port TemplateBinding to ed3266266e751b5ab1f75f8e0509d0d5f0ef35d8

pkg/template_binding/lib/src/node_binding.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.
+
+library template_binding.src.node_binding;
+
+import 'dart:async' show StreamSubscription;
+import 'dart:html' show Node;
+import 'package:observe/observe.dart' show PathObserver, CompoundPathObserver;
+
+/** Test only method. Not re-exported. */
+getObserverForTest(NodeBinding binding) => binding._observer;
+
+/**
+ * A data binding on a [Node].
+ * See [NodeBindExtension.bindings] and [NodeBindExtension.bind].
+ */
+abstract class NodeBinding {
+  Node _node;
+  var _model;
+
+  // TODO(jmesserly): need common interface for PathObserver,
+  // CompoundPathObserver.
+  var _observer;
+  StreamSubscription _pathSub;
+
+  /** The property of [node] which will be data bound. */
+  final String property;
+
+  /** The property of [node] which will be data bound. */
+  final String path;
+
+  /** The node that has [property] which will be data bound. */
+  Node get node => _node;
+
+  /** The bound data model. */
+  get model => _model;
+
+  /** True if this binding has been [closed]. */
+  bool get closed => _node == null;
+
+  /** The value at the [path] on [model]. */
+  get value => _observer.value;
+
+  set value(newValue) {
+    _observer.value = newValue;
+  }
+
+  NodeBinding(this._node, this.property, this._model, [String path])
+      : path = path != null ? path : '' {
+
+    // Fast path if we're observing "value"
+    if ((model is PathObserver || model is CompoundPathObserver) &&
+        path == 'value') {
+
+      _observer = model;
+    } else {
+      // Create the path observer
+      _observer = new PathObserver(model, this.path);
+    }
+
+    _pathSub = _observer.changes.listen((r) => valueChanged(value));
+    valueChanged(value);
+  }
+
+  /** Called when [value] changes to update the [node]. */
+  // TODO(jmesserly): the impl in template_binding uses reflection to set the
+  // property, but that isn't used except for specific known fields like
+  // "textContent", so I'm overridding this in the subclasses instead.
+  void valueChanged(newValue);
+
+  /** Called to sanitize the value before it is assigned into the property. */
+  sanitizeBoundValue(value) => value == null ? '' : '$value';
+
+  /**
+   * Called by [NodeBindExtension.unbind] to close this binding and unobserve
+   * the [path].
+   *
+   * This can be overridden in subclasses, but they must call `super.close()`
+   * to free associated resources. They must also check [closed] and return
+   * immediately if already closed.
+   */
+  void close() {
+    if (closed) return;
+
+    if (_pathSub != null) _pathSub.cancel();
+    _pathSub = null;
+    _observer = null;
+    _node = null;
+    _model = null;
+  }
+}