Synchronize IME insets with iOS keyboard (#875)

Proper support of the keyboard animation

---------

Co-authored-by: dima.avdeev <dima.avdeev@jetbrains.com>

compose/ui/ui/src/uikitMain/kotlin/androidx/compose/ui/window/ComposeWindow.uikit.kt

@@ -55,19 +55,24 @@ import org.jetbrains.skia.Canvas
 import org.jetbrains.skiko.OS
 import org.jetbrains.skiko.OSVersion
 import org.jetbrains.skiko.SkikoKeyboardEvent
-import platform.CoreGraphics.CGPoint
 import org.jetbrains.skiko.available
 import platform.CoreGraphics.CGAffineTransformIdentity
 import platform.CoreGraphics.CGAffineTransformInvert
+import platform.CoreGraphics.CGFloat
+import platform.CoreGraphics.CGPoint
 import platform.CoreGraphics.CGPointMake
 import platform.CoreGraphics.CGRectMake
 import platform.CoreGraphics.CGSize
 import platform.CoreGraphics.CGSizeEqualToSize
 import platform.Foundation.*
+import platform.QuartzCore.CADisplayLink
+import platform.QuartzCore.CATransaction
+import platform.QuartzCore.kCATransactionDisableActions
 import platform.UIKit.*
 import platform.darwin.NSObject
 import platform.darwin.dispatch_async
 import platform.darwin.dispatch_get_main_queue
+import platform.darwin.sel_registerName
 
 private val uiContentSizeCategoryToFontScaleMap = mapOf(
     UIContentSizeCategoryExtraSmall to 0.8f,
@@ -156,6 +161,14 @@ internal actual class ComposeWindow : UIViewController {
     private var safeArea by mutableStateOf(PlatformInsets())
     private var layoutMargins by mutableStateOf(PlatformInsets())
 
+    //invisible view to track system keyboard animation
+    private val keyboardAnimationView: UIView by lazy {
+        UIView(CGRectMake(0.0, 0.0, 0.0, 0.0)).apply {
+            hidden = true
+        }
+    }
+    private var keyboardAnimationListener: CADisplayLink? = null
+
     /*
      * Initial value is arbitrarily chosen to avoid propagating invalid value logic
      * It's never the case in real usage scenario to reflect that in type system
@@ -219,22 +232,12 @@ internal actual class ComposeWindow : UIViewController {
         @Suppress("unused")
         @ObjCAction
         fun keyboardWillShow(arg: NSNotification) {
-            val keyboardInfo = arg.userInfo!!["UIKeyboardFrameEndUserInfoKey"] as NSValue
-            val keyboardHeight = keyboardInfo.CGRectValue().useContents { size.height }
-            val screenHeight = UIScreen.mainScreen.bounds.useContents { size.height }
-
-            val composeViewBottomY = UIScreen.mainScreen.coordinateSpace.convertPoint(
-                point = CGPointMake(0.0, view.frame.useContents { size.height }),
-                fromCoordinateSpace = view.coordinateSpace
-            ).useContents { y }
-            val bottomIndent = screenHeight - composeViewBottomY
-
-            if (bottomIndent < keyboardHeight) {
-                keyboardOverlapHeight = (keyboardHeight - bottomIndent).toFloat()
-            }
+            animateKeyboard(arg, true)
 
             val scene = attachedComposeContext?.scene ?: return
-
+            val userInfo = arg.userInfo ?: return
+            val keyboardInfo = userInfo[UIKeyboardFrameEndUserInfoKey] as NSValue
+            val keyboardHeight = keyboardInfo.CGRectValue().useContents { size.height }
             if (configuration.onFocusBehavior == OnFocusBehavior.FocusableAboveKeyboard) {
                 val focusedRect = scene.mainOwner?.focusOwner?.getFocusRect()?.toDpRect(density)
 
@@ -249,12 +252,92 @@ internal actual class ComposeWindow : UIViewController {
         @Suppress("unused")
         @ObjCAction
         fun keyboardWillHide(arg: NSNotification) {
-            keyboardOverlapHeight = 0f
+            animateKeyboard(arg, false)
+
             if (configuration.onFocusBehavior == OnFocusBehavior.FocusableAboveKeyboard) {
                 updateViewBounds(offsetY = 0.0)
             }
         }
 
+        private fun animateKeyboard(arg: NSNotification, isShow: Boolean) {
+            val userInfo = arg.userInfo!!
+
+            //return actual keyboard height during animation
+            fun getCurrentKeyboardHeight(): CGFloat {
+                val layer = keyboardAnimationView.layer.presentationLayer() ?: return 0.0
+                return layer.frame.useContents { origin.y }
+            }
+
+            //attach to root view if needed
+            if (keyboardAnimationView.superview == null) {
+                this@ComposeWindow.view.addSubview(keyboardAnimationView)
+            }
+
+            //cancel previous animation
+            keyboardAnimationView.layer.removeAllAnimations()
+            keyboardAnimationListener?.invalidate()
+
+            //synchronize actual keyboard height with keyboardAnimationView without animation
+            val current = getCurrentKeyboardHeight()
+            CATransaction.begin()
+            CATransaction.setValue(true, kCATransactionDisableActions)
+            keyboardAnimationView.setFrame(CGRectMake(0.0, current, 0.0, 0.0))
+            CATransaction.commit()
+
+            //animation listener
+            keyboardAnimationListener = CADisplayLink.displayLinkWithTarget(
+                target = object : NSObject() {
+                    val bottomIndent: CGFloat
+
+                    init {
+                        val screenHeight = UIScreen.mainScreen.bounds.useContents { size.height }
+                        val composeViewBottomY = UIScreen.mainScreen.coordinateSpace.convertPoint(
+                            point = CGPointMake(0.0, view.frame.useContents { size.height }),
+                            fromCoordinateSpace = view.coordinateSpace
+                        ).useContents { y }
+                        bottomIndent = screenHeight - composeViewBottomY
+                    }
+
+                    @Suppress("unused")
+                    @ObjCAction
+                    fun animationDidUpdate() {
+                        val currentHeight = getCurrentKeyboardHeight()
+                        if (bottomIndent < currentHeight) {
+                            keyboardOverlapHeight = (currentHeight - bottomIndent).toFloat()
+                        }
+                    }
+                },
+                selector = sel_registerName("animationDidUpdate")
+            ).apply {
+                addToRunLoop(NSRunLoop.mainRunLoop(), NSDefaultRunLoopMode)
+            }
+
+            //start system animation with duration
+            val duration = userInfo[UIKeyboardAnimationDurationUserInfoKey] as? Double ?: 0.0
+            val toValue: CGFloat = if (isShow) {
+                val keyboardInfo = userInfo[UIKeyboardFrameEndUserInfoKey] as NSValue
+                keyboardInfo.CGRectValue().useContents { size.height }
+            } else {
+                0.0
+            }
+            UIView.animateWithDuration(
+                duration = duration,
+                animations = {
+                    //set final destination for animation
+                    keyboardAnimationView.setFrame(CGRectMake(0.0, toValue, 0.0, 0.0))
+                },
+                completion = { isFinished ->
+                    if (isFinished) {
+                        keyboardAnimationListener?.invalidate()
+                        keyboardAnimationListener = null
+                        keyboardAnimationView.removeFromSuperview()
+                    } else {
+                        //animation was canceled by other animation
+                    }
+                }
+            )
+        }
+
         private fun calcFocusedLiftingY(focusedRect: DpRect, keyboardHeight: Double): Double {
             val viewHeight = attachedComposeContext?.view?.frame?.useContents {
                 size.height