Struct UIUpdateActionPhase

#[repr(C)]
pub struct UIUpdateActionPhase { /* private fields */ }

Available on crate feature UIUpdateActionPhase only.

Each UI update consists of several phases which run in order, one after another. There are two phase groups - normal and low-latency. Normal phase group consists of phases from EventDispatch to CATransactionCommit. Low-latency phase group consists of phases from LowLatencyEventDispatch to LowLatencyCATransactionCommit. When phase group runs, all phases inside the group run. Phases run one after another in the specified order without exiting back into the run loop. Spinning a nested run loop inside any of the phases is not supported. For each UI update, normal phase group always runs. Low-latency phase group is optional and is off by default. It will run only when application explicitly requests low-latency event delivery. Be aware that handling low-level events is extremely demanding and only well profiled and optimized applications can benefit from it. Applications that were not designed to handle low-latency events will most likely drop frames. Also not all event types are eligible for low-latency event delivery. Currently only pencil events are low-latency eligible. This practically means that only pencil drawing and writing applications should request it. It’s acceptable to block main thread in any of the phases to wait for things that are absolutely required to proceed. When done properly, this will donate main thread priority to the thread being waited for, making it more likely to get those things in time and meet the completion deadline. Of course, extreme caution should be exercised when doing so - maximum wait time should have a hard limit on it that still allows to complete the remaining part of the UI update before completion deadline. Use of -[CAMetalLayer nextDrawable] is of a particular note - it’s not advised to use it on the main thread of the UI application as it might block main thread for one or more frames. Instead, consider calling -[CAMetalLayer nextDrawable] on the background thread and block main thread manually in one of the phases. Use small timeout that allows for UI update to proceed without a new drawable and still finish before the completion deadline.

See also Apple’s documentation

Implementations

impl UIUpdateActionPhase

pub unsafe fn new(mtm: MainThreadMarker) -> Retained<Self>

pub unsafe fn init(this: Allocated<Self>) -> Retained<Self>

pub unsafe fn afterUpdateScheduled( mtm: MainThreadMarker, ) -> Retained<UIUpdateActionPhase>

Phase that runs after UI update was scheduled and its timing information is know. This is a good place for things that only rely on UI update timing and don’t need user input events. Running at this stage allows to utilize time that otherwise would be wasted waiting for user input events to arrive. Purely time driven client side animations or non-interactive simulations should go here.

pub unsafe fn beforeEventDispatch( mtm: MainThreadMarker, ) -> Retained<UIUpdateActionPhase>

Before UIEvent and UIGestureRecognizer handlers run. Use this phase to prepare resources and data structures required to process user input events.

pub unsafe fn afterEventDispatch( mtm: MainThreadMarker, ) -> Retained<UIUpdateActionPhase>

After UIEvent and UIGestureRecognizer handlers run. Past this point, there will be no new user input events sent to the application. If low-latency event delivery was requested, more events might be dispatched in LowLatencyEventDispatch phase. Use this phase to react on application state after processing all user input events for the UI update, like starting a parallel rendering thread. Also, if your application uses extrapolation to smooth out low-rate event stream, use this phase to detect that certain events were not received to extrapolate them.

pub unsafe fn beforeCADisplayLinkDispatch( mtm: MainThreadMarker, ) -> Retained<UIUpdateActionPhase>

Before CADisplayLink callbacks run.

pub unsafe fn afterCADisplayLinkDispatch( mtm: MainThreadMarker, ) -> Retained<UIUpdateActionPhase>

After CADisplayLink callbacks run.

pub unsafe fn beforeCATransactionCommit( mtm: MainThreadMarker, ) -> Retained<UIUpdateActionPhase>

Before CATransaction is flushed.

pub unsafe fn afterCATransactionCommit( mtm: MainThreadMarker, ) -> Retained<UIUpdateActionPhase>

After CATransaction is flushed. Any changes to CoreAnimation layer tree made here (or later) will not appear on screen with the current UI update (they will go on screen with the next UI update). There are few exceptions to this rule however:

• It’s still possible to +[CATransaction commit] or +[CATransaction flush] manually which will send latest CoreAnimation layer changes to render server immediately. Doing so is not recommended as in addition to intended changes other potentially unrelated changes might be sent to the render server prematurely.
• If low-latency event dispatch will be performed, then all CoreAnimation layer tree changes that done before or during LowLatencyCATransactionCommit phase will appear on screen with this UI update.

