sdk/fidl/fuchsia.ui.focus/focus_chain.fidl

// 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. If
/// no View is destroyed, Scenic can still cause invalidation by raising a
/// `ZX_USER_SIGNAL_0` on the root ViewRef.
///
/// Reception. Only certain components may receive a FocusChain, as it
/// captures global information about the scene graph.
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.
[Discoverable]
protocol FocusChainListenerRegistry {
    Register(FocusChainListener listener);
};