Add helpers for creating UI components.

mojo/ui/content_viewer_app.h

+// 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.
+
+#ifndef MOJO_UI_CONTENT_VIEWER_APP_H_
+#define MOJO_UI_CONTENT_VIEWER_APP_H_
+
+#include "mojo/common/strong_binding_set.h"
+#include "mojo/services/content_handler/interfaces/content_handler.mojom.h"
+#include "mojo/ui/view_provider_app.h"
+
+namespace mojo {
+namespace ui {
+
+// A simple ContentHandler application implementation for rendering
+// content as Views.  Subclasses must provide a function to create
+// the view provider application on demand.
+//
+// TODO(jeffbrown): Support creating the view provider application in a
+// separate thread if desired (often not the case).  This is one reason
+// we are not using the ContentHandlerFactory here.
+class ContentViewerApp : public mojo::ApplicationDelegate,
+                         public mojo::InterfaceFactory<mojo::ContentHandler> {
+ public:
+  ContentViewerApp();
+  ~ContentViewerApp() override;
+
+  mojo::ApplicationImpl* app_impl() { return app_impl_; }
+
+  // |ApplicationDelegate|:
+  void Initialize(mojo::ApplicationImpl* app) override;
+  bool ConfigureIncomingConnection(
+      mojo::ApplicationConnection* connection) override;
+
+  // Called to create the view provider application to view the content.
+  //
+  // This method may be called multiple times to load different content
+  // into separate view providers.  The view provider implementation should
+  // cache the loaded content in case it is asked to create multiple instances
+  // of the view since the response can only be consumed once.
+  //
+  // The |content_handler_url| is the connection URL of the content handler
+  // request.
+  // The |response| carries the data retrieved by the content handler.
+  //
+  // Returns the view provider application delegate to view the content,
+  // or nullptr if the content could not be loaded.
+  virtual ViewProviderApp* LoadContent(const std::string& content_handler_url,
+                                       mojo::URLResponsePtr response) = 0;
+
+ private:
+  class DelegatingContentHandler;
+
+  // |InterfaceFactory<ContentHandler>|:
+  void Create(mojo::ApplicationConnection* connection,
+              mojo::InterfaceRequest<mojo::ContentHandler> request) override;
+
+  void StartViewer(
+      const std::string& content_handler_url,
+      mojo::InterfaceRequest<mojo::Application> application_request,
+      mojo::URLResponsePtr response);
+
+  mojo::ApplicationImpl* app_impl_ = nullptr;
+  mojo::StrongBindingSet<mojo::ContentHandler> bindings_;
+
+  MOJO_DISALLOW_COPY_AND_ASSIGN(ContentViewerApp);
+};
+
+}  // namespace ui
+}  // namespace mojo
+
+#endif  // MOJO_UI_CONTENT_VIEWER_APP_H_