Android Weekly Issue #439

How to Make the Compiler Smarter

Contract:

fun foo(): Boolean {
    contract {
        // Effect
    }
    // Function body
}

可以用如下几种方法:

• returns(value)
• returnsNotNull()
• implies(booleanExpression)
• callsInPlace(lambda, kind)

Mastering API Visibility in Kotlin

在设计API的时候, 暴露的越少越好.

目的:

• Easier to maintain and change.
• Easier to learn.
• Harder to misuse.

internal关键字标明模块内可见, 设计library的时候很有用.

测试的时候可以这样用:

@VisibleForTesting(otherwise = PRIVATE)
internal var state: State

kotlin的internal对于Java来说其实是public. 但是用起来名字会比较古怪, 比如 an internal method called createEntity will become something like createEntity$moduleName (on Android, it’s also suffixed by the build variant in addition to the module name).

解决的方法可以有:

class Repository {
    @JvmName("pleaseDoNotCallThisMethod")
    internal fun createEntity() { ... }
}

或者:

class Repository {
    @JvmSynthetic
    internal fun createEntity() { ... }
}

因为Kotlin默认都是public的, 所以很容易忘了限制, Kotlin1.4开始有了Explicit API mode
强制给所有的声明都加上访问限定符.

有一个问题是public inline方法不能调用internal的方法.
解决的办法就是加上@PublishedApi注解:

@PublishedApi
internal fun secretFunction() {
    println("through the mountains")
}

public inline fun song() {
    secretFunction()
}
fun clientCode() {
    song() // ok
    secretFunction() // e: Cannot access 'secretFunction': it is internal
}

可能你的库有多个module, 而你又不想暴露给外部世界core之类的module, 那么就要用到opt-in.

Full Text Search in Room Tutorial: Getting Started

Room数据库中的全文搜索.

View binding for the lazy

Kotlin delegation + view binding.

还有另一个文章讲View Binding的好处: 3 Major Benefits Of View Binding Android

Android library development - Modularization

SDK库开发的模块化.

Code

• Bundler Bundle相关的Extensions.
• Barista 让Espresso UI测试更好写.
• AffectedModuleDetector 显示出受影响的modules.