Struct NSCollectionLayoutDimension

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

Available on crate feature UICollectionViewCompositionalLayout only.

Expand description

Apple’s documentation

Implementations§

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impl NSCollectionLayoutDimension

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pub unsafe fn fractionalWidthDimension( fractional_width: CGFloat, mtm: MainThreadMarker, ) -> Retained<Self>

Available on crate feature objc2-core-foundation only.

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pub unsafe fn fractionalHeightDimension( fractional_height: CGFloat, mtm: MainThreadMarker, ) -> Retained<Self>

Available on crate feature objc2-core-foundation only.

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pub unsafe fn absoluteDimension( absolute_dimension: CGFloat, mtm: MainThreadMarker, ) -> Retained<Self>

Available on crate feature objc2-core-foundation only.

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pub unsafe fn estimatedDimension( estimated_dimension: CGFloat, mtm: MainThreadMarker, ) -> Retained<Self>

Available on crate feature objc2-core-foundation only.

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pub unsafe fn uniformAcrossSiblingsWithEstimate( estimated_dimension: CGFloat, mtm: MainThreadMarker, ) -> Retained<Self>

Available on crate feature objc2-core-foundation only.

Items with this dimension type will receive at least as much room as the view requires, and will grow to match the dimension of the largest estimated sibling in their parent. When specified on the outermost group for a section, the largest size will be shared across the entire section.

Eg: All NSCollectionLayoutItems specified with a uniformAcrossSiblingsWithEstimate: heightDimension in a horizontal NSCollectionLayoutGroup will have a height equal to the height of the tallest item in that group.

When computing the size for a dimension of this type, the layout will need to retrieve preferred attributes for all siblings in its parent, which in UICollectionView means creating views for all dependent items. This can be very expensive, so uniformAcrossSiblingsWithEstimate should only be used in layouts where the number of dependent items is known to be relatively small.

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pub unsafe fn isEstimated(&self) -> bool

Returns YES if the receiver is estimated OR uniformAcrossSiblings.

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pub unsafe fn isUniformAcrossSiblings(&self) -> bool

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pub unsafe fn dimension(&self) -> CGFloat

Available on crate feature objc2-core-foundation only.

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`
    }
}