如何注释在Swift中使用的Objective-C API(例如返回类型) [英] How to annotate Objective-C APIs for use in Swift (e.g. return types)

问题描述

根据Xcode发行说明，Apple一直在审核"其现有API，以删除隐式解包的可选控件.这意味着它们的API会在适当的情况下返回T或T?而不是T!.

According to the Xcode release notes, Apple has been "auditing" their existing APIs to remove implicitly unwrapped optionals. That means that instead of T!, their APIs will return T or T? where appropriate.

他们在哪里做?如何注释/包装现有的Objective-C代码(尤其是库)，使其更易于在Swift中使用?

Where do they do this? How can I annotate/wrap my existing Objective-C code (especially libraries) to make it cleaner to use from Swift?

推荐答案

Xcode 6.3/Swift 1.2

Xcode 6.3新增了对在Objective-C中注释可空性的官方支持.

Xcode 6.3/Swift 1.2

Xcode 6.3 added official support for annotating nullability in Objective-C.

可以通过使用关键字__nullable，__nonnull和__null_unspecified(默认值)注释类型来声明值的可空性.在属性和方法中，关键字为nullable，nonnull和null_unspecified.

The nullability of a value can be declared by annotating the type with the keywords __nullable, __nonnull and __null_unspecified (the default). In properties and methods the keywords are nullable, nonnull and null_unspecified.

Xcode发行说明中的​​示例

Examples from the Xcode release notes

   - (void)registerNib:(nonnull UINib *)nib
forCellReuseIdentifier:(nonnull NSString *)identifier;

- (nullable UITableViewCell *)cellForRowAtIndexPath:(nonnull NSIndexPath)indexPath;

@property (nonatomic, readwrite, retain, nullable) UIView *backgroundView;

更改默认值

null_unspecified(转换为T!)是所有现有代码的默认设置.一项有用的功能是可以更改API部分的默认设置.

Changing the default

null_unspecified (which translates to T!) is the default for all existing code. A useful feature is the ability to change the default for sections of your API.

NS_ASSUME_NONNULL_BEGIN
// nonnull is the default here
NS_ASSUME_NONNULL_END

这消除了很多噪音，因为接受和处理nil的方法通常是例外，而不是规则.就个人而言，我会将其用于所有审核的API.

This removes a lot of noise, since methods that accept and handle nil usually are the exception, not the rule. Personally, I would use this for all audited APIs.

null_resettable是一个附加注释，用于不常见的情况，在这种情况下，您可以将属性设置为nil，但永远不会 nil(因为它会重置设置为默认值).

null_resettable is an additional annotation that is used for the uncommon case where you can set a property to nil, but it will never be nil (because it resets to a default value).

 @property (nonatomic, retain, null_resettable) UIColor *tintColor;

就个人而言，对于新代码，我会避免这种行为.这种属性的混合性质不适用于Swift.

Personally, I would avoid this behavior for new code. The hybrid nature of such properties isn't a good fit for Swift.

Xcode 7添加了对在Objective-C中注释泛型类型的支持.

Xcode 7 adds support for annotating generic types in Objective-C.

NSArray，NSSet和NSDictionary(它们自动桥接到Swift的Array，Set和Dictionary)可以用其内容类型进行注释.

NSArray, NSSet and NSDictionary (which are automatically bridged to Swift's Array, Set and Dictionary can be annotated with the type of their contents.

@property NSArray<NSString *> *stringArray;
@property NSSet<NSString *> *stringSet;
@property NSDictionary<NSString *, NSString *> *stringDict;

还有一个__kindof关键字，它告诉Objective-C编译器不太严格，允许向下转换.但这并不影响Swift方面.

There's also the __kindof keyword that tells the Objective-C compiler to be less strict and allow downcasting. But it doesn't affect the Swift side.

@interface MyArray1<__covariant T> : NSObject
- (void)addObject:(T)object;
@end

@interface MyArray2<__covariant T : NSObject *> : NSObject
- (void)addObject:(T)object;
@end

@interface MyArray3<__covariant T : id<NSCopying>> : NSObject
- (void)addObject:(T)object;
@end

@implementation不了解T，因此像往常一样使用id/NSObject */id<NSCopying>.

The @implementation doesn't know about T and uses id/NSObject */id<NSCopying> as it always did.

这篇关于如何注释在Swift中使用的Objective-C API(例如返回类型)的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！