Struct LPMetadataProvider 

pub struct LPMetadataProvider { /* private fields */ }

Available on crate feature LPMetadataProvider only.

An object that retrieves metadata for a URL.

Use LPMetadataProvider to fetch metadata for a URL, including its title, icon, and image or video links. All properties on the resulting LPLinkMetadata instance are optional.

• Note: To enable macOS clients to fetch metadata for remote URLs, add the <doc ://com.apple.documentation/documentation/bundleresources/entitlements/com_apple_security_network_client> entitlement.

Fetch link metadata from a URL

For each metadata request, create an instance of LPMetadataProvider and call LPMetadataProvider/startFetchingMetadataForURL:completionHandler:.

In the completion handler, check the error. If your user doesn’t have a network connection, the fetch can fail. If the server doesn’t respond or is too slow, the fetch can time out. Alternatively, the app may cancel the request, or an unknown error may occur.

Otherwise, use the metadata however you want, for example, to populate the title for a table view cell.

let metadataProvider = LPMetadataProvider()
let url = URL(string: "https://www.apple.com/ipad")!

metadataProvider.startFetchingMetadata(for: url) { metadata, error in
if error != nil {
// The fetch failed; handle the error.
return
}

// Make use of fetched metadata.
}

For more information about handling errors, see LinkPresentation/LPError.

See also Apple’s documentation

Implementations

impl LPMetadataProvider

pub unsafe fn startFetchingMetadataForURL_completionHandler( &self, url: &NSURL, completion_handler: &DynBlock<dyn Fn(*mut LPLinkMetadata, *mut NSError)>, )

Available on crate features LPLinkMetadata and block2 only.

Fetches metadata for the given URL.

Call this method once per LPMetadataProvider instance. If you attempt to fetch metadata multiple times on a single LPMetadataProvider instance, it throws an error.

The completion handler executes on a background queue. Dispatch any necessary UI updates back to the main queue. When the completion handler returns, it deletes any file URLs returned in the resulting LPLinkMetadata.

Concurrency Note: 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:

 func startFetchingMetadata(for url: URL) async throws -> LPLinkMetadata

For information about concurrency and asynchronous code in Swift, see <doc ://com.apple.documentation/documentation/swift/calling-objective-c-apis-asynchronously>.

pub unsafe fn startFetchingMetadataForRequest_completionHandler( &self, request: &NSURLRequest, completion_handler: &DynBlock<dyn Fn(*mut LPLinkMetadata, *mut NSError)>, )

Available on crate features LPLinkMetadata and block2 only.

Fetches metadata for the given NSURLRequest.

Call this method once per LPMetadataProvider instance. If you attempt to fetch metadata multiple times on a single LPMetadataProvider instance, it throws an error.

The completion handler executes on a background queue. Dispatch any necessary UI updates back to the main queue. When the completion handler returns, it deletes any file URLs returned in the resulting LPLinkMetadata.

Concurrency Note: 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:

 func startFetchingMetadata(for request: URLRequest) async throws -> LPLinkMetadata

For information about concurrency and asynchronous code in Swift, see <doc ://com.apple.documentation/documentation/swift/calling-objective-c-apis-asynchronously>.

pub unsafe fn cancel(&self)

Cancels a metadata request.

This method invokes the completion handler with the error code LPErrorCode/LPErrorMetadataFetchCancelled if the request hasn’t already completed.

pub unsafe fn shouldFetchSubresources(&self) -> bool

A Boolean value indicating whether to download subresources specified by the metadata.

Subresources include the icon, image, or video. When set to false, the returned LPLinkMetadata object consists only of metadata retrieved from the main resource identified by the url passed to LPMetadataProvider/startFetchingMetadataForURL:completionHandler:.

The default value is true.

pub unsafe fn setShouldFetchSubresources(&self, should_fetch_subresources: bool)

Setter for shouldFetchSubresources.

pub unsafe fn timeout(&self) -> NSTimeInterval

The time interval after which the request automatically fails if it hasn’t already completed.

The default timeout interval is 30 seconds. If a metadata fetch takes longer than the timeout interval, the completion handler is called with the error code LPErrorCode/LPErrorMetadataFetchTimedOut.

pub unsafe fn setTimeout(&self, timeout: NSTimeInterval)

Setter for timeout.

impl LPMetadataProvider

Methods declared on superclass NSObject.

