bug: Statistics Zoom Issue-16135

AnkiDroid/src/main/java/com/ichi2/anki/pages/Statistics.kt

@@ -49,6 +49,8 @@ class Statistics :
 
     override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
         super.onViewCreated(view, savedInstanceState)
+        webView.isNestedScrollingEnabled = true
+
         requireActivity().setTransparentStatusBar()
         spinner = view.findViewById(R.id.deck_selector)
         view.findViewById<AppBarLayout>(R.id.app_bar)

AnkiDroid/src/main/java/com/ichi2/anki/workarounds/NestedScrollingWebView.kt

@@ -0,0 +1,183 @@
+/*
+ *  Copyright (c) 2024 deysak <[email protected]>
+ *
+ *  This program is free software; you can redistribute it and/or modify it under
+ *  the terms of the GNU General Public License as published by the Free Software
+ *  Foundation; either version 3 of the License, or (at your option) any later
+ *  version.
+ *
+ *  This program is distributed in the hope that it will be useful, but WITHOUT ANY
+ *  WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
+ *  PARTICULAR PURPOSE. See the GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License along with
+ *  this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *
+ *  This file incorporates code under the following license:
+ *
+ *   Copyright (C) 2015 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.
+ *
+ *  https://cs.android.com/androidx/platform/frameworks/support/+/5c27b70c8541f02542fca57734ac8d3be6db45a5:core/core/src/main/java/androidx/core/widget/NestedScrollView.java
+ */
+
+package com.ichi2.anki.workarounds
+
+import android.content.Context
+import android.util.AttributeSet
+import android.view.MotionEvent
+import android.webkit.WebView
+import androidx.core.view.NestedScrollingChild
+import androidx.core.view.NestedScrollingChildHelper
+import androidx.core.view.ViewCompat
+import androidx.core.view.ViewCompat.ScrollAxis
+import androidx.core.widget.NestedScrollView
+
+/**
+ * NestedScrollingWebView is-a [WebView] that implements [NestedScrollingChild].
+ *
+ * It is useful for purposes where [WebView] is required to be:
+ *  1. Scrollable
+ *  2. Zoomable
+ *  3. Supporting nested scrolling
+ *
+ * **Example:** Hiding the toolbar upon scroll
+ * ([Issue-14991](https://github.com/ankidroid/Anki-Android/issues/14991)).
+ *
+ * **Need:**
+ * There is no default way to reliably support all the 3 aforementioned behaviors as:
+ *  * Using [NestedScrollView] interferes with the zoom
+ *  ([Issue-16135](https://github.com/ankidroid/Anki-Android/issues/16135)).
+ * * Intercepting the scale motion events from [NestedScrollView]
+ * and passing it to [WebView] is unreliable.
+ * * Hiding the toolbar by detecting scroll is unreliable.
+ * * Workarounds for ensuring reliable zoom behavior interferes with scrolling.
+ * * Methods allowing consistent scroll and zoom behavior are not reliable for hiding toolbar.
+ *
+ * **Usage:**
+ * 1. [WebView.setNestedScrollingEnabled] must be set to `true`.
+ * 2. XML: `<com.ichi2.anki.workarounds.NestedScrollingWebView ... />`
+ */
+class NestedScrollingWebView @JvmOverloads constructor(
+    context: Context,
+    attrs: AttributeSet? = null,
+    defStyleAttr: Int = android.R.attr.webViewStyle
+) : WebView(context, attrs, defStyleAttr), NestedScrollingChild {
+    private val yAxis: Int = 1
+
+    private val deltaX: Int = 0
+
+    /*
+     * https://developer.android.com/reference/androidx/core/view/NestedScrollingChild
+     * Classes implementing this interface should create a final instance of
+     * a NestedScrollingChildHelper as a field and delegate any View methods to
+     * the NestedScrollingChildHelper methods of the same signature.
+     */
+    private val childHelper: NestedScrollingChildHelper = NestedScrollingChildHelper(this)
+
+    private val scrollOffset: IntArray = IntArray(2)
+
+    private val scrollConsumed: IntArray = IntArray(2)
+
+    private var lastMotionY: Int = 0
+
+    private var nestedYOffset: Int = 0
+
