Fix onBegin and onTouchesDown events ordering on Android

android/src/main/java/com/swmansion/gesturehandler/core/GestureHandler.kt

@@ -57,6 +57,7 @@ open class GestureHandler<ConcreteGestureHandlerT : GestureHandler<ConcreteGestu
   var lastAbsolutePositionY = 0f
     private set
 
+  private var isInitialized = false
   private var manualActivation = false
 
   private var lastEventOffsetX = 0f
@@ -68,6 +69,10 @@ open class GestureHandler<ConcreteGestureHandlerT : GestureHandler<ConcreteGestu
   private var onTouchEventListener: OnTouchEventListener? = null
   private var interactionController: GestureHandlerInteractionController? = null
 
+  // a field to store a motion event that caused the touch event to be dispatched, in case the state
+  // change is triggered in the callback, this event will be used to initialize the gesture
+  private var eventTriggeringStateChangeInTouchEventHandler: MotionEvent? = null
+
   @Suppress("UNCHECKED_CAST")
   protected fun self(): ConcreteGestureHandlerT = this as ConcreteGestureHandlerT
 
@@ -88,8 +93,8 @@ open class GestureHandler<ConcreteGestureHandlerT : GestureHandler<ConcreteGestu
     onTouchEventListener?.onHandlerUpdate(self(), event)
   }
 
-  open fun dispatchTouchEvent() {
-    if (changedTouchesPayload != null) {
+  open fun tryDispatchingTouchEvent() {
+    if (needsPointerData && changedTouchesPayload != null) {
       onTouchEventListener?.onTouchEvent(self())
     }
   }
@@ -380,7 +385,7 @@ open class GestureHandler<ConcreteGestureHandlerT : GestureHandler<ConcreteGestu
     }
   }
 
-  private fun dispatchTouchDownEvent(event: MotionEvent) {
+  private fun handleTouchDownEvent(event: MotionEvent) {
     changedTouchesPayload = null
     touchEventType = RNGestureHandlerTouchEvent.EVENT_TOUCH_DOWN
     val pointerId = event.getPointerId(event.actionIndex)
@@ -398,10 +403,10 @@ open class GestureHandler<ConcreteGestureHandlerT : GestureHandler<ConcreteGestu
     addChangedPointer(trackedPointers[pointerId]!!)
     extractAllPointersData()
 
-    dispatchTouchEvent()
+    tryDispatchingTouchEvent()
   }
 
-  private fun dispatchTouchUpEvent(event: MotionEvent) {
+  private fun handleTouchUpEvent(event: MotionEvent) {
     extractAllPointersData()
     changedTouchesPayload = null
     touchEventType = RNGestureHandlerTouchEvent.EVENT_TOUCH_UP
@@ -420,10 +425,10 @@ open class GestureHandler<ConcreteGestureHandlerT : GestureHandler<ConcreteGestu
     trackedPointers[pointerId] = null
     trackedPointersCount--
 
-    dispatchTouchEvent()
+    tryDispatchingTouchEvent()
   }
 
-  private fun dispatchTouchMoveEvent(event: MotionEvent) {
+  private fun handleTouchMoveEvent(event: MotionEvent) {
     changedTouchesPayload = null
     touchEventType = RNGestureHandlerTouchEvent.EVENT_TOUCH_MOVE
     val offsetX = event.rawX - event.x
@@ -450,20 +455,28 @@ open class GestureHandler<ConcreteGestureHandlerT : GestureHandler<ConcreteGestu
     // only info about one pointer)
     if (pointersAdded > 0) {
       extractAllPointersData()
-      dispatchTouchEvent()
+      tryDispatchingTouchEvent()
     }
   }
 
