class ViewRefFocused
Defined at line 2196 of file fidling/gen/sdk/fidl/fuchsia.ui.views/fuchsia.ui.views/hlcpp/fuchsia/ui/views/cpp/fidl.h
A method of enabling a ViewRef creator to determine if its ViewRef has
gained or lost focus in the view tree.
The protocol client has implicit access to the ViewRef it created; the
protocol itself does not accept a ViewRef parameter. Clients, both trusted
or otherwise, need access to view-focus state, so the protocol is
deliberately minimal. Possession of a ViewRef (and this protocol) does not
grant the power to learn about a ViewRef's focus state.
Public Methods
void ~ViewRefFocused ()void Watch (WatchCallback callback)Sets up a callback to fire when the implicit ViewRef has gained or lost
focus. Typically, focus changes happen at a slow pace, such that every
transition is captured by the callback. However, focus changes can
happen rapidly, so the callback may "compress" focus change history into
just the latest known focus state.
The callback reports the last focus change spanning the duration from
its issuance to the previous callback's issuance. The client may observe
any of the following four transitions:
- true -> true: The ViewRef has lost focus at least once, and has gained
focus by the time of callback issuance.
- true -> false: The ViewRef has lost focus at least once, and has lost
focus by the time of callback issuance.
- false -> true: The ViewRef has gained focus at least once, and has
gained focus by the time of callback issuance.
- false -> false: The ViewRef has gained focus at least once, and has
lost focus by the time of callback issuance.
The client avoids "focus flapping" and always sees the latest state.
Every callback issuance is meaningful, and the client should renegotiate
focus-related services appropriately, such as IME.
Flow control: The caller is allowed at most one in-flight |Watch| call
at at time: subsequent |Watch| calls must wait until the acknowledgment
returns. Non-compliance results in channel closure.