pub unsafe fn beforeLowLatencyEventDispatch( mtm: MainThreadMarker, ) -> Retained<UIUpdateActionPhase>

Before UIEvent and UIGestureRecognizer handlers run for low-latency eligible events. This stage is off by default (skipped) and must be requested explicitly.

pub unsafe fn afterLowLatencyEventDispatch( mtm: MainThreadMarker, ) -> Retained<UIUpdateActionPhase>

After UIEvent and UIGestureRecognizer handlers run for low-latency eligible events. This stage is off by default (skipped) and must be requested explicitly.

pub unsafe fn beforeLowLatencyCATransactionCommit( mtm: MainThreadMarker, ) -> Retained<UIUpdateActionPhase>

Before CATransaction is flushed. Only runs when low-latency event dispatch was requested.

pub unsafe fn afterLowLatencyCATransactionCommit( mtm: MainThreadMarker, ) -> Retained<UIUpdateActionPhase>

After CATransaction is flushed. Only runs when low-latency event dispatch was requested. Any changes to CoreAnimation layer tree made here (or later) will not appear on screen with the current UI update.

pub unsafe fn afterUpdateComplete( mtm: MainThreadMarker, ) -> Retained<UIUpdateActionPhase>

The very end of the UI update. If there’s still time until completionDeadlineTime, it’s generally safe to do any idle opportunistic work here, like the one that was deferred from more time critical parts of the UI update. It’s also a good place to record last presented state, for things like on-screen velocity computations.

Methods from Deref<Target = NSObject>

pub fn doesNotRecognizeSelector(&self, sel: Sel) -> !

Handle messages the object doesn’t recognize.

See Apple’s documentation for details.

Methods from Deref<Target = AnyObject>

pub fn class(&self) -> &'static AnyClass

Available on crate feature UIIndirectScribbleInteraction only.

Dynamically find the class of this object.

Panics

May panic if the object is invalid (which may be the case for objects returned from unavailable init/new methods).

Example

Check that an instance of NSObject has the precise class NSObject.

use objc2::ClassType;
use objc2::runtime::NSObject;

let obj = NSObject::new();
assert_eq!(obj.class(), NSObject::class());

pub unsafe fn get_ivar<T>(&self, name: &str) -> &T

where T: Encode,

👎Deprecated: this is difficult to use correctly, use Ivar::load instead.

Available on crate feature UIIndirectScribbleInteraction only.

Use Ivar::load instead.

Safety

The object must have an instance variable with the given name, and it must be of type T.

See Ivar::load_ptr for details surrounding this.

pub fn downcast_ref<T>(&self) -> Option<&T>

where T: DowncastTarget,

Available on crate feature UIIndirectScribbleInteraction only.

Attempt to downcast the object to a class of type T.

This is the reference-variant. Use Retained::downcast if you want to convert a retained object to another type.

Mutable classes

Some classes have immutable and mutable variants, such as NSString and NSMutableString.

When some Objective-C API signature says it gives you an immutable class, it generally expects you to not mutate that, even though it may technically be mutable “under the hood”.

So using this method to convert a NSString to a NSMutableString, while not unsound, is generally frowned upon unless you created the string yourself, or the API explicitly documents the string to be mutable.

See Apple’s documentation on mutability and on isKindOfClass: for more details.

Generic classes

Objective-C generics are called “lightweight generics”, and that’s because they aren’t exposed in the runtime. This makes it impossible to safely downcast to generic collections, so this is disallowed by this method.

You can, however, safely downcast to generic collections where all the type-parameters are AnyObject.

Panics

This works internally by calling isKindOfClass:. That means that the object must have the instance method of that name, and an exception will be thrown (if CoreFoundation is linked) or the process will abort if that is not the case. In the vast majority of cases, you don’t need to worry about this, since both root objects NSObject and NSProxy implement this method.

Examples

Cast an NSString back and forth from NSObject.

use objc2::rc::Retained;
use objc2_foundation::{NSObject, NSString};

let obj: Retained<NSObject> = NSString::new().into_super();
let string = obj.downcast_ref::<NSString>().unwrap();
// Or with `downcast`, if we do not need the object afterwards
let string = obj.downcast::<NSString>().unwrap();

Try (and fail) to cast an NSObject to an NSString.

use objc2_foundation::{NSObject, NSString};

let obj = NSObject::new();
assert!(obj.downcast_ref::<NSString>().is_none());

Try to cast to an array of strings.

use objc2_foundation::{NSArray, NSObject, NSString};

let arr = NSArray::from_retained_slice(&[NSObject::new()]);
// This is invalid and doesn't type check.
let arr = arr.downcast_ref::<NSArray<NSString>>();

This fails to compile, since it would require enumerating over the array to ensure that each element is of the desired type, which is a performance pitfall.

