Struct NSKeyValueSharedObservers

Source

pub struct NSKeyValueSharedObservers { /* private fields */ }

Available on crate feature NSKeyValueSharedObservers only.

Expand description

A collection of key-value observations which may be registered with multiple observable objects

Implementations§

Source §

impl NSKeyValueSharedObservers

Source

pub unsafe fn initWithObservableClass( this: Allocated<Self>, observable_class: &AnyClass, ) -> Retained<Self>

A new collection of observables for an observable object of the given class

§Safety

observable_class probably has further requirements.

Source

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

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pub unsafe fn new() -> Retained<Self>

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pub unsafe fn addSharedObserver_forKey_options_context( &self, observer: &NSObject, key: &NSString, options: NSKeyValueObservingOptions, context: *mut c_void, )

Available on crate features NSKeyValueObserving and NSString only.

Add a new observer to the collection.

This method works like -[NSObject addObserver: forKey: options: context:], but observations on nested and computed properties are disallowed. Observers are not registered until setSharedObservers is called on the observable.

Parameter observer: The observer object to register for KVO notifications. The observer must implement the key-value observing method observeValue: forKeyPath: of: change: context:
Parameter key: key of the property being observed. This cannot be a nested key path or a computed property
Parameter options: A combination of NSKeyValueObservingOptions values that specify what is included in observation notifications. For possible values see NSKeyValueObservingOptions.
Parameter context: Arbitrary data which is passed to the observer object

§Safety

observer should be of the correct type.
context must be a valid pointer or null.

Source

pub unsafe fn addObserver_forKeyPath_options_context( &self, observer: &NSObject, key_path: &NSString, options: NSKeyValueObservingOptions, context: *mut c_void, )

Available on crate features NSKeyValueObserving and NSString only.

§Safety

observer should be of the correct type.
context must be a valid pointer or null.

Source

pub fn snapshot(&self) -> Retained<NSKeyValueSharedObserversSnapshot>

A momentary snapshot of all observers added to the collection thus far, that can be assigned to an observable using -[NSObject setSharedObservers:]

Methods from Deref<Target = NSObject>§

Source

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

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());

Source

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

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

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.

Source

pub fn downcast_ref<T>(&self) -> Option<&T>
where T: DowncastTarget,

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`
    }
}