-  fun updatePointerData(event: MotionEvent) {
-    if (event.actionMasked == MotionEvent.ACTION_DOWN || event.actionMasked == MotionEvent.ACTION_POINTER_DOWN) {
-      dispatchTouchDownEvent(event)
-      dispatchTouchMoveEvent(event)
-    } else if (event.actionMasked == MotionEvent.ACTION_UP || event.actionMasked == MotionEvent.ACTION_POINTER_UP) {
-      dispatchTouchMoveEvent(event)
-      dispatchTouchUpEvent(event)
-    } else if (event.actionMasked == MotionEvent.ACTION_MOVE) {
-      dispatchTouchMoveEvent(event)
+  fun updatePointerData(event: MotionEvent, sourceEvent: MotionEvent) {
+    eventTriggeringStateChangeInTouchEventHandler = sourceEvent
+
+    when (event.actionMasked) {
+      MotionEvent.ACTION_DOWN, MotionEvent.ACTION_POINTER_DOWN -> {
+        handleTouchDownEvent(event)
+        handleTouchMoveEvent(event)
+      }
+      MotionEvent.ACTION_UP, MotionEvent.ACTION_POINTER_UP -> {
+        handleTouchMoveEvent(event)
+        handleTouchUpEvent(event)
+      }
+      MotionEvent.ACTION_MOVE -> {
+        handleTouchMoveEvent(event)
+      }
     }
+
+    eventTriggeringStateChangeInTouchEventHandler = null
   }
 
   private fun extractAllPointersData() {
@@ -490,7 +503,7 @@ open class GestureHandler<ConcreteGestureHandlerT : GestureHandler<ConcreteGestu
     trackedPointersCount = 0
     trackedPointers.fill(null)
 
-    dispatchTouchEvent()
+    tryDispatchingTouchEvent()
   }
 
   private fun addChangedPointer(pointerData: PointerData) {
@@ -667,6 +680,17 @@ open class GestureHandler<ConcreteGestureHandlerT : GestureHandler<ConcreteGestu
     }
   }
 
+  fun initialize(withEvent: MotionEvent? = null) {
+    if (!isInitialized) {
+      val event = withEvent ?: eventTriggeringStateChangeInTouchEventHandler ?: throw IllegalStateException("No event to initialize handler")
+      onInitialize(event)
+    }
+
+    isInitialized = true
+  }
+
+  open fun onInitialize(event: MotionEvent) {}
+
   // responsible for resetting the state of handler upon activation (may be called more than once
   // if the handler is waiting for failure of other one)
   open fun resetProgress() {}
@@ -703,6 +727,7 @@ open class GestureHandler<ConcreteGestureHandlerT : GestureHandler<ConcreteGestu
     trackedPointersCount = 0
     trackedPointers.fill(null)
     touchEventType = RNGestureHandlerTouchEvent.EVENT_UNDETERMINED
+    isInitialized = false
     onReset()
   }
 

android/src/main/java/com/swmansion/gesturehandler/core/GestureHandlerOrchestrator.kt

@@ -259,20 +259,9 @@ class GestureHandlerOrchestrator(
     val action = sourceEvent.actionMasked
     val event = transformEventToViewCoords(handler.view, MotionEvent.obtain(sourceEvent))
 
-    // Touch events are sent before the handler itself has a chance to process them,
-    // mainly because `onTouchesUp` shoul be send befor gesture finishes. This means that
-    // the first `onTouchesDown` event is sent before a gesture begins, activation in
-    // callback for this event causes problems because the handler doesn't have a chance
-    // to initialize itself with starting values of pointer (in pan this causes translation
-    // to be equal to the coordinates of the pointer). The simplest solution is to send
-    // the first `onTouchesDown` event after the handler processes it and changes state
-    // to `BEGAN`.
-    if (handler.needsPointerData && handler.state != 0) {
-      handler.updatePointerData(event)
-    }
+    handler.updatePointerData(event, sourceEvent)
 
     if (!handler.isAwaiting || action != MotionEvent.ACTION_MOVE) {
-      val isFirstEvent = handler.state == 0
       handler.handle(event, sourceEvent)
       if (handler.isActive) {
         // After handler is done waiting for other one to fail its progress should be
@@ -289,10 +278,6 @@ class GestureHandlerOrchestrator(
         handler.dispatchHandlerUpdate(event)
       }
 
