[package:mdv] Support binding to HTMLSelectElement.selectedIndex

pkg/mdv/lib/src/select_element.dart

+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// 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.
+
+part of mdv;
+
+/** Extensions to the [SelectElement] API. */
+class _SelectElementExtension extends _ElementExtension {
+  _SelectElementExtension(SelectElement node) : super(node);
+
+  SelectElement get node => super.node;
+
+  _SelectedIndexBinding _valueBinding;
+
+  void bind(String name, model, String path) {
+    if (name.toLowerCase() == 'selectedindex') {
+      unbind('selectedindex');
+      node.attributes.remove('selectedindex');
+      _valueBinding = new _SelectedIndexBinding(node, model, path);
+      return;
+    }
+    super.bind(name, model, path);
+  }
+
+  void unbind(String name) {
+    if (name.toLowerCase() == 'selectedindex' && _valueBinding != null) {
+      _valueBinding.unbind();
+      _valueBinding = null;
+      return;
+    }
+    super.unbind(name);
+  }
+
+  void unbindAll() {
+    unbind('selectedindex');
+    super.unbindAll();
+  }
+}
+
+
+class _SelectedIndexBinding extends _InputBinding {
+  _SelectedIndexBinding(element, model, path) : super(element, model, path);
+
+  SelectElement get element => super.element;
+
+  void valueChanged(value) {
+    var newValue = _toInt(value);
+    if (newValue <= element.length) {
+      element.selectedIndex = newValue;
+      return;
+    }
+
+    // The binding may wish to bind to an <option> which has not yet been
+    // produced by a child <template>. Delay a maximum of twice -- once for
+    // iterating <optgroup> and once for <option>.
+    var maxRetries = 2;
+    delaySetSelectedIndex() {
+      if (newValue > element.length && --maxRetries >= 0) {
+        runAsync(delaySetSelectedIndex);
+      } else {
+        element.selectedIndex = newValue;
+      }
+    }
+
+    // TODO(jmesserly): we aren't matching MDV here. They schedule "model=" to
+    // happen async and then delay using the same scheduler. By using "runAsync"
+    // we're going to happen quite a bit later.
+    // We need to port the "ensureScheduled" function:
+    // https://github.com/Polymer/mdv/commit/9a51ad7ed74a292bf71662cea28acbd151ff65c8
+    runAsync(delaySetSelectedIndex);
+  }
+
+  void updateBinding(e) {
+    binding.value = element.selectedIndex;
+  }
+
+  // TODO(jmesserly,sigmund): I wonder how many bindings typically convert from
+  // one type to another (e.g. value-as-number) and whether it is useful to
+  // have something like a int/num binding converter (either as a base class or
+  // a wrapper).
+  static int _toInt(value) {
+    if (value is String) return int.parse(value, onError: (_) => null);
+    return value is int ? value : null;
+  }
+}