Move VariableHeightScrollable to sdk/lib/widgets

sky/sdk/lib/widgets/variable_height_scrollable.dart

+// Copyright 2015 The Chromium Authors. 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:collection';
+
+import '../animation/scroll_behavior.dart';
+import 'basic.dart';
+import 'block_viewport.dart';
+import 'scrollable.dart';
+import 'widget.dart';
+
+class VariableHeightScrollable extends Scrollable {
+  VariableHeightScrollable({
+    String key,
+    this.builder,
+    this.token
+  }) : super(key: key);
+
+  IndexedBuilder builder;
+  Object token;
+
+  void syncFields(VariableHeightScrollable source) {
+    builder = source.builder;
+    token = source.token;
+    super.syncFields(source);
+  }
+
+  ScrollBehavior createScrollBehavior() => new OverscrollBehavior();
+  OverscrollBehavior get scrollBehavior => super.scrollBehavior;
+
+  void _handleSizeChanged(Size newSize) {
+    setState(() {
+      scrollBehavior.containerHeight = newSize.height;
+    });
+  }
+
+  void _handleLayoutChanged(
+      int firstVisibleWidgetIndex, 
+      int visibleWidgetCount,
+      UnmodifiableListView<double> widgetOffsets,
+      bool lastWidgetReached) {
+    assert(widgetOffsets.length > 0);
+
+    scrollBehavior.contentsHeight = lastWidgetReached ? widgetOffsets.last : null;
+    
+    // We don't know the height of all items yet. Grow the ScrollBehavior's

[Hixie, 2015/07/10 22:51:38]

delete comment-out code

[hansmuller, 2015/07/10 23:42:06]

Done.

+    // contentsHeight a little, to accomodate scrolling further.
+    /*
+    if (!lastWidgetReached)
+      scrollBehavior.contentsHeight += scrollBehavior.containerHeight;
+    */
+
+    if (lastWidgetReached && scrollOffset > scrollBehavior.maxScrollOffset)
+      settleScrollOffset();
+  }
+
+  Widget buildContent() {
+    return new SizeObserver(
+      callback: _handleSizeChanged,
+      child: new BlockViewport(
+        builder: builder,
+        onLayoutChanged: _handleLayoutChanged,
+        startOffset: scrollOffset,
+        token: token
+      )
+    );
+  }
+}