Enum ViewRefFocusedRequest

pub enum ViewRefFocusedRequest {
    Watch {
        responder: ViewRefFocusedWatchResponder,
    },
}

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.

Variants

Watch

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.

Fields

responder: ViewRefFocusedWatchResponder

Implementations

impl ViewRefFocusedRequest

pub fn into_watch(self) -> Option<ViewRefFocusedWatchResponder>

pub fn method_name(&self) -> &'static str

Name of the method defined in FIDL

Trait Implementations

impl Debug for ViewRefFocusedRequest

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.