ios 无法从 Objective-C 访问 Swift 4 类：“在类型对象上找不到属性”
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Unable to access Swift 4 class from Objective-C: "Property not found on object of type"
提问by Doug Smith
Using the latest Xcode 9 beta, I'm seemingly completely unable to access properties on Swift classes. Even odder, I can access the class itself to instantiate it or whatever, but completely unable to access properties on it.
使用最新的 Xcode 9 beta，我似乎完全无法访问 Swift 类的属性。更奇怪的是，我可以访问类本身来实例化它或其他什么，但完全无法访问它的属性。
So if I have this Swift class:
所以如果我有这个 Swift 类：
import UIKit
class TestViewController: UIViewController {
var foobar = true
}
And I try to do this:
我尝试这样做：
TestViewController *testViewController = [[TestViewController alloc] init]; // success
testViewController.foobar; // error
What exactly am I doing wrong? New project with Xcode 9.
我到底做错了什么？使用 Xcode 9 的新项目。
回答by Paulo Mattos
The rules for exposing Swift code to Objective-C have changed in Swift 4. Try this instead:
将 Swift 代码暴露给 Objective-C 的规则在 Swift 4 中发生了变化。试试这个：
@objc var foobar = true
As an optimization, @objcinference have been reduced in Swift 4. For instance, a property within an NSObject-derived class, such as your TestViewController, will nolonger infer @objcby default (as it did in Swift 3).
作为一种优化，@objc推断已在斯威夫特4.减少举例来说，财产的范围内NSObject派生类，如你TestViewController，会不会再想见@objc在默认情况下（因为它在斯威夫特3一样）。
Alternatively, you could also expose allmembers to Objective-C at once using @objcMembers:
或者，您也可以使用以下命令一次性将所有成员公开给 Objective-C @objcMembers：
@objcMembers class TestViewController: UIViewController {
...
}
This new design is fully detailed in the corresponding Swift Evolution proposal.
这个新设计在相应的 Swift Evolution 提案中有完整的细节。
回答by ingconti
Swift 3.2/4.0 / XCode 9.1
斯威夫特 3.2/4.0 / XCode 9.1
You you set swift3.2 in project settings ( //:configuration = Debug SWIFT_VERSION = 3.2)
您在项目设置中设置 swift3.2 ( //:configuration = Debug SWIFT_VERSION = 3.2)
you can use your code,(using the correct import file in objc, see below). If You set project to swift 4.0 ( //:configuration = Debug SWIFT_VERSION = 4.0)
你可以使用你的代码，（在 objc 中使用正确的导入文件，见下文）。如果您将项目设置为 swift 4.0 ( //:configuration = Debug SWIFT_VERSION = 4.0)
You must prepend @objc for every property.
您必须为每个属性添加 @objc。
So:
所以：
Swift 3.2:
斯威夫特 3.2：
// MyClass.swift
@objc class MyClass: NSObject{
var s1: String?
@objc var s2 : String?
}
//
// ViewController.m
import "MixingObjCAndSwift-Swift.h"
#import "ViewController.h"
@interface ViewController ()
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
MyClass * mc = [MyClass new];
NSString * s1 = mc.s1;
NSString * s2 = mc.s2;
}
works.
作品。
Swift 4.0:
斯威夫特 4.0：
// MyClass.swift
@objc class MyClass: NSObject{
var s1: String?
@objc var s2 : String?
}
.....
- (void)viewDidLoad {
[super viewDidLoad];
MyClass * mc = [MyClass new];
NSString * s1 = mc.s1;
NSString * s2 = mc.s2;
}
does NOT works: compiler fails:
不起作用：编译器失败：
/Users....ViewController.m:24:21: Property 's1' not found on object of type 'MyClass *'
/Users....ViewController.m:24:21: 在“MyClass *”类型的对象上找不到属性“s1”
as s1 is not prepended with @objc.
因为 s1 前面没有@objc。
You must write:
你必须写：
@objc class MyClass: NSObject{
@objc var s1: String?
@objc var s2 : String?
}
(As a side-note: in C/C++/ObJC file, put always system/general *h files before your "local" class headers.)
（附带说明：在 C/C++/ObJC 文件中，始终将 system/general *h 文件放在“本地”类头文件之前。）
Swift 4
斯威夫特 4
just add @objcMembers before class @objcMembersclass MyClassObject: NSObject { var s1: String! var s2: String!
只需在@objcMembers类之前添加 @objcMembers 类 MyClassObject: NSObject { var s1: String! var s2：字符串！
} Swift evolutionenter link description here
Swift 进化在这里输入链接描述
回答by protspace
As for Swift 5.1 I found that "@objc" is not enough, but also make it public "@objc public":
至于Swift 5.1，我发现“@objc”还不够，还要公开“@objc public”：
@objc public class SomeClass: NSObject {
@objc public let amount: NSNumber
...
回答by Rahul Kumar
- When you add a swift file in your Objective-C project, Xcode will prompt to add Objective-C bridging headerfile, so allow the header file to be created.
- In your Objective-C implementation file where you want to access the TestViewController property foobar. Use the following import syntax and replace the ProjectName with your project.
- 当您在 Objective-C 项目中添加 swift 文件时，Xcode 会提示添加Objective-C 桥接头文件，因此允许创建头文件。
- 在您想要访问 TestViewController 属性foobar 的Objective-C 实现文件中。使用以下导入语法并将 ProjectName 替换为您的项目。
#import "ProjectName-Swift.h"
#import "ProjectName-Swift.h"
Objective-C implementation file:
Objective-C 实现文件：
#import "ViewController.h"
#import "ProjectName-Swift.h"
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
TestViewController *testViewController = [[TestViewController alloc] init]; // success
BOOL prop = testViewController.foobar;
NSLog(@"Property: %d", prop);
}
@end
For more details go through the Apple Documents
有关更多详细信息，请参阅Apple 文档
回答by P Anandhakumar
Xcode 10.2 | Swift 4Adding @objcMembersbefore class solved my problem.
Xcode 10.2 | Swift 4添加@objcMembers课前解决了我的问题。
@objcMembers class MyClass:NSObject {
var s1: String!
var s2: NSMutableArray!
}
回答by Prabhat Kasera
I also encountered with this problem in swift 3.0
我在 swift 3.0 中也遇到过这个问题
class declaration was like that
类声明就是这样
class ClassA {
//statements
}
above class was not accessible in Objective C code and it was also not registered in -Swift.h
上面的类在 Objective C 代码中无法访问，也没有在 -Swift.h 中注册
once I inherited from NSObject like this:
一旦我像这样从 NSObject 继承：
class ClassA : NSObject {
//statements
}
the class was accessible in Objective c and got registered with -Swift.h
该类可以在 Objective c 中访问并注册到 -Swift.h
This solution is useful when you don't want to avoid inheritance from NSobject class.
当您不想避免从 NSobject 类继承时，此解决方案很有用。
