mozart: Introduce new view manager interfaces.

mojo/services/ui/views/interfaces/view_trees.mojom

+// 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.
+
+[DartPackage="mojo_services"]
+module mojo.ui;
+
+import "mojo/services/ui/views/interfaces/layouts.mojom";
+import "mojo/services/ui/views/interfaces/views.mojom";
+
+// A view tree is a top-level container for a hierarchy of views.
+//
+// A view tree must registered with the view manager before it can be shown.
+interface ViewTree {
+  // Called when the tree needs to update its layout.
+  //
+  // This method may be called for one or more of the following reasons:
+  //
+  //   1. The root was just set.
+  //   2. The root produced different layout information during its last
+  //      layout pass causing a recursive layout to occur.
+  //
+  // Layout requests are coalesced for efficiency.  Certain intermediate
+  // updates may be dropped if the view tree is unable to keep up with them
+  // in a timely manner.  Do nothing updates are always dropped.
+  //
+  // The implementation should invoke the callback once the event has
+  // been handled and the view tree is ready to be shown in its new aspect.
+  OnLayout() => ();
+
+  // Called when the root view has become unavailable.
+  //
+  // The root may become unavailable for many reasons such being unregistered
+  // by its application, abnormal termination of its application, or
+  // being reparented into a different view tree.
+  //
+  // The implementation should invoke the callback once the event has
+  // been handled.
+  OnRootUnavailable(uint32 root_key) => ();
+};
+
+// The view tree host provides an interface for a view tree to configure itself
+// and interact with its views.
+//
+// Each view tree obtains its own view tree host when registered with the
+// ViewManager.  To unregister the view tree, close its view tree
+// and/or view tree host message pipes.
+interface ViewTreeHost {
+  // Requests that the view tree's OnLayout() method be called to compute a
+  // new layout due to a change in the view tree's layout information.
+  RequestLayout();
+
+  // Sets the root of the view tree and assigns it the provided |root_key|
+  // to distinguish it from any other roots this view tree has had.
+  //
+  // It is a good idea to provide a distinct |root_key| each time a new root
+  // is set so that callbacks related to the root can be clearly distinguished
+  // across these changes.
+  //
+  // If |root_view_token| refers to a view which is already unavailable
+  // then the call proceeds as if it succeeded but an OnChildUnavailable()
+  // message will be sent.
+  //
+  // If |root_view_token| refers to a view which already has a parent or is
+  // the root of a view tree then an OnChildUnavailable() or OnRootUnavailable()
+  // message will be sent to its old parent or root and the the view will be
+  // used as the root of the new view tree as usual.  This special case also
+  // applies when the specified view is already the root of this view tree, in
+  // which case the behavior is similar to the view having been transferred to
+  // some other view tree and then back again.
+  SetRoot(uint32 root_key, mojo.ui.ViewToken root_view_token);
+
+  // Removes the root of the view tree.
+  //
+  // Does nothing if the view tree currently does not have a root.
+  ResetRoot();
+
+  // Sets the layout parameters of the root of the view tree and retrieves
+  // its layout information.
+  //
+  // The returned |info| is null if this layout request was canceled either
+  // because it has been superceded by a subsequently issued layout request
+  // or because the root has become unavailable.
+  //
+  // It is an error to call this function if the view tree does not currently
+  // have a root; the connection will be closed.
+  //
+  // It is an error to specify malformed |root_layout_params| such
+  // as invalid size constraints; the connection will be closed.
+  LayoutRoot(mojo.ui.ViewLayoutParams root_layout_params) =>
+      (mojo.ui.ViewLayoutInfo? info);
+};