Android Weekly Issue #428

Kotlin Flow Retry Operator with Exponential Backoff Delay

這是講協程Flow系列文章中的一篇.

對于重試的兩個運算子:

retryWhen
retry

retryWhen的使用:

.retryWhen { cause, attempt ->
    if (cause is IOException && attempt < 3) {
        delay(2000)
        return@retryWhen true
    } else {
        return@retryWhen false
    }
}

retry:

.retry(retries = 3) { cause ->
    if (cause is IOException) {
        delay(2000)
        return@retry true
    } else {
        return@retry false
    }
}

可以把時間指數延長:

viewModelScope.launch {
    var currentDelay = 1000L
    val delayFactor = 2
    doLongRunningTask()
        .flowOn(Dispatchers.Default)
        .retry(retries = 3) { cause ->
            if (cause is IOException) {
                delay(currentDelay)
                currentDelay = (currentDelay * delayFactor)
                return@retry true
            } else {
                return@retry false
            }
        }
        .catch {
            // error
        }
        .collect {
            // success
        }
}

Fragments: Rebuilding the Internals

Fragment在Android 10已經廢棄, 現在不在framework中了, 只在AndroidX中有.

這個Fragment 1.3.0-alpha08版本的發布, 有一些關于FragmentManager內部狀態的重要更新.
解決了很多issue, 簡化了fragment的生命周期, 還提供了一個FragmentManager多個back stacks的支持.

核心就是這個FragmentStateManager類.

這個FragmentStateManager負責:

轉換Fragment的生命周期狀態.
跑影片和轉場.
處理延遲轉換.

Postponed fragments

關于狀態的確定, 有一個case是一個難點: postponed fragments.
這是一個以前就有的東西, 通常跟shared element transition影片有關系.

postponed fragment有兩個特點:

view創建了, 但是不可見.
lifecycle頂多到STARTED.

只有呼叫這個方法: startPostponedEnterTransition()之后, fragment的transition才會跑, view會變成可見, fragment會移動到RESUMED.

所以有這個bug: Postponed Fragments leave the Fragments and FragmentManager in an inconsistent state bug.

這個issue相關聯的還有好幾個issues.

在容器層面解決問題

用一個SpecialEffectsController(以后名字可能會改)來處理所有影片轉場相關的東西.

這樣FragmentManager就被解放出來, 不需要處理postponed的邏輯, 而是交給了container, 這樣就避免了FragmentManager中狀態不一致的問題.

新的StateManager構架

原先: 一個FragmentManager總管所有.

現在: FragmentManager和各個FragmentStateManager的實體交流.

The FragmentManager only has state that applies to all fragments.
The FragmentStateManager manages the state at the fragment level.
The SpecialEffectsController manages the state at the container level.

總體

這個改動新發布, 實驗階段, 總體來說是應該沒有行為改變的.

如果有行為改變, 對你的程式造成了影響, 也可以暫時關閉(FragmentManager.enableNewStateManager(false)), 并且報告個issue.

A Framework For Speedy and Scalable Development Of Android UI Tests

講了一整套的測驗實踐.

沒有用Appium, 用的UI Automator和Espresso.

Basic Coroutine Level 1

Kotlin協程的概念.

Android Lint Framework — An Introduction

Android Lint的介紹.

創建一個Lint規則, 保證每個人都用專案自定義的ImageView, 而不是原生的ImageView.

具體做法:

首先從創建一個叫做custom-lint的module. 需要依賴lint-api和lint-checks:

compileOnly "com.android.tools.lint:lint-api:$androidToolsVersion"
compileOnly "com.android.tools.lint:lint-checks:$androidToolsVersion"

這里用了compileOnly是因為不想lint API在runtime available.

之后創建自定義規則. 每個lint check的實作都叫一個detector. 需要繼承Detector, 并且利用Scanners來做掃描. 報告錯誤需要定義Issue. 還可以創建LintFx, 作為quick fix.

class ImageViewUsageDetector : LayoutDetector() {
  
   // Applicable elements
  
  
    override fun visitElement(context: XmlContext, element: Element) {
        context.report(
            issue = ISSUE, 
            location = context.getElementLocation(element), 
            message = REPORT_MESSAGE, 
            quickfixData = https://www.cnblogs.com/mengdd/archive/2020/08/31/computeQuickFix() 
        )
    }

   
    private fun computeQuickFix(): LintFix {
        return LintFix.create()
            .replace().text(SdkConstants.IMAGE_VIEW)
            .with(TINTED_IMAGE_VIEW)
            .build()
    }

