Struct SHSignatureGenerator

Source

pub struct SHSignatureGenerator { /* private fields */ }

Available on crate feature SHSignatureGenerator only.

Expand description

An object for converting audio data into a signature.

Create both reference and query signatures using this class.

Implementations§

Source §

impl SHSignatureGenerator

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pub unsafe fn generateSignatureFromAsset_completionHandler( asset: &AVAsset, completion_handler: &DynBlock<dyn Fn(mut SHSignature, mut NSError)>, )

Available on crate features SHSignature and block2 and objc2-av-foundation only.

Creates a signature with the asset you specify.

Important: You can call this method from synchronous code using a completion handler, as shown on this page, or you can call it as an asynchronous method that has the following declaration:
class func signature(from asset: AVAsset) async throws -> SHSignature
For information about concurrency and asynchronous code in Swift, see <doc ://com.apple.documentation/documentation/swift/calling-objective-c-apis-asynchronously>.

The asset you specify can be any type of media that contains audio tracks. If the asset has multiple tracks, the system mixes them into one SHSignature.

Parameters:
asset: An asset that contains the audio to convert.
completionHandler: The system calls this completion block after creating the signature, or an error if the system couldn’t create it.

This block takes the following parameters:

term signature: A new signature instance.
term error: An error object if a problem occurs when creating thesignature; otherwise, nil.

Source

pub unsafe fn appendBuffer_atTime_error( &self, buffer: &AVAudioPCMBuffer, time: Option<&AVAudioTime>, ) -> Result<(), Retained<NSError>>

Available on crate feature objc2-avf-audio only.

Adds audio to the generator.

Using noncontiguous audio may result in a lower-quality signature.

The audio must be PCM at one of these rates:

48000 hertz
44100 hertz
32000 hertz
16000 hertz
Parameters:
buffer: The audio data to append to the signature generator.
time: The time position of the start of the audio buffer in the full audio you use to generate the signature.
error: The error that occurs; otherwise, nil.

Source

pub unsafe fn signature(&self) -> Retained<SHSignature>

Available on crate feature SHSignature only.

Converts the audio buffer into a signature.

Returns: A signature that ShazamKit generates from the audio buffer.

Source §

impl SHSignatureGenerator

Methods declared on superclass NSObject.

Source

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

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

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

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`
    }
}