Foldable widgets: added keyboard navigation, removed (broken) animation.

app/test/frontend/static_files_test.dart

@@ -200,7 +200,7 @@ void main() {
     test('script.dart.js and parts size check', () {
       final file = cache.getFile('/static/js/script.dart.js');
       expect(file, isNotNull);
-      expect((file!.bytes.length / 1024).round(), closeTo(313, 1));
+      expect((file!.bytes.length / 1024).round(), closeTo(317, 1));
 
       final parts = cache.paths
           .where((path) =>

pkg/web_app/lib/src/foldable.dart

@@ -2,6 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+import 'dart:async';
 import 'dart:html';
 import 'dart:math' show min, max;
 
@@ -22,41 +23,26 @@ void _setEventForFoldable() {
     final scrollContainer = _parentWithClass(h, 'scroll-container');
     if (content == null) continue;
 
-    Future<void> update(bool isActive) async {
-      // Closing is simple: no measurements, no scrolling.
+    Future<void> toggle() async {
+      final isActive = foldable.classes.toggle('-active');
       if (!isActive) {
-        content.style.maxHeight = '0px';
         return;
       }
 
-      /// The following coordinate and dimension measurements trigger a reflow,
-      /// but it is acceptable, as it is local to this event processing and the
-      /// impact is low.
-      if (content.style.display != 'block') {
-        content.style.display = 'block';
-      }
-      // Needs to be empty to measure real dimension.
-      content.style.maxHeight = '';
-
-      final contentHeight = content.offsetHeight;
-      final boundingRect = content.getBoundingClientRect();
-      final scrollContainerHeight = scrollContainer?.clientHeight;
-      final buttonHeight = h.offsetHeight;
-
-      // Reset content state as hidden.
-      content.style.maxHeight = '0px';
-
-      // Wait one animation frame before trigger the full height content.
-      await window.animationFrame;
-      content.style.maxHeight = '${contentHeight}px';
-
       num scrollDiff = 0;
       if (scrollContainer != null) {
+        // Wait one animation frame before measurements.
+        await window.animationFrame;
+
+        final boundingRect = content.getBoundingClientRect();
+        final scrollContainerHeight = scrollContainer.clientHeight;
+        final buttonHeight = h.offsetHeight;
+
         /// Calculate the required amount of scrolling in order to have the
         /// entire content in the view, aligning it at the bottom of the visible
         /// scroll view.
         final outsideViewDiff =
-            boundingRect.top + boundingRect.height - scrollContainerHeight!;
+            boundingRect.top + boundingRect.height - scrollContainerHeight;
 
         /// Limit the maximum scrolling to the screen height minus the button
         /// component's height, in order to make sure it will be still visible
@@ -65,30 +51,31 @@ void _setEventForFoldable() {
 
         /// Scroll the smaller amount of the two.
         scrollDiff = max(0, min(screenLimit, outsideViewDiff));
-      }
 
-      /// Do not scroll if the difference is small, otherwise scroll in small
-      /// steps synchronized to the animation frames.
-      if (scrollDiff > 8) {
-        final originalScrollTop = scrollContainer!.scrollTop;
-        final maxSteps = 20;
-        for (var i = 1; i <= maxSteps; i++) {
-          if (i > 1) await window.animationFrame;
-          final nextPos = originalScrollTop + (scrollDiff * i / maxSteps);
-          scrollContainer.scrollTo(0, nextPos);
+        /// Do not scroll if the difference is small, otherwise scroll in small
+        /// steps synchronized to the animation frames.
+        if (scrollDiff > 8) {
+          final originalScrollTop = scrollContainer.scrollTop;
+          final maxSteps = 20;
+          for (var i = 1; i <= maxSteps; i++) {
+            if (i > 1) await window.animationFrame;
+            final nextPos = originalScrollTop + (scrollDiff * i / maxSteps);
+            scrollContainer.scrollTo(0, nextPos);
+          }
         }
       }
-
-      // Wait one animation frame before enabling the content to resize on its own.
-      await window.animationFrame;
-      content.style.maxHeight = 'none';
     }
 
+    h.querySelector('.foldable-icon')!.attributes['tabindex'] = '0';
+
     // listen on trigger events
     h.onClick.listen((e) async {
-      // Toggle state.
-      final isActive = foldable.classes.toggle('-active');
-      await update(isActive);
+      e.preventDefault();
+      await toggle();
+    });
+    h.onKeyDown.where((e) => e.key == 'Enter').listen((e) async {
+      e.preventDefault();
+      await toggle();
     });
   }
 }

pkg/web_css/lib/src/_base.scss

@@ -380,8 +380,6 @@ pre {
 .foldable {
   .foldable-content {
     display: none;
-    overflow: hidden;
-    transition: max-height 0.6s ease;
   }
 
   &.-active {