Android KTX · Kotin知識點難點歸納總結

[Android KTX](https://developer.android.com/kotlin/ktx) Android KTX是一組Kotlin擴展，是Android [Jetpack](https://developer.android.com/jetpack)系列的一部分。它優化了Jetpack和Android平臺API以供Kotlin使用。Android KTX的目的是通過利用Kotlin語言功能（如擴展函數/屬性，lambdas，命名參數和參數默認值），使Kotlin的Android開發更簡潔，愉快和慣用。Android KTX不會為現有的Android API添加任何新功能。要了解有關Android KTX的更多信息，請參閱我們的[DevBytes視頻](https://www.youtube.com/watch?v=r_19VZ0xRO8&feature=youtu.be)。 #### 入門要開始使用Android KTX，請將以下內容添加到項目的build.gradle文件中： ~~~ repositories { google() } ~~~ Android KTX被組織成模塊。每個模塊包含一個或多個包。使用模塊時，請在應用程序build.gradle文件中包含每個Android KTX工件的依賴項。請記住將版本附加到工件。例如，如果使用core-ktx模塊，則完全形成的依賴關系將如下所示： ~~~ dependencies { implementation 'androidx.core:core-ktx:1.0.0-alpha1' } ~~~ ### 模塊 Android KTX由以下Maven工件組成。對于API參考文檔，請單擊特定包名稱并查看擴展功能摘要。 * androidx.core：核心KTX 1.0.0-α1 查看下面的[所有核心包](https://developer.android.com/kotlin/ktx#core-packages)。 * androidx.fragment：片段KTX 1.0.0-α1 [androidx.fragment.app](https://developer.android.com/reference/kotlin/androidx/fragment/app/package-summary#extension-functions-summary) * androidx.palette：調色板KTX 1.0.0-α1 [androidx.palette.graphics](https://developer.android.com/reference/kotlin/androidx/palette/graphics/package-summary#extension-functions-summary) * androidx.sqlite：sqlite的，KTX 1.0.0-α1 [androidx.sqlite.db](https://developer.android.com/reference/kotlin/androidx/sqlite/db/package-summary#extension-functions-summary) * androidx.collection：收集，KTX 1.0.0-α1 [androidx.collection](https://developer.android.com/reference/kotlin/androidx/collection/package-summary#extension-functions-summary) * androidx.lifecycle：生命周期 - 視圖模型，KTX 2.0.0-α1 [androidx.lifecycle](https://developer.android.com/reference/kotlin/androidx/lifecycle/package-summary#extension-functions-summary) * androidx.lifecycle：生命周期reactivestreams，KTX 2.0.0-α1 [androidx.lifecycle](https://developer.android.com/reference/kotlin/androidx/lifecycle/package-summary#extension-functions-summary) * android.arch.navigation：導航，共KTX 1.0.0-alpha01 [androidx.navigation](https://developer.android.com/reference/kotlin/androidx/navigation/package-summary#extension-functions-summary) * android.arch.navigation：導航片段的KTX 1.0.0-alpha01 [androidx.navigation.fragment](https://developer.android.com/reference/kotlin/androidx/navigation/fragment/package-summary#extension-functions-summary) * android.arch.navigation：導航運行，KTX 1.0.0-alpha01 [androidx.navigation](https://developer.android.com/reference/kotlin/androidx/navigation/package-summary#extension-functions-summary) * android.arch.navigation：導航測試，KTX 1.0.0-alpha01 [androidx.navigation.testing](https://developer.android.com/reference/kotlin/androidx/navigation/testing/package-summary#extension-functions-summary) * android.arch.navigation：導航-UI-KTX 1.0.0-alpha01 [androidx.navigation.ui](https://developer.android.com/reference/kotlin/androidx/navigation/ui/package-summary#extension-functions-summary) * android.arch.work:work-runtime-ktx 1.0.0-alpha01 [androidx.work.ktx](https://developer.android.com/reference/kotlin/androidx/work/ktx/package-summary#extension-functions-summary) #### 核心模塊包括以下軟件包： * [androidx.core.animation](https://developer.android.com/reference/kotlin/androidx/core/animation/package-summary#extension-functions-summary) * [androidx.core.content](https://developer.android.com/reference/kotlin/androidx/core/content/package-summary#extension-functions-summary) * [androidx.core.graphics](https://developer.android.com/reference/kotlin/androidx/core/graphics/package-summary#extension-functions-summary) * [androidx.core.graphics.drawable](https://developer.android.com/reference/kotlin/androidx/core/graphics/drawable/package-summary#extension-functions-summary) * [androidx.core.net](https://developer.android.com/reference/kotlin/androidx/core/net/package-summary#extension-functions-summary) * [androidx.core.os](https://developer.android.com/reference/kotlin/androidx/core/os/package-summary#extension-functions-summary) * [androidx.core.preference](https://developer.android.com/reference/kotlin/androidx/core/preference/package-summary#extension-functions-summary) * [androidx.core.text](https://developer.android.com/reference/kotlin/androidx/core/text/package-summary#extension-functions-summary) * [androidx.core.transition](https://developer.android.com/reference/kotlin/androidx/core/transition/package-summary#extension-functions-summary) * [androidx.core.util](https://developer.android.com/reference/kotlin/androidx/core/util/package-summary#extension-functions-summary) * [androidx.core.view](https://developer.android.com/reference/kotlin/androidx/core/view/package-summary#extension-functions-summary) * [androidx.core.widget](https://developer.android.com/reference/kotlin/androidx/core/widget/package-summary#extension-functions-summary) ### 例子 Android KTX是[Android Jetpack](https://developer.android.com/jetpack/)基礎組件。在[Sunflower](https://github.com/googlesamples/android-sunflower)演示應用程序中查看它的使用情況。以下示例演示了一些Android KTX擴展功能。它們按模塊（工件）名稱分組。有關擴展功能的完整列表，請參閱完整的包參考文檔。 #### androidx.core：核心KTX ① **KOTLIN** ~~~ sharedPreferences.edit() .putBoolean("key", value) .apply() ~~~ **KOTLIN + ANDROID KTX** ~~~ sharedPreferences.edit { putBoolean("key", value) } ~~~ ② **KOTLIN** ~~~ view.viewTreeObserver.addOnPreDrawListener( object : ViewTreeObserver.OnPreDrawListener { override fun onPreDraw(): Boolean { viewTreeObserver.removeOnPreDrawListener(this) actionToBeTriggered() return true } } ) ~~~ **KOTLIN + ANDROID KTX** ~~~ view.doOnPreDraw { actionToBeTriggered() } ~~~ #### androidx.sqlite:sqlite-ktx **KOTLIN** ~~~ db.beginTransaction() try { // insert data db.setTransactionSuccessful() } finally { db.endTransaction() } ~~~ **KOTLIN + ANDROID KTX** ~~~ db.transaction { // insert data } ~~~ #### androidx.fragment:fragment-ktx **KOTLIN** ~~~ supportFragmentManager .beginTransaction() .replace(R.id.my_fragment_container, myFragment, FRAGMENT_TAG) .commitAllowingStateLoss() ~~~ **KOTLIN + ANDROID KTX** ~~~ supportFragmentManager.transaction(allowStateLoss = true) { replace(R.id.my_fragment_container, myFragment, FRAGMENT_TAG) } ~~~ #### 反饋 Android KTX目前在Alpha。我們將繼續在Jetpack中添加新的Kotlin擴展，我們歡迎您的反饋。如果您想報告問題或建議功能，請在Android KTX 問題跟蹤器上提交新問題。