Struct AVMetadataObject

Source

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

Available on crate feature AVMetadataObject only.

Expand description

AVMetadataObject is an abstract class that defines an interface for a metadata object used by AVFoundation.

AVMetadataObject provides an abstract interface for metadata associated with a piece of media. One example is face metadata that might be detected in a picture. All metadata objects have a time, duration, bounds, and type.

The concrete AVMetadataFaceObject is used by AVCaptureMetadataOutput for face detection.

Implementations§

Source §

pub unsafe fn time(&self) -> CMTime

Available on crate feature objc2-core-media only.

The media time associated with this metadata object.

The value of this property is a CMTime associated with the metadata object. For capture, it is the time at which this object was captured. If this metadata object originates from a CMSampleBuffer, its time matches the sample buffer’s presentation time. This property may return kCMTimeInvalid.

Source

pub unsafe fn duration(&self) -> CMTime

Available on crate feature objc2-core-media only.

The media duration associated with this metadata object.

The value of this property is a CMTime representing the duration of the metadata object. If this metadata object originates from a CMSampleBuffer, its duration matches the sample buffer’s duration. This property may return kCMTimeInvalid.

Source

pub unsafe fn bounds(&self) -> CGRect

Available on crate feature objc2-core-foundation only.

The bounding rectangle of the receiver.

The value of this property is a CGRect representing the bounding rectangle of the object with respect to the picture in which it resides. The rectangle’s origin is top left. If the metadata originates from video, bounds may be expressed as scalar values from 0. - 1. If the original video has been scaled down, the bounds of the metadata object still are meaningful. This property may return CGRectZero if the metadata has no bounds.

Source

pub unsafe fn type(&self) -> Retained<AVMetadataObjectType>

An identifier for the metadata object.

The value of this property is an AVMetadataObjectType representing the type of the metadata object. Clients inspecting a collection of metadata objects can use this property to filter objects with a matching type.

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>§

Source

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`
    }
}