Struct UIFocusUpdateContext

Source

pub struct UIFocusUpdateContext { /* private fields */ }

Available on crate feature UIFocus only.

Expand description

UIFocusUpdateContexts provide information relevant to a specific focus update from one view to another. They are ephemeral objects that are usually discarded after the update is finished.

Implementations§

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impl UIFocusUpdateContext

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pub fn previouslyFocusedItem( &self, ) -> Option<Retained<ProtocolObject<dyn UIFocusItem>>>

The item that was focused before the update, i.e. where focus is updating from. May be nil if no item was focused, such as when focus is initially set.

Source

pub fn nextFocusedItem( &self, ) -> Option<Retained<ProtocolObject<dyn UIFocusItem>>>

The item that is focused after the update, i.e. where focus is updating to. May be nil if no item is being focused, meaning focus is being lost.

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pub fn focusHeading(&self) -> UIFocusHeading

The focus heading in which the update is occurring.

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impl UIFocusUpdateContext

Methods declared on superclass NSObject.

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

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

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impl UIFocusUpdateContext

UIKitAdditions.

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pub fn previouslyFocusedView(&self) -> Option<Retained<UIView>>

Available on crate features UIFocusUpdateContext_UIKitAdditions and UIResponder and UIView only.

The view that was focused before the update. May be nil if no view was focused, such as when setting initial focus. If previouslyFocusedItem is not a view, this returns that item’s containing view, otherwise they are equal. NOTE: This property will be deprecated in a future release. Use previouslyFocusedItem instead.

Source

pub fn nextFocusedView(&self) -> Option<Retained<UIView>>

Available on crate features UIFocusUpdateContext_UIKitAdditions and UIResponder and UIView only.

The view that will be focused after the update. May be nil if no view will be focused. If nextFocusedItem is not a view, this returns that item’s containing view, otherwise they are equal. NOTE: This property will be deprecated in a future release. Use nextFocusedItem instead.

Methods from Deref<Target = NSObject>§

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

Handle messages the object doesn’t recognize.

See Apple’s documentation for details.

Methods from Deref<Target = AnyObject>§

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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());

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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.

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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`
    }
}