+    override fun onTouchEvent(motionEvent: MotionEvent): Boolean {
+        val actionMasked: Int = motionEvent.actionMasked
+        if (actionMasked == MotionEvent.ACTION_DOWN) {
+            nestedYOffset = 0
+        }
+
+        val velocityTrackerMotionEvent: MotionEvent = MotionEvent.obtain(motionEvent)
+        handleOffset(velocityTrackerMotionEvent, nestedYOffset)
+
+        val motionEventY: Int = motionEvent.y.toInt()
+        when (actionMasked) {
+            MotionEvent.ACTION_DOWN -> {
+                lastMotionY = motionEventY
+                startNestedScroll(ViewCompat.SCROLL_AXIS_VERTICAL)
+            }
+
+            MotionEvent.ACTION_MOVE -> {
+                val scrollDistanceY: Int = lastMotionY - motionEventY
+                if (dispatchNestedPreScroll(
+                        deltaX,
+                        scrollDistanceY,
+                        scrollConsumed,
+                        scrollOffset
+                    )
+                ) {
+                    handleOffset(velocityTrackerMotionEvent, scrollOffset[yAxis])
+                    nestedYOffset += scrollOffset[yAxis]
+                }
+                lastMotionY = motionEventY - scrollOffset[yAxis]
+            }
+
+            MotionEvent.ACTION_UP, MotionEvent.ACTION_CANCEL,
+            MotionEvent.ACTION_POINTER_DOWN, MotionEvent.ACTION_POINTER_UP -> {
+                stopNestedScroll()
+            }
+        }
+
+        velocityTrackerMotionEvent.recycle()
+        return super.onTouchEvent(velocityTrackerMotionEvent)
+    }
+
+    private fun handleOffset(velocityTrackerMotionEvent: MotionEvent, deltaY: Int) {
+        velocityTrackerMotionEvent.offsetLocation(deltaX.toFloat(), deltaY.toFloat())
+    }
+
+    override fun setNestedScrollingEnabled(enabled: Boolean) =
+        childHelper.setNestedScrollingEnabled(enabled)
+
+    override fun isNestedScrollingEnabled() = childHelper.isNestedScrollingEnabled
+
+    override fun startNestedScroll(@ScrollAxis axes: Int) = childHelper.startNestedScroll(axes)
+
+    override fun stopNestedScroll() = childHelper.stopNestedScroll()
+
+    override fun hasNestedScrollingParent() = childHelper.hasNestedScrollingParent()
+
+    override fun dispatchNestedScroll(
+        dxConsumed: Int,
+        dyConsumed: Int,
+        dxUnconsumed: Int,
+        dyUnconsumed: Int,
+        offsetInWindow: IntArray?
+    ) = childHelper.dispatchNestedScroll(
+        dxConsumed,
+        dyConsumed,
+        dxUnconsumed,
+        dyUnconsumed,
+        offsetInWindow
+    )
+
+    override fun dispatchNestedPreScroll(
+        dx: Int,
+        dy: Int,
+        consumed: IntArray?,
+        offsetInWindow: IntArray?
+    ) = childHelper.dispatchNestedPreScroll(dx, dy, consumed, offsetInWindow)
+
+    override fun dispatchNestedFling(
+        velocityX: Float,
+        velocityY: Float,
+        consumed: Boolean
+    ) = childHelper.dispatchNestedFling(velocityX, velocityY, consumed)
+
+    override fun dispatchNestedPreFling(velocityX: Float, velocityY: Float) =
+        childHelper.dispatchNestedPreFling(velocityX, velocityY)
+}

AnkiDroid/src/main/res/layout/statistics.xml

@@ -41,15 +41,11 @@
         </com.google.android.material.appbar.MaterialToolbar>
     </com.google.android.material.appbar.AppBarLayout>
 
-    <androidx.core.widget.NestedScrollView
+    <com.ichi2.anki.workarounds.NestedScrollingWebView
+        android:id="@+id/webview"
         android:layout_width="match_parent"
         android:layout_height="match_parent"
-        app:layout_behavior="@string/appbar_scrolling_view_behavior">
-        <WebView
-            android:id="@+id/webview"
-            android:layout_width="match_parent"
-            android:layout_height="match_parent"
-            android:visibility="invisible"/>
-    </androidx.core.widget.NestedScrollView>
+        app:layout_behavior="@string/appbar_scrolling_view_behavior"
+        android:visibility="invisible"/>
 
 </androidx.coordinatorlayout.widget.CoordinatorLayout>