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// Copyright 2019 The Fuchsia 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 fuchsia.ui.focus;
using fuchsia.ui.views;
/// A FocusChain tracks the status of the View hierarchy as View focus changes.
/// Description. The `focus_chain` is a vector of ViewRefs in order of
/// dominance in the View hierarchy; each pair of elements represents a
/// parent-child relationship. The root View is always present and occupies
/// slot 0. The newly-focused View receives a fuchsia.ui.input.FocusEvent and
/// occupies the final slot in the vector. If a View gets destroyed, a
/// FocusChain holder that listens will receive a `ZX_EVENTPAIR_PEER_CLOSED`
/// signal on the corresponding ViewRef.
/// Invalidation. A FocusChain is invalid if one if its ViewRefs is invalid.
/// Reception. Only certain components may receive a FocusChain, as it
/// captures global information about the scene graph.
resource table FocusChain {
1: vector<fuchsia.ui.views.ViewRef> focus_chain;
/// A FocusChainListener receives an updated FocusChain when focus changes.
protocol FocusChainListener {
OnFocusChange(FocusChain focus_chain) -> ();
/// A FocusChainListenerRegistry allows listening to FocusChain updates.
protocol FocusChainListenerRegistry {
Register(FocusChainListener listener);