-      if (handler.needsPointerData && isFirstEvent) {
-        handler.updatePointerData(event)
-      }
-
       // if event was of type UP or POINTER_UP we request handler to stop tracking now that
       // the event has been dispatched
       if (action == MotionEvent.ACTION_UP || action == MotionEvent.ACTION_POINTER_UP) {

android/src/main/java/com/swmansion/gesturehandler/core/LongPressGestureHandler.kt

@@ -39,11 +39,8 @@ class LongPressGestureHandler(context: Context) : GestureHandler<LongPressGestur
 
   override fun onHandle(event: MotionEvent, sourceEvent: MotionEvent) {
     if (state == STATE_UNDETERMINED) {
-      previousTime = SystemClock.uptimeMillis()
-      startTime = previousTime
+      initialize(sourceEvent)
       begin()
-      startX = sourceEvent.rawX
-      startY = sourceEvent.rawY
       handler = Handler(Looper.getMainLooper())
       if (minDurationMs > 0) {
         handler!!.postDelayed({ activate() }, minDurationMs)
@@ -83,6 +80,13 @@ class LongPressGestureHandler(context: Context) : GestureHandler<LongPressGestur
     }
   }
 
+  override fun onInitialize(event: MotionEvent) {
+    previousTime = SystemClock.uptimeMillis()
+    startTime = previousTime
+    startX = event.rawX
+    startY = event.rawY
+  }
+
   override fun dispatchStateChange(newState: Int, prevState: Int) {
     previousTime = SystemClock.uptimeMillis()
     super.dispatchStateChange(newState, prevState)

android/src/main/java/com/swmansion/gesturehandler/core/PanGestureHandler.kt

@@ -225,12 +225,7 @@ class PanGestureHandler(context: Context?) : GestureHandler<PanGestureHandler>()
       lastY = getLastPointerY(sourceEvent, averageTouches)
     }
     if (state == STATE_UNDETERMINED && sourceEvent.pointerCount >= minPointers) {
-      resetProgress()
-      offsetX = 0f
-      offsetY = 0f
-      velocityX = 0f
-      velocityY = 0f
-      velocityTracker = VelocityTracker.obtain()
+      initialize(sourceEvent)
       addVelocityMovement(velocityTracker, sourceEvent)
       begin()
 
@@ -285,6 +280,15 @@ class PanGestureHandler(context: Context?) : GestureHandler<PanGestureHandler>()
     handler?.removeCallbacksAndMessages(null)
   }
 
+  override fun onInitialize(event: MotionEvent) {
+    resetProgress()
+    offsetX = 0f
+    offsetY = 0f
+    velocityX = 0f
+    velocityY = 0f
+    velocityTracker = VelocityTracker.obtain()
+  }
+
   override fun onReset() {
     handler?.removeCallbacksAndMessages(null)
     velocityTracker?.let {

android/src/main/java/com/swmansion/gesturehandler/core/PinchGestureHandler.kt

@@ -52,16 +52,7 @@ class PinchGestureHandler : GestureHandler<PinchGestureHandler>() {
 
   override fun onHandle(event: MotionEvent, sourceEvent: MotionEvent) {
     if (state == STATE_UNDETERMINED) {
-      val context = view!!.context
-      resetProgress()
-      scaleGestureDetector = ScaleGestureDetector(context, gestureListener)
-      val configuration = ViewConfiguration.get(context)
-      spanSlop = configuration.scaledTouchSlop.toFloat()
-
-      // set the focal point to the position of the first pointer as NaN causes the event not to arrive
-      this.focalPointX = event.x
-      this.focalPointY = event.y
-
+      initialize(sourceEvent)
       begin()
     }
     scaleGestureDetector?.onTouchEvent(sourceEvent)
@@ -96,6 +87,18 @@ class PinchGestureHandler : GestureHandler<PinchGestureHandler>() {
     resetProgress()
   }
 
