Kotlin Basic Learning - series 6

2018-04-20 本文已影响53人 swust_cp

Google推送的31天快速了解Kotlin，这篇就是最后一个了。但我还会继续从平时的学习中分享一些有用的学习经历

Android KTX提供了bundle creator，可以让我们在创建bundle的时候更加简洁，不用再调用'putString', 'putInt'等方法，调用一次就返回一个新bundle
```
val bundle = bundleOf(
     "KEY_INT" to 1, 
     "KEY_LONG" to 2L,
     "KEY_BOOLEAN" to true,
     "KEY_NULL" to null,
     "KEY_ARRAY" to arrayOf(1, 2)
 )
```
android/android-ktxandroid-ktx - A set of Kotlin extensions for Android app development.github.com
当我们最后一个参数是回调的时候，你可以通过Lambda来cleanup callbacks，Callable以及Runnable。比如，Android KTX提供了‘postDelayed’ with Lambda。
```
// Android KTX API
fun Handler.postDelayed(delay: Int /* ... */, action: ()-> Unit)

// Call it like this - no need for a Runnable in your code
handler.postDelayed(50) {
 // pass a lambda to postDelayed
}
```
android/android-ktxandroid-ktx - A set of Kotlin extensions for Android app development.github.com

Kotlin KTX给一些最常用的spans添加了extension，这样可以让其相关的API更加使用起来更简单。

var string = buildSpannedString {
    append("no styling text")
    bold {
        append("bold")
        italic {
            append("bold and italic")
        }
    }
    inSpans(RelativeSizeSpan(2f), QuoteSpan()) {
        append("double sized quote text")
    }
}

android/android-ktxandroid-ktx - A set of Kotlin extensions for Android app development.github.com

Kotlin提供了Parcelize可以让你实现Parcelable的时候更加的简洁

@Parcelize
data class User(val name: String, val occupation: Work): Parcelable

// build.gradle
androidExtensions {
    // Enable experimental Kotlin features in gradle to enable Parcelize
    experimental = true
}

Kotlin/KEEPKotlin Evolution and Enhancement Process. Contribute to KEEP development by creating an…github.com

通过使用default的参数列表来扩展现有函数API。Android KTX可以让你设置任意的一个参数。

view.updatePadding(left = newPadding)
view.updatePadding(top = newPadding)
view.updatePadding(right = newPadding)
view.updatePadding(bottom = newPadding)

view.updatePadding(top = newPadding, bottom = newPadding)

android/android-ktxandroid-ktx - A set of Kotlin extensions for Android app development.github.com

'let', 'apply', 'with'和‘run’都有一个receiver(this), 可能有一个argument(it)以及可能有一个返回值，下面来看一下它们的区别：

val string = "a"
val result = string.run {
    // this = "a"
    // it = not available
    1 // Block return value
    // result = 1
}

val string = "a"
val result = string.let {
    // this = this@MyClass
    // it = "a"
    2 // Block return value
    // result = 2
}

val string = "a"
val result = with(string) {
    // this = "a"
    // it = not available
    3 // Block return value
    // result = 3
}

val string = "a"
val result = string.apply {
    // this = "a"
    // it = not available
    4 // Block return value unused
    // result = "a"
}

Kotlin Basic Learning - series 6

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