  // Issue, implementation, and other constants 

}

然后把定義好的自定義規則注冊.

class Registry: IssueRegistry() {

    override val issues: List<Issue>
        get() = listOf(ImageViewUsageDetector.ISSUE)

    override val api: Int = CURRENT_API

}

創建入口, 在build.gradle檔案中:


// Configure jar to register our lint registry
jar {
    manifest {
        attributes("Lint-Registry-v2": "com.tintedimagelint.lint.Registry")
    }
}

加上依賴和一些配置.


android {
    
    // Configurations above
    lintOptions {
        lintConfig file('../analysis/lint/lint.xml')
        htmlOutput file("$project.buildDir/reports/lint/lint-reports.html")
        xmlOutput file("$project.buildDir/reports/lint/lint-reports.xml")
        abortOnError false
    }
    //Configurations below
}

dependencies {
    // Dependencies above

    // Include custom lint module as a lintCheck
    lintChecks project(":custom-lint")

    // Dependencies below
}

Codelabs for new Android game technologies

關于Android Game新技術的Codelabs:

資源打包: Play Asset Delivery -> https://codelabs.developers.google.com/codelabs/unity-gamepad/#0
幀率和影像: Android Performance Tuner -> https://codelabs.developers.google.com/codelabs/android-performance-tuner-unity/#0

都是Unity的game.

Android Vitals - When did my app start?

系列文章之六, 我的app啥時候啟動的?

看個結論吧:

Here's how we can most accurately measure the app start time when monitoring cold start:

Up to API 24: Use the class load time of a content provider.
API 24 - API 28: Use Process.getStartUptimeMillis().
API 28 and beyond: Use Process.getStartUptimeMillis() but filter out weird values (e.g. more than 1 min to get to Application.onCreate()) and fallback to the time ContentProvider.onCreate() is called.

Comparing Three Dependency Injection Solutions

比較三種依賴注入的解決方案.

手寫方式.
Koin.
Dagger Hilt.

Avoiding memory leaks when using Data Binding and View Binding

使用Data Binding和View Binding的時候, 注意記憶體泄漏問題.

Google建議在Fragment中使用binding時, 要在onDestroyView中置為null:

private var _binding: ResultProfileBinding? = null
// This property is only valid between onCreateView and
// onDestroyView.
private val binding get() = _binding!!

override fun onCreateView(
    inflater: LayoutInflater,
    container: ViewGroup?,
    savedInstanceState: Bundle?
): View? {
    _binding = ResultProfileBinding.inflate(inflater, container, false)
    val view = binding.root
    return view
}

override fun onDestroyView() {
    super.onDestroyView()
    _binding = null
}

有個博客中介紹的方法, 可以簡化成這樣:

private val binding: FragmentFirstBinding by viewBinding()

Fragment還有一個引數的構造, 可以傳入布局id:

class FirstFragment : Fragment(R.layout.fragment_first) {

  private val binding: FragmentFirstBinding by viewBinding()
  
  override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
      super.onViewCreated(view, savedInstanceState)
      // Any code we used to do in onCreateView can go here instead
  }
}

冷知識: DataBinding實作了ViewBinding.

public abstract class ViewDataBinding extends BaseObservable implements ViewBinding

所以ViewBinding和DataBinding方法通用.

Anti-patterns of automated software testing

關于測驗的一些anti-patterns.

Using bytecode analysis to find unused dependencies

關于這個庫: https://github.com/autonomousapps/dependency-analysis-android-gradle-plugin的說明.

Code

https://github.com/jmfayard/refreshVersions: 一個依賴版本管理的gradle插件.

后記

好久沒在博客園發過這個系列.
其實一直還有在更, 只不過寫得比較散亂隨意, 所以丟在了簡書:
https://www.jianshu.com/c/e51d4d597637

最近有點忙, 不太有時間寫博客, 積攢了好多話題都是沒有完成的.
看博客兩個月沒更了, 拿這篇刷一下存在感.
是想多寫點真正厲害有價值的原創的.
先韜光養晦, 積累一下.

轉載請註明出處，本文鏈接：https://www.uj5u.com/yidong/106767.html

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Android Weekly Notes Issue #428