ios 指针缺少可空性类型说明符

Pointer is missing a nullability type specifier

提问by kelin

In Xcode 7 GM I started to get this warning:

在 Xcode 7 GM 中，我开始收到此警告：

Pointer is missing a nullability type specifier (_Nonnull, _Nullable, or _Null_unspecified)

指针缺少可空性类型说明符（_Nonnull、_Nullable 或 _Null_unspecified）

In the following function declaration (NSUserDefaults extension)

在下面的函数声明中（NSUserDefaults 扩展）

- (void)setObject:(nullable id)value
           forKey:(NSString *)defaultName
    objectChanged:(void(^)(NSUserDefaults *userDefaults, id value))changeHandler
    objectRamains:(void(^)(NSUserDefaults *userDefaults, id value))remainHandler;

Why this warning is showing and how should I fix it?

为什么会显示此警告，我该如何解决？

采纳答案by Ares

You need to specify nullablealso for the handlers/blocks

您还需要nullable为处理程序/块指定

- (void)setObject:(nullable id)value
           forKey:(nonnull NSString *)defaultName
    objectChanged:(nullable void(^)(NSUserDefaults *userDefaults, id value))changeHandler
    objectRamains:(nullable void(^)(NSUserDefaults *userDefaults, id value))remainHandler;

Why? It's due to Swift. Swift allows optional parameters (?), which Objective-C does not. This is done as a bridge between the both of them for the Swift compiler to know those parameters are optional. A 'Nonnull' will tell the Swift compiler that the argument is the required. A nullable that it is optional

为什么？这是由于斯威夫特。Swift 允许可选参数 (?)，而 Objective-C 则不允许。这是作为两者之间的桥梁，以便 Swift 编译器知道这些参数是可选的。'Nonnull' 将告诉 Swift 编译器该参数是必需的。一个可空的，它是可选的

For more info read: https://developer.apple.com/swift/blog/?id=25

欲了解更多信息，请阅读：https: //developer.apple.com/swift/blog/?id=25

回答by Kevin

You can use the following macros around blocks of declarations (functions and variables) in objective c headers:

您可以在目标 c 标头中的声明块（函数和变量）周围使用以下宏：

NS_ASSUME_NONNULL_BEGIN 

NS_ASSUME_NONNULL_END

You need to then add nullable annotations for references that can be nil within that block. This applies to both function parameters and variable declarations.

然后，您需要为该块中可能为零的引用添加可为空的注释。这适用于函数参数和变量声明。

As in:

如：

@interface SMLBaseUserDetailsVC : UIViewController < UICollectionViewDelegate>
NS_ASSUME_NONNULL_BEGIN

@property (nonatomic, readonly) IBOutlet UIScrollView *detailsScrollView;
@property (nonatomic, readonly) IBOutlet UICollectionView *photoCV;
@property (nonatomic, weak, readonly) SMLUser *user;
- (IBAction)flagUser:(id)sender;
- (IBAction)closeAction:(nullable id)sender;
- (void) prefetchPhotos;

NS_ASSUME_NONNULL_END

@end

Edit* The why??? is because for an objective-c class to be interoperable with swift, you need to declare nullability so that the compiler knows to treat properties as swift optionals or not. Nullable objective c properties are known as optionals in swift and using these macros in conjunction with the nullable declarators for properties allows the compiler to treat them as optionals (Optionals are monads - an object that wraps up either the object or nil).

编辑* 为什么？？？是因为对于要与 swift 互操作的 Objective-c 类，您需要声明可空性，以便编译器知道是否将属性视为 swift 可选。可空的目标 c 属性在 swift 中被称为可选项，将这些宏与属性的可空声明符结合使用允许编译器将它们视为可选项（可选项是 monads - 一个包含对象或 nil 的对象）。

回答by kelin

The correct, working method declaration, accepted by compiler:

编译器接受的正确的工作方法声明：

- (void)setObject:(nullable id)value
           forKey:(nonnull NSString *)defaultName
    objectChanged:(nullable void(^)(NSUserDefaults *_Nonnull userDefaults, id _Nullable value))changeHandler
    objectRamains:(nullable void(^)(NSUserDefaults *_Nonnull userDefaults, id _Nullable value))remainHandler;

回答by fishtrees

I post this answer to tell why should add _Nonnullor nullable.

我发布此答案是为了说明为什么要添加_Nonnull或nullable。

According to this blog: https://developer.apple.com/swift/blog/?id=25

根据这个博客：https: //developer.apple.com/swift/blog/?id=25

One of the great things about Swift is that it transparently interoperates with Objective-C code, both existing frameworks written in Objective-C and code in your app. However, in Swift there's a strong distinction between optional and non-optional references, e.g. NSViewvs. NSView?, while Objective-C represents boths of these two types as NSView *. Because the Swift compiler can't be sure whether a particular NSView *is optional or not, the type is brought into Swift as an implicitly unwrapped optional, NSView!.

Swift 的一大优点是它可以与 Objective-C 代码透明地互操作，现有的框架都是用 Objective-C 编写的，也可以是你的应用程序中的代码。然而，在 Swift 中，可选引用和非可选引用之间有很大的区别，例如NSViewvs. NSView?，而 Objective-C 将这两种类型都表示为NSView *. 因为 Swift 编译器不能确定一个特定的是否NSView *是可选的，所以该类型作为一个隐式解包的可选NSView!.

it's all for Swift.

这一切都是为了 Swift。

回答by Albert Renshaw

To disable this warning across your entire project

在整个项目中禁用此警告

1. Go to Build Settings

2. Make sure you are viewing the "All" tab not "Basic" or "Customized"

3. Search for the field Other Warning Flags

4. Add the following flag: -Wno-nullability-completeness.

5. Now clean and build (cmd+shift+k then cmd+r)

6. Quit xCode and Re-open (Don't skip this step!)

   --note, it can take a few seconds for the warnings to go away even after you finish building and relaunching xCode, for me it takes about 15 seconds for xCode to fully update

1. 转到构建设置

2. 确保您查看的是“全部”选项卡，而不是“基本”或“自定义”

3. 搜索领域 Other Warning Flags

4. 添加以下标志：-Wno-nullability-completeness.

5. 现在清理并构建（cmd+shift+k 然后 cmd+r）

6. 退出 xCode 并重新打开（不要跳过这一步！）

   --注意，即使在您完成构建和重新启动 xCode 后，警告消失也可能需要几秒钟，对我而言，xCode 完全更新需要大约 15 秒

回答by dilip

Remove below macro from your .h file and warning will disappear

从您的 .h 文件中删除以下宏，警告将消失

NS_ASSUME_NONNULL_BEGIN 

NS_ASSUME_NONNULL_END