fix: non-scrollable ScrollView when blankSpace is big should make it scrollable

android/src/main/java/com/reactnativekeyboardcontroller/views/ClippingScrollViewDecoratorView.kt

@@ -1,12 +1,14 @@
 package com.reactnativekeyboardcontroller.views
 
 import android.annotation.SuppressLint
+import android.view.MotionEvent
 import android.view.View
 import android.view.ViewGroup
 import android.widget.ScrollView
 import com.facebook.react.uimanager.ThemedReactContext
 import com.facebook.react.views.view.ReactViewGroup
 import com.reactnativekeyboardcontroller.extensions.px
+import kotlin.math.max
 
 @SuppressLint("ViewConstructor")
 class ClippingScrollViewDecoratorView(
@@ -15,13 +17,42 @@ class ClippingScrollViewDecoratorView(
   private var insetBottom = 0.0
   private var insetTop = 0.0
   private var appliedTopInsetPx = 0
+  private var paddingScrollWorkaroundActive = false
 
   override fun onAttachedToWindow() {
     super.onAttachedToWindow()
 
     decorateScrollView()
   }
 
+  override fun dispatchTouchEvent(event: MotionEvent): Boolean {
+    val scrollView = findScrollView(this)
+
+    if (scrollView == null) {
+      return super.dispatchTouchEvent(event)
+    }
+
+    if (event.actionMasked == MotionEvent.ACTION_DOWN) {
+      paddingScrollWorkaroundActive = shouldUsePaddingScrollWorkaround(scrollView, event)
+    }
+
+    val handled =
+      if (paddingScrollWorkaroundActive) {
+        dispatchWithExpandedContentRange(scrollView, event)
+      } else {
+        super.dispatchTouchEvent(event)
+      }
+
+    if (
+      event.actionMasked == MotionEvent.ACTION_UP ||
+      event.actionMasked == MotionEvent.ACTION_CANCEL
+    ) {
+      paddingScrollWorkaroundActive = false
+    }
+
+    return handled
+  }
+
   fun setContentInsetBottom(value: Double) {
     insetBottom = value
     decorateScrollView()
@@ -68,6 +99,65 @@ class ClippingScrollViewDecoratorView(
     appliedTopInsetPx = newTopInsetPx
   }
 
+  private fun shouldUsePaddingScrollWorkaround(
+    scrollView: ScrollView,
+    event: MotionEvent,
+  ): Boolean {
+    val contentView = scrollView.getChildAt(0) ?: return false
+    val viewportHeight =
+      scrollView.height - scrollView.paddingTop - scrollView.paddingBottom
+    val paddingCreatesScrollRange = contentView.height > viewportHeight
+
+    return scrollView.scrollY == 0 &&
+      paddingCreatesScrollRange &&
+      !scrollView.canScrollVertically(1) &&
+      isTouchInScrollContent(scrollView, event)
+  }
+
+  private fun dispatchWithExpandedContentRange(
+    scrollView: ScrollView,
+    event: MotionEvent,
+  ): Boolean {
+    val contentView = scrollView.getChildAt(0) ?: return super.dispatchTouchEvent(event)
+    val originalBottom = contentView.bottom
+    val expandedBottom =
+      max(originalBottom, scrollView.height + scrollView.scrollY + MIN_SCROLL_RANGE_PX)
+
+    if (expandedBottom == originalBottom) {
+      return super.dispatchTouchEvent(event)
+    }
+
+    return try {
+      contentView.bottom = expandedBottom
+      super.dispatchTouchEvent(event)
+    } finally {
+      contentView.bottom = originalBottom
+    }
+  }
+
+  private fun isTouchInScrollContent(
+    scrollView: ScrollView,
+    event: MotionEvent,
+  ): Boolean {
+    val contentView = scrollView.getChildAt(0) ?: return false
+    val thisLocation = IntArray(COORDINATES_SIZE)
+    val scrollViewLocation = IntArray(COORDINATES_SIZE)
+
+    getLocationOnScreen(thisLocation)
+    scrollView.getLocationOnScreen(scrollViewLocation)
+
+    val x = event.x + thisLocation[0] - scrollViewLocation[0]
+    val y = event.y + thisLocation[1] - scrollViewLocation[1]
+    val scrollY = scrollView.scrollY
+
+    return !(
+      y < contentView.top - scrollY ||
+        y >= contentView.bottom - scrollY ||
+        x < contentView.left ||
+        x >= contentView.right
+    )
+  }
+
   private fun findScrollView(view: View?): ScrollView? {
     var result: ScrollView? = null
 
@@ -83,4 +173,9 @@ class ClippingScrollViewDecoratorView(
 
     return result
   }
+
+  companion object {
+    private const val COORDINATES_SIZE = 2
+    private const val MIN_SCROLL_RANGE_PX = 2
+  }
 }