Downcast when processing each element instead.

use objc2_foundation::{NSArray, NSObject, NSString};

let arr = NSArray::from_retained_slice(&[NSObject::new()]);

for elem in arr {
    if let Some(data) = elem.downcast_ref::<NSString>() {
        // handle `data`
    }
}

Trait Implementations

impl AsRef<AnyObject> for UIUpdateActionPhase

fn as_ref(&self) -> &AnyObject

Converts this type into a shared reference of the (usually inferred) input type.

impl AsRef<NSObject> for UIUpdateActionPhase

fn as_ref(&self) -> &NSObject

Converts this type into a shared reference of the (usually inferred) input type.

impl AsRef<UIUpdateActionPhase> for UIUpdateActionPhase

fn as_ref(&self) -> &Self

Converts this type into a shared reference of the (usually inferred) input type.

impl Borrow<AnyObject> for UIUpdateActionPhase

fn borrow(&self) -> &AnyObject

Immutably borrows from an owned value.

impl Borrow<NSObject> for UIUpdateActionPhase

fn borrow(&self) -> &NSObject

Immutably borrows from an owned value.

impl ClassType for UIUpdateActionPhase

const NAME: &'static str = "UIUpdateActionPhase"

The name of the Objective-C class that this type represents.

type Super = NSObject

The superclass of this class.

type ThreadKind = dyn MainThreadOnly

Whether the type can be used from any thread, or from only the main thread.

fn class() -> &'static AnyClass

Get a reference to the Objective-C class that this type represents.

fn as_super(&self) -> &Self::Super

Get an immutable reference to the superclass.

impl Debug for UIUpdateActionPhase

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

Formats the value using the given formatter.

impl Deref for UIUpdateActionPhase

type Target = NSObject

The resulting type after dereferencing.

fn deref(&self) -> &Self::Target

Dereferences the value.

impl Hash for UIUpdateActionPhase

fn hash<H: Hasher>(&self, state: &mut H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl Message for UIUpdateActionPhase

fn retain(&self) -> Retained<Self>

where Self: Sized,

Increment the reference count of the receiver.

impl NSObjectProtocol for UIUpdateActionPhase

fn isEqual(&self, other: Option<&AnyObject>) -> bool

where Self: Sized + Message,

Check whether the object is equal to an arbitrary other object.

fn hash(&self) -> usize

where Self: Sized + Message,

An integer that can be used as a table address in a hash table structure.

fn isKindOfClass(&self, cls: &AnyClass) -> bool

where Self: Sized + Message,

Check if the object is an instance of the class, or one of its subclasses.

fn is_kind_of<T>(&self) -> bool

where T: ClassType, Self: Sized + Message,

👎Deprecated: use isKindOfClass directly, or cast your objects with AnyObject::downcast_ref

Check if the object is an instance of the class type, or one of its subclasses.

fn isMemberOfClass(&self, cls: &AnyClass) -> bool

where Self: Sized + Message,

Check if the object is an instance of a specific class, without checking subclasses.

fn respondsToSelector(&self, aSelector: Sel) -> bool

where Self: Sized + Message,

Check whether the object implements or inherits a method with the given selector.

fn conformsToProtocol(&self, aProtocol: &AnyProtocol) -> bool

where Self: Sized + Message,

Check whether the object conforms to a given protocol.

fn description(&self) -> Retained<NSObject>

where Self: Sized + Message,

A textual representation of the object.

fn debugDescription(&self) -> Retained<NSObject>

where Self: Sized + Message,

A textual representation of the object to use when debugging.

fn isProxy(&self) -> bool

where Self: Sized + Message,

Check whether the receiver is a subclass of the NSProxy root class instead of the usual NSObject.

fn retainCount(&self) -> usize

where Self: Sized + Message,

The reference count of the object.

impl PartialEq for UIUpdateActionPhase

fn eq(&self, other: &Self) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl RefEncode for UIUpdateActionPhase

const ENCODING_REF: Encoding = <NSObject as ::objc2::RefEncode>::ENCODING_REF

The Objective-C type-encoding for a reference of this type.

impl DowncastTarget for UIUpdateActionPhase

impl Eq for UIUpdateActionPhase