Merge pull request #310 from hotwired/webview-element-scrolling

Prevent pull-to-refresh from triggering while scrolling in a nested scrollable element on the page

Author: jayohms

turbo/src/main/assets/js/turbo_bridge.js

@@ -179,6 +179,37 @@
     }
   }
 
+  // Touch detection, allowing vertically scrollable elements
+  // to scroll properly without triggering pull-to-refresh.
+
+  const elementTouchStart = (event) => {
+    if (!event.target) return
+
+    var element = event.target
+
+    while (element) {
+      const canScroll = element.scrollHeight > element.clientHeight
+      const overflowY = window.getComputedStyle(element).overflowY
+
+      if (canScroll && (overflowY === "scroll" || overflowY === "auto")) {
+        TurboSession.elementTouchStarted(true)
+        break
+      }
+
+      element = element.parentElement
+    }
+
+    if (!element) {
+      TurboSession.elementTouchStarted(false)
+    }
+  }
+
+  const elementTouchEnd = () => {
+    TurboSession.elementTouchEnded()
+  }
+
+  // Setup and register adapter
+
   window.turboNative = new TurboNative()
 
   const setup = function() {
@@ -187,6 +218,9 @@
 
     document.removeEventListener("turbo:load", setup)
     document.removeEventListener("turbolinks:load", setup)
+
+    document.addEventListener("touchstart", elementTouchStart)
+    document.addEventListener("touchend", elementTouchEnd)
   }
 
   const setupOnLoad = () => {

turbo/src/main/kotlin/dev/hotwire/turbo/session/TurboSession.kt

@@ -482,6 +482,28 @@ class TurboSession internal constructor(
         callback { it.onReceivedError(-1) }
     }
 
+    /**
+     * Called when a touched element event has started.
+     *
+     * Warning: This method is public so it can be used as a Javascript Interface.
+     * You should never call this directly as it could lead to unintended behavior.
+     */
+    @JavascriptInterface
+    fun elementTouchStarted(scrollable: Boolean) {
+        webView.elementTouchIsScrollable = scrollable
+    }
+
+    /**
+     * Called when a touched element event has ended.
+     *
+     * Warning: This method is public so it can be used as a Javascript Interface.
+     * You should never call this directly as it could lead to unintended behavior.
+     */
+    @JavascriptInterface
+    fun elementTouchEnded() {
+        webView.elementTouchIsScrollable = false
+    }
+
     // Private
 
     private fun visitLocation(visit: TurboVisit) {

turbo/src/main/kotlin/dev/hotwire/turbo/views/TurboSwipeRefreshLayout.kt

@@ -2,7 +2,6 @@ package dev.hotwire.turbo.views
 
 import android.content.Context
 import android.util.AttributeSet
-import android.webkit.WebView
 import androidx.core.view.children
 import androidx.swiperefreshlayout.widget.SwipeRefreshLayout
 
@@ -14,8 +13,13 @@ internal class TurboSwipeRefreshLayout @JvmOverloads constructor(context: Contex
     }
 
     override fun canChildScrollUp(): Boolean {
-        val webView = children.firstOrNull() as? WebView
-        return webView?.scrollY ?: 0 > 0
+        val webView = children.firstOrNull() as? TurboWebView
+
+        return if (webView != null) {
+            webView.scrollY > 0 || webView.elementTouchIsScrollable
+        } else {
+            false
+        }
     }
 
     /**

turbo/src/main/kotlin/dev/hotwire/turbo/views/TurboWebView.kt

@@ -6,13 +6,12 @@ import android.util.AttributeSet
 import android.webkit.WebView
 import android.widget.FrameLayout
 import android.widget.FrameLayout.LayoutParams.MATCH_PARENT
-import android.widget.FrameLayout.LayoutParams.WRAP_CONTENT
 import androidx.webkit.WebViewCompat
+import com.google.gson.GsonBuilder
 import dev.hotwire.turbo.util.contentFromAsset
 import dev.hotwire.turbo.util.runOnUiThread
 import dev.hotwire.turbo.util.toJson
 import dev.hotwire.turbo.visit.TurboVisitOptions
-import com.google.gson.GsonBuilder
 
 /**
  * A Turbo-specific WebView that configures required settings and exposes some helpful info.
@@ -72,6 +71,8 @@ open class TurboWebView @JvmOverloads constructor(context: Context, attrs: Attri
         }
     }
 
+    internal var elementTouchIsScrollable = false
+
     private fun WebView.runJavascript(javascript: String, onComplete: (String?) -> Unit = {}) {
         context.runOnUiThread {
             evaluateJavascript(javascript) {