hoang06kx1 · October 4, 2023 15:20 · Oct 12, 2020
diff --git a/NestedScrollableHost.kt b/NestedScrollableHost.kt
@@ -0,0 +1,118 @@
+/*
+ * Copyright 2019 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package androidx.viewpager2.integration.testapp
+
+import android.content.Context
+import android.util.AttributeSet
+import android.view.MotionEvent
+import android.view.View
+import android.view.ViewConfiguration
+import android.widget.FrameLayout
+import androidx.viewpager2.widget.ViewPager2
+import androidx.viewpager2.widget.ViewPager2.ORIENTATION_HORIZONTAL
+import kotlin.math.absoluteValue
+import kotlin.math.sign
+
+/**
+ * Layout to wrap a scrollable component inside a ViewPager2. Provided as a solution to the problem
+ * where pages of ViewPager2 have nested scrollable elements that scroll in the same direction as
+ * ViewPager2. The scrollable element needs to be the immediate and only child of this host layout.
+ *
+ * This solution has limitations when using multiple levels of nested scrollable elements
+ * (e.g. a horizontal RecyclerView in a vertical RecyclerView in a horizontal ViewPager2).
+ */
+class NestedScrollableHost : FrameLayout {
+    constructor(context: Context) : super(context)
+    constructor(context: Context, attrs: AttributeSet?) : super(context, attrs)
+
+    private var touchSlop = 0
+    private var initialX = 0f
+    private var initialY = 0f
+    private val parentViewPager: ViewPager2?
+        get() {
+            var v: View? = parent as? View
+            while (v != null && v !is ViewPager2) {
+                v = v.parent as? View
+            }
+            return v as? ViewPager2
+        }
+
+    private val child: View? get() = if (childCount > 0) getChildAt(0) else null
+
+    init {
+        touchSlop = ViewConfiguration.get(context).scaledTouchSlop
+    }
+
+    private fun canChildScroll(orientation: Int, delta: Float): Boolean {
+        val direction = -delta.sign.toInt()
+        return when (orientation) {
+            0 -> child?.canScrollHorizontally(direction) ?: false
+            1 -> child?.canScrollVertically(direction) ?: false
+            else -> throw IllegalArgumentException()
+        }
+    }
+
+    override fun onInterceptTouchEvent(e: MotionEvent): Boolean {
+        return handleInterceptTouchEvent(e) || super.onInterceptTouchEvent(e)
+    }
+
+    /**
+     * @return The child does not need to scroll.
+     */
+    private fun handleInterceptTouchEvent(e: MotionEvent): Boolean {
+        val orientation = parentViewPager?.orientation ?: return false
+
+        // Early return if child can't scroll in same direction as parent
+        if (!canChildScroll(orientation, -1f) && !canChildScroll(orientation, 1f)) {
+            return false
+        }
+
+        if (e.action == MotionEvent.ACTION_DOWN) {
+            initialX = e.x
+            initialY = e.y
+            parent.requestDisallowInterceptTouchEvent(true)
+        } else if (e.action == MotionEvent.ACTION_MOVE) {
+            val dx = e.x - initialX
+            val dy = e.y - initialY
+            val isVpHorizontal = orientation == ORIENTATION_HORIZONTAL
+
+            if (dx.absoluteValue > touchSlop || dy.absoluteValue > touchSlop) {
+                if (isVpHorizontal == (dy.absoluteValue > dx.absoluteValue)) {
+                    // Gesture is perpendicular, allow all parents to intercept
+                    parent.requestDisallowInterceptTouchEvent(false)
+
+                    // If you are the following case:
+                    // ViewPager2(V) -> NestedScrollView(V) -> RecyclerView(H)
+                    // return false instead so that the innermost RV(H) can scroll normally.
+                    // It is not tested for other use case.
+                    return true
+                } else {
+                    // Gesture is parallel, query child if movement in that direction is possible
+                    if (canChildScroll(orientation, if (isVpHorizontal) dx else dy)) {
+                        // Child can scroll, disallow all parents to intercept
+                        parent.requestDisallowInterceptTouchEvent(true)
+                    } else {
+                        // Child cannot scroll, allow all parents to intercept
+                        parent.requestDisallowInterceptTouchEvent(false)
+                        return true
+                    }
+                }
+            }
+        }
+        return false
+    }
+}
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