style: improve Kotlin code

android/src/main/java/com/swmansion/rnscreens/CustomSearchView.kt

@@ -22,7 +22,9 @@ class CustomSearchView(context: Context, fragment: Fragment) : SearchView(contex
                 isIconified = true
             }
         }
+
     private val backPressOverrider = FragmentBackPressOverrider(fragment, mOnBackPressedCallback)
+
     var overrideBackAction: Boolean
         set(value) {
             backPressOverrider.overrideBackAction = value

android/src/main/java/com/swmansion/rnscreens/LifecycleHelper.kt

@@ -43,8 +43,7 @@ class LifecycleHelper {
     }
 
     fun <T> unregister(view: T) where T : View, T : LifecycleObserver? {
-        val lifecycle = mViewToLifecycleMap[view]
-        lifecycle?.removeObserver(view)
+        mViewToLifecycleMap[view]?.removeObserver(view)
     }
 
     companion object {

android/src/main/java/com/swmansion/rnscreens/RNSUtil.kt

@@ -0,0 +1,5 @@
+package com.swmansion.rnscreens
+
+public inline fun <T> Iterable<T>.forEachSatisfying(predicate: (T) -> Boolean, action: (T) -> Unit) {
+    for (element in this) if (predicate(element)) action(element)
+}

android/src/main/java/com/swmansion/rnscreens/RNScreensPackage.kt

@@ -15,7 +15,7 @@ class RNScreensPackage : ReactPackage {
             // This should no longer be needed if RN's autolink mechanism has Fabric support
             SoLoader.loadLibrary("rnscreens_modules")
         }
-        return emptyList<NativeModule>()
+        return emptyList()
     }
 
     override fun createViewManagers(reactContext: ReactApplicationContext) =

android/src/main/java/com/swmansion/rnscreens/Screen.kt

@@ -84,12 +84,7 @@ class Screen constructor(context: ReactContext?) : FabricEnabledViewGroup(contex
     }
 
     val headerConfig: ScreenStackHeaderConfig?
-        get() {
-            val child = getChildAt(0)
-            return if (child is ScreenStackHeaderConfig) {
-                child
-            } else null
-        }
+        get() = getChildAt(0).takeIf { it is ScreenStackHeaderConfig } as ScreenStackHeaderConfig?
 
     /**
      * While transitioning this property allows to optimize rendering behavior on Android and provide

android/src/main/java/com/swmansion/rnscreens/ScreenContainer.kt

@@ -35,6 +35,7 @@ open class ScreenContainer<T : ScreenFragment>(context: Context?) : ViewGroup(co
         }
     }
     private var mParentScreenFragment: ScreenFragment? = null
+
     override fun onLayout(changed: Boolean, l: Int, t: Int, r: Int, b: Int) {
         var i = 0
         val size = childCount
@@ -116,19 +117,10 @@ open class ScreenContainer<T : ScreenFragment>(context: Context?) : ViewGroup(co
     val screenCount: Int
         get() = mScreenFragments.size
 
-    fun getScreenAt(index: Int): Screen {
-        return mScreenFragments[index].screen
-    }
+    fun getScreenAt(index: Int): Screen = mScreenFragments[index].screen
 
     open val topScreen: Screen?
-        get() {
-            for (screenFragment in mScreenFragments) {
-                if (getActivityState(screenFragment) === ActivityState.ON_TOP) {
-                    return screenFragment.screen
-                }
-            }
-            return null
-        }
+        get() = mScreenFragments.firstOrNull { getActivityState(it) === ActivityState.ON_TOP }?.screen
 
     private fun setFragmentManager(fm: FragmentManager) {
         mFragmentManager = fm
@@ -200,10 +192,9 @@ open class ScreenContainer<T : ScreenFragment>(context: Context?) : ViewGroup(co
     }
 
     protected fun createTransaction(): FragmentTransaction {
-        val fragmentManager = requireNotNull(mFragmentManager, { "mFragmentManager is null when creating transaction" })
-        val transaction = fragmentManager.beginTransaction()
-        transaction.setReorderingAllowed(true)
-        return transaction
+        return requireNotNull(mFragmentManager) { "mFragmentManager is null when creating transaction" }
+            .beginTransaction()
+            .setReorderingAllowed(true)
     }
 
     private fun attachScreen(transaction: FragmentTransaction, screenFragment: ScreenFragment) {
@@ -214,13 +205,11 @@ open class ScreenContainer<T : ScreenFragment>(context: Context?) : ViewGroup(co
         transaction.remove(screenFragment)
     }
 
-    private fun getActivityState(screenFragment: ScreenFragment): ActivityState? {
-        return screenFragment.screen.activityState
-    }
+    private fun getActivityState(screenFragment: ScreenFragment): ActivityState? =
+        screenFragment.screen.activityState
 
