用到了: okhttp-tls

Code

https://rbusarow.github.io/Tangle/ 一个依赖注入的工具.

News

Accelerated Kotlin build times with Kotlin Symbol Processing 1.0
已经支持moshi和room了: https://github.com/google/ksp#supported-libraries
Kotlin premier event

Android Weekly Notes #483