+  override fun onInitialize(event: MotionEvent) {
+    resetProgress()
+    val context = view!!.context
+    val configuration = ViewConfiguration.get(context)
+    scaleGestureDetector = ScaleGestureDetector(context, gestureListener)
+    spanSlop = configuration.scaledTouchSlop.toFloat()
+
+    // set the focal point to the position of the first pointer as NaN causes the event not to arrive
+    this.focalPointX = event.x
+    this.focalPointY = event.y
+  }
+
   override fun resetProgress() {
     velocity = 0.0
     scale = 1.0

android/src/main/java/com/swmansion/gesturehandler/core/RotationGestureHandler.kt

@@ -43,13 +43,7 @@ class RotationGestureHandler : GestureHandler<RotationGestureHandler>() {
 
   override fun onHandle(event: MotionEvent, sourceEvent: MotionEvent) {
     if (state == STATE_UNDETERMINED) {
-      resetProgress()
-      rotationGestureDetector = RotationGestureDetector(gestureListener)
-
-      // set the anchor to the position of the first pointer as NaN causes the event not to arrive
-      this.anchorX = event.x
-      this.anchorY = event.y
-
+      initialize(sourceEvent)
       begin()
     }
     rotationGestureDetector?.onTouchEvent(sourceEvent)
@@ -75,6 +69,15 @@ class RotationGestureHandler : GestureHandler<RotationGestureHandler>() {
     super.activate(force)
   }
 
+  override fun onInitialize(event: MotionEvent) {
+    resetProgress()
+    rotationGestureDetector = RotationGestureDetector(gestureListener)
+
+    // set the anchor to the position of the first pointer as NaN causes the event not to arrive
+    this.anchorX = event.x
+    this.anchorY = event.y
+  }
+
   override fun onReset() {
     rotationGestureDetector = null
     anchorX = Float.NaN

android/src/main/java/com/swmansion/gesturehandler/core/TapGestureHandler.kt

@@ -108,10 +108,7 @@ class TapGestureHandler : GestureHandler<TapGestureHandler>() {
     val state = state
     val action = sourceEvent.actionMasked
     if (state == STATE_UNDETERMINED) {
-      offsetX = 0f
-      offsetY = 0f
-      startX = getLastPointerX(sourceEvent, true)
-      startY = getLastPointerY(sourceEvent, true)
+      initialize(sourceEvent)
     }
     if (action == MotionEvent.ACTION_POINTER_UP || action == MotionEvent.ACTION_POINTER_DOWN) {
       offsetX += lastX - startX
@@ -148,6 +145,13 @@ class TapGestureHandler : GestureHandler<TapGestureHandler>() {
     end()
   }
 
+  override fun onInitialize(event: MotionEvent) {
+    offsetX = 0f
+    offsetY = 0f
+    startX = getLastPointerX(event, true)
+    startY = getLastPointerY(event, true)
+  }
+
   override fun onCancel() {
     handler?.removeCallbacksAndMessages(null)
   }

android/src/main/java/com/swmansion/gesturehandler/react/RNGestureHandlerModule.kt

@@ -431,9 +431,15 @@ class RNGestureHandlerModule(reactContext: ReactApplicationContext?) :
 
   override fun setGestureHandlerState(handlerTag: Int, newState: Int) {
     registry.getHandler(handlerTag)?.let { handler ->
+      // Try to initialize the handler in case it was not yet initialized
+      handler.initialize()
+      // Try to transition to the BEGIN state (possible only from UNDETERMINED)
+      // to force the correct event flow
+      handler.begin()
+
       when (newState) {
         GestureHandler.STATE_ACTIVE -> handler.activate(force = true)
-        GestureHandler.STATE_BEGAN -> handler.begin()
+        GestureHandler.STATE_BEGAN -> {}
         GestureHandler.STATE_END -> handler.end()
         GestureHandler.STATE_FAILED -> handler.fail()
         GestureHandler.STATE_CANCELLED -> handler.cancel()