Dart: Wait to handle events on a Stub until it makes sense to do it.

mojo/dart/packages/mojo_services/lib/mojo/ui/view_manager.mojom.dart

 // Copyright 2014 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.
 
 library view_manager_mojom;
 import 'dart:async';
 import 'package:mojo/bindings.dart' as bindings;
 import 'package:mojo/core.dart' as core;
 import 'package:mojo/mojo/bindings/types/service_describer.mojom.dart' as service_describer;
 import 'package:mojo_services/mojo/ui/view_token.mojom.dart' as view_token_mojom;
@@ skipping 347 matching lines @@
     impl.requireVersion(requiredVersion);
   }
 
   String toString() {
     return "ViewManagerProxy($impl)";
   }
 }
 
 
 class ViewManagerStub extends bindings.Stub {
-  ViewManager _impl = null;
+  ViewManager _impl;
 
   ViewManagerStub.fromEndpoint(
-      core.MojoMessagePipeEndpoint endpoint, [this._impl])
-      : super.fromEndpoint(endpoint);
+      core.MojoMessagePipeEndpoint endpoint, [ViewManager impl])
+      : super.fromEndpoint(endpoint, autoBegin: impl != null) {
+    _impl = impl;
+  }
 
-  ViewManagerStub.fromHandle(core.MojoHandle handle, [this._impl])
-      : super.fromHandle(handle);
+  ViewManagerStub.fromHandle(
+      core.MojoHandle handle, [ViewManager impl])
+      : super.fromHandle(handle, autoBegin: impl != null) {
+    _impl = impl;
+  }
 
   ViewManagerStub.unbound() : super.unbound();
 
   static ViewManagerStub newFromEndpoint(
       core.MojoMessagePipeEndpoint endpoint) {
     assert(endpoint.setDescription("For ViewManagerStub"));
     return new ViewManagerStub.fromEndpoint(endpoint);
   }
 
 
 
   dynamic handleMessage(bindings.ServiceMessage message) {
     if (bindings.ControlMessageHandler.isControlMessage(message)) {
       return bindings.ControlMessageHandler.handleMessage(this,
                                                           0,
                                                           message);
     }
-    assert(_impl != null);
+    if (_impl == null) {
+      throw new core.MojoApiError("$this has no implementation set");
+    }
     switch (message.header.type) {
       case _viewManagerMethodCreateViewName:
         var params = _ViewManagerCreateViewParams.deserialize(
             message.payload);
         _impl.createView(params.view, params.viewOwner, params.viewListener, params.label);
         break;
       case _viewManagerMethodCreateViewTreeName:
         var params = _ViewManagerCreateViewTreeParams.deserialize(
             message.payload);
         _impl.createViewTree(params.viewTree, params.viewTreeListener, params.label);
         break;
       default:
         throw new bindings.MojoCodecError("Unexpected message name");
         break;
     }
     return null;
   }
 
   ViewManager get impl => _impl;
   set impl(ViewManager d) {
-    assert(_impl == null);
+    if (d == null) {
+      throw new core.MojoApiError("$this: Cannot set a null implementation");
+    }
+    if (isBound && (_impl == null)) {
+      beginHandlingEvents();
+    }
     _impl = d;
   }
 
+  @override
+  void bind(core.MojoMessagePipeEndpoint endpoint) {
+    super.bind(endpoint);
+    if (!isOpen && (_impl != null)) {
+      beginHandlingEvents();
+    }
+  }
+
   String toString() {
     var superString = super.toString();
     return "ViewManagerStub($superString)";
   }
 
   int get version => 0;
 
   static service_describer.ServiceDescription _cachedServiceDescription;
   static service_describer.ServiceDescription get serviceDescription {
     if (_cachedServiceDescription == null) {
       _cachedServiceDescription = new _ViewManagerServiceDescription();
     }
     return _cachedServiceDescription;
   }
 }