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

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

Methods from Deref<Target = NSObject>

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

Handle messages the object doesn’t recognize.

See Apple’s documentation for details.

Methods from Deref<Target = AnyObject>

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());

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.

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`
    }
}

Trait Implementations

impl AsRef<AnyObject> for LPMetadataProvider

fn as_ref(&self) -> &AnyObject

Converts this type into a shared reference of the (usually inferred) input type.

impl AsRef<LPMetadataProvider> for LPMetadataProvider

fn as_ref(&self) -> &Self

Converts this type into a shared reference of the (usually inferred) input type.

impl AsRef<NSObject> for LPMetadataProvider

fn as_ref(&self) -> &NSObject

Converts this type into a shared reference of the (usually inferred) input type.

impl Borrow<AnyObject> for LPMetadataProvider

fn borrow(&self) -> &AnyObject

Immutably borrows from an owned value.

impl Borrow<NSObject> for LPMetadataProvider

fn borrow(&self) -> &NSObject

Immutably borrows from an owned value.

impl ClassType for LPMetadataProvider

const NAME: &'static str = "LPMetadataProvider"

The name of the Objective-C class that this type represents.

type Super = NSObject

The superclass of this class.

type ThreadKind = <<LPMetadataProvider as ClassType>::Super as ClassType>::ThreadKind

Whether the type can be used from any thread, or from only the main thread.

fn class() -> &'static AnyClass

Get a reference to the Objective-C class that this type represents.

fn as_super(&self) -> &Self::Super

Get an immutable reference to the superclass.

impl Debug for LPMetadataProvider

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Deref for LPMetadataProvider

type Target = NSObject

The resulting type after dereferencing.

fn deref(&self) -> &Self::Target

Dereferences the value.

impl Hash for LPMetadataProvider

fn hash<H: Hasher>(&self, state: &mut H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl Message for LPMetadataProvider

fn retain(&self) -> Retained<Self>

where Self: Sized,

Increment the reference count of the receiver.

impl NSObjectProtocol for LPMetadataProvider

fn isEqual(&self, other: Option<&AnyObject>) -> bool

where Self: Sized + Message,

Check whether the object is equal to an arbitrary other object.

fn hash(&self) -> usize

where Self: Sized + Message,

An integer that can be used as a table address in a hash table structure.

fn isKindOfClass(&self, cls: &AnyClass) -> bool

where Self: Sized + Message,

Check if the object is an instance of the class, or one of its subclasses.

fn is_kind_of<T>(&self) -> bool

where T: ClassType, Self: Sized + Message,

👎Deprecated: use isKindOfClass directly, or cast your objects with AnyObject::downcast_ref

Check if the object is an instance of the class type, or one of its subclasses.

fn isMemberOfClass(&self, cls: &AnyClass) -> bool

where Self: Sized + Message,

Check if the object is an instance of a specific class, without checking subclasses.

fn respondsToSelector(&self, aSelector: Sel) -> bool

where Self: Sized + Message,

Check whether the object implements or inherits a method with the given selector.

fn conformsToProtocol(&self, aProtocol: &AnyProtocol) -> bool

where Self: Sized + Message,

Check whether the object conforms to a given protocol.

fn description(&self) -> Retained<NSObject>

where Self: Sized + Message,

A textual representation of the object.

fn debugDescription(&self) -> Retained<NSObject>

where Self: Sized + Message,

A textual representation of the object to use when debugging.

fn isProxy(&self) -> bool

where Self: Sized + Message,

Check whether the receiver is a subclass of the NSProxy root class instead of the usual NSObject.

fn retainCount(&self) -> usize

where Self: Sized + Message,

The reference count of the object.

impl PartialEq for LPMetadataProvider

fn eq(&self, other: &Self) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl RefEncode for LPMetadataProvider

const ENCODING_REF: Encoding = <NSObject as ::objc2::RefEncode>::ENCODING_REF

The Objective-C type-encoding for a reference of this type.

impl DowncastTarget for LPMetadataProvider

impl Eq for LPMetadataProvider