-    open fun hasScreen(screenFragment: ScreenFragment?): Boolean {
-        return mScreenFragments.contains(screenFragment)
-    }
+    open fun hasScreen(screenFragment: ScreenFragment?): Boolean =
+        mScreenFragments.contains(screenFragment)
 
     override fun onAttachedToWindow() {
         super.onAttachedToWindow()
@@ -233,9 +222,7 @@ open class ScreenContainer<T : ScreenFragment>(context: Context?) : ViewGroup(co
         val transaction = fragmentManager.beginTransaction()
         var hasFragments = false
         for (fragment in fragmentManager.fragments) {
-            if (fragment is ScreenFragment &&
-                fragment.screen.container === this
-            ) {
+            if (fragment is ScreenFragment && fragment.screen.container === this) {
                 transaction.remove(fragment)
                 hasFragments = true
             }
@@ -284,11 +271,9 @@ open class ScreenContainer<T : ScreenFragment>(context: Context?) : ViewGroup(co
 
     override fun onMeasure(widthMeasureSpec: Int, heightMeasureSpec: Int) {
         super.onMeasure(widthMeasureSpec, heightMeasureSpec)
-        var i = 0
         val size = childCount
-        while (i < size) {
+        for (i in 0 until size) {
             getChildAt(i).measure(widthMeasureSpec, heightMeasureSpec)
-            i++
         }
     }
 
@@ -332,7 +317,11 @@ open class ScreenContainer<T : ScreenFragment>(context: Context?) : ViewGroup(co
     open fun onUpdate() {
         createTransaction().let {
             // detach screens that are no longer active
-            val orphaned: MutableSet<Fragment> = HashSet(requireNotNull(mFragmentManager, { "mFragmentManager is null when performing update in ScreenContainer" }).fragments)
+            val orphaned: MutableSet<Fragment> = HashSet(
+                requireNotNull(mFragmentManager) {
+                    "mFragmentManager is null when performing update in ScreenContainer"
+                }.fragments
+            )
             for (screenFragment in mScreenFragments) {
                 if (getActivityState(screenFragment) === ActivityState.INACTIVE &&
                     screenFragment.isAdded

android/src/main/java/com/swmansion/rnscreens/ScreenContainerViewManager.kt

@@ -9,13 +9,9 @@ import com.facebook.react.uimanager.ViewGroupManager
 
 @ReactModule(name = ScreenContainerViewManager.REACT_CLASS)
 class ScreenContainerViewManager : ViewGroupManager<ScreenContainer<*>>() {
-    override fun getName(): String {
-        return REACT_CLASS
-    }
+    override fun getName(): String = REACT_CLASS
 
-    override fun createViewInstance(reactContext: ThemedReactContext): ScreenContainer<ScreenFragment> {
-        return ScreenContainer(reactContext)
-    }
+    override fun createViewInstance(reactContext: ThemedReactContext): ScreenContainer<ScreenFragment> = ScreenContainer(reactContext)
 
     override fun addView(parent: ScreenContainer<*>, child: View, index: Int) {
         require(child is Screen) { "Attempt attach child that is not of type RNScreens" }
@@ -30,21 +26,13 @@ class ScreenContainerViewManager : ViewGroupManager<ScreenContainer<*>>() {
         parent.removeAllScreens()
     }
 
-    override fun getChildCount(parent: ScreenContainer<*>): Int {
-        return parent.screenCount
-    }
+    override fun getChildCount(parent: ScreenContainer<*>): Int = parent.screenCount
 
-    override fun getChildAt(parent: ScreenContainer<*>, index: Int): View {
-        return parent.getScreenAt(index)
-    }
+    override fun getChildAt(parent: ScreenContainer<*>, index: Int): View = parent.getScreenAt(index)
 
-    override fun createShadowNodeInstance(context: ReactApplicationContext): LayoutShadowNode {
-        return ScreensShadowNode(context)
-    }
+    override fun createShadowNodeInstance(context: ReactApplicationContext): LayoutShadowNode = ScreensShadowNode(context)
 
-    override fun needsCustomLayoutForChildren(): Boolean {
-        return true
-    }
+    override fun needsCustomLayoutForChildren(): Boolean = true
 
     companion object {
         const val REACT_CLASS = "RNSScreenContainer"

android/src/main/java/com/swmansion/rnscreens/ScreenFragment.kt

@@ -74,13 +74,12 @@ open class ScreenFragment : Fragment {
         container: ViewGroup?,
         savedInstanceState: Bundle?
     ): View? {
-        val wrapper = context?.let { ScreensFrameLayout(it) }
-
-        val params = FrameLayout.LayoutParams(
+        screen.layoutParams = FrameLayout.LayoutParams(
             ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT
         )
-        screen.layoutParams = params
-        wrapper?.addView(recycleView(screen))
+        val wrapper = context?.let { ScreensFrameLayout(it) }?.apply {
+            addView(recycleView(screen))
+        }
         return wrapper
     }
 
@@ -153,13 +152,11 @@ open class ScreenFragment : Fragment {
     val childScreenContainers: List<ScreenContainer<*>>
         get() = mChildScreenContainers
 
-    private fun canDispatchEvent(event: ScreenLifecycleEvent): Boolean {
-        return when (event) {
-            ScreenLifecycleEvent.WillAppear -> canDispatchWillAppear
-            ScreenLifecycleEvent.Appear -> canDispatchAppear
-            ScreenLifecycleEvent.WillDisappear -> !canDispatchWillAppear
-            ScreenLifecycleEvent.Disappear -> !canDispatchAppear
-        }
+    private fun canDispatchEvent(event: ScreenLifecycleEvent): Boolean = when (event) {
+        ScreenLifecycleEvent.WillAppear -> canDispatchWillAppear
+        ScreenLifecycleEvent.Appear -> canDispatchAppear
+        ScreenLifecycleEvent.WillDisappear -> !canDispatchWillAppear
+        ScreenLifecycleEvent.Disappear -> !canDispatchAppear
     }
 
     private fun setLastEventDispatched(event: ScreenLifecycleEvent) {
@@ -173,25 +170,21 @@ open class ScreenFragment : Fragment {
 
     private fun dispatchOnWillAppear() {
         dispatchEvent(ScreenLifecycleEvent.WillAppear, this)
-
         dispatchTransitionProgress(0.0f, false)
     }
 
     private fun dispatchOnAppear() {
         dispatchEvent(ScreenLifecycleEvent.Appear, this)
-
         dispatchTransitionProgress(1.0f, false)
     }
 
     private fun dispatchOnWillDisappear() {
         dispatchEvent(ScreenLifecycleEvent.WillDisappear, this)
-
         dispatchTransitionProgress(0.0f, true)
     }
 
     private fun dispatchOnDisappear() {
         dispatchEvent(ScreenLifecycleEvent.Disappear, this)
-
         dispatchTransitionProgress(1.0f, true)
     }
 
@@ -215,20 +208,16 @@ open class ScreenFragment : Fragment {
     }
 
     private fun dispatchEventInChildContainers(event: ScreenLifecycleEvent) {
-        for (sc in mChildScreenContainers) {
-            if (sc.screenCount > 0) {
-                sc.topScreen?.let {
-                    sc.topScreen?.fragment?.let { fragment -> dispatchEvent(event, fragment) }
-                }
-            }
+        mChildScreenContainers.filter { it.screenCount > 0 }.forEach {
+            it.topScreen?.fragment?.let { fragment -> dispatchEvent(event, fragment) }
         }
     }
 
     fun dispatchHeaderBackButtonClickedEvent() {
         val screenContext = screen.context as ReactContext
-        val eventDispatcher: EventDispatcher? =
-            UIManagerHelper.getEventDispatcherForReactTag(screenContext, screen.id)
-        eventDispatcher?.dispatchEvent(HeaderBackButtonClickedEvent(screen.id))
+        UIManagerHelper
+            .getEventDispatcherForReactTag(screenContext, screen.id)
+            ?.dispatchEvent(HeaderBackButtonClickedEvent(screen.id))
     }
 
     fun dispatchTransitionProgress(alpha: Float, closing: Boolean) {
@@ -244,13 +233,13 @@ open class ScreenFragment : Fragment {
                 val container: ScreenContainer<*>? = screen.container
                 val goingForward = if (container is ScreenStack) container.goingForward else false
                 val screenContext = screen.context as ReactContext
-                val eventDispatcher: EventDispatcher? =
-                    UIManagerHelper.getEventDispatcherForReactTag(screenContext, screen.id)
-                eventDispatcher?.dispatchEvent(
-                    ScreenTransitionProgressEvent(
-                        screen.id, mProgress, closing, goingForward, coalescingKey
+                UIManagerHelper
+                    .getEventDispatcherForReactTag(screenContext, screen.id)
+                    ?.dispatchEvent(
+                        ScreenTransitionProgressEvent(
+                            screen.id, mProgress, closing, goingForward, coalescingKey
+                        )
                     )
-                )
             }
         }
     }
@@ -305,9 +294,9 @@ open class ScreenFragment : Fragment {
             // we only send dismissed even when the screen has been removed from its container
             val screenContext = screen.context
             if (screenContext is ReactContext) {
-                val eventDispatcher: EventDispatcher? =
-                    UIManagerHelper.getEventDispatcherForReactTag(screenContext, screen.id)
-                eventDispatcher?.dispatchEvent(ScreenDismissedEvent(screen.id))
+                UIManagerHelper
+                    .getEventDispatcherForReactTag(screenContext, screen.id)
+                    ?.dispatchEvent(ScreenDismissedEvent(screen.id))
             }
         }
         mChildScreenContainers.clear()