本文翻译自：How do I call Objective-C code from Swift?

In Swift, how does one call Objective-C code? 在Swift中，如何调用Objective-C代码？

Apple mentioned that they could co-exist in one application, but does this mean that one could technically re-use old classes made in Objective-C whilst building new classes in Swift? 苹果公司提到它们可以在一个应用程序中共存，但这是否意味着在技术上可以重复使用由Objective-C创建的旧类，同时在Swift中构建新类呢？

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参考：https://stackoom.com/question/1ci6z/如何从Swift调用Objective-C代码

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See Apple's guide to Using Swift with Cocoa and Objective-C . 请参阅Apple关于将Swift与Cocoa和Objective-C结合使用的指南。 This guide covers how to use Objective-C and C code from Swift and vice versa and has recommendations for how to convert a project or mix and match Objective-C/C and Swift parts in an existing project. 本指南涵盖了如何使用Swift中的Objective-C和C代码，反之亦然，并提供了有关如何转换项目或在现有项目中混合和匹配Objective-C / C和Swift部件的建议。

The compiler automatically generates Swift syntax for calling C functions and Objective-C methods. 编译器自动生成用于调用C函数和Objective-C方法的Swift语法。 As seen in the documentation, this Objective-C: 如文档所示，此Objective-C：

UITableView *myTableView = [[UITableView alloc] initWithFrame:CGRectZero style:UITableViewStyleGrouped];

turns into this Swift code: 变成以下Swift代码：

let myTableView: UITableView = UITableView(frame: CGRectZero, style: .Grouped)

Xcode also does this translation on the fly — you can use Open Quickly while editing a Swift file and type an Objective-C class name, and it'll take you to a Swift-ified version of the class header. Xcode也可以即时进行翻译-您可以在编辑Swift文件时使用“快速打开”并键入Objective-C类名称，然后它将带您到类头的Swift版本。 (You can also get this by cmd-clicking on an API symbol in a Swift file.) And all the API reference documentation in the iOS 8 and OS X v10.10 (Yosemite) developer libraries is visible in both Objective-C and Swift forms (eg UIView ). （您也可以通过cmd单击Swift文件中的API符号来获取此信息。） iOS 8和OS X v10.10（Yosemite）开发人员库中的所有API参考文档在Objective-C和Swift中都可见表单（例如UIView ）。

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Quote from the documentation : 从文档引用：

Any Objective-C framework (or C library) that's accessible as a module can be imported directly into Swift. 任何可作为模块访问的Objective-C框架（或C库）都可以直接导入到Swift中。 This includes all of the Objective-C system frameworks—such as Foundation, UIKit, and SpriteKit—as well as common C libraries supplied with the system. 这包括所有的Objective-C系统框架（例如Foundation，UIKit和SpriteKit），以及系统随附的通用C库。 For example, to import Foundation, simply add this import statement to the top of the Swift file you're working in: 例如，要导入Foundation，只需将此导入语句添加到您正在使用的Swift文件的顶部：

import Foundation

This import makes all of the Foundation APIs—including NSDate, NSURL, NSMutableData, and all of their methods, properties, and categories—directly available in Swift. 此导入使所有Foundation API（包括NSDate，NSURL，NSMutableData及其所有方法，属性和类别）都可以直接在Swift中使用。

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Using Objective-C Classes in Swift 在Swift中使用Objective-C类

** If you have an existing class that you'd like to use, perform Step 2 and then skip to Step 5 . **如果您有想要使用的现有课程，请执行步骤2 ，然后跳到步骤5 。 (For some cases, I had to add an explicit #import <Foundation/Foundation.h to an older Objective-C File.) ** （在某些情况下，我必须在旧的Objective-C文件中添加一个明确的#import <Foundation/Foundation.h 。）**

Step 1: Add Objective-C Implementation -- .m 步骤1：添加Objective-C实施-.m

Add a .m file to your class, and name it CustomObject.m . 将.m文件添加到您的类中，并将其命名为CustomObject.m 。

Step 2: Add Bridging Header 步骤2：添加桥接标题

When adding your .m file, you'll likely be hit with a prompt that looks like this: 添加.m文件时，可能会出现类似以下提示的提示：

Click YES ! 点击是！

If you did not see the prompt, or accidentally deleted your bridging header, add a new .h file to your project and name it <#YourProjectName#>-Bridging-Header.h . 如果您没有看到提示，或者不小心删除了桥接标题，请向您的项目中添加一个新的.h文件，并将其命名为<#YourProjectName#>-Bridging-Header.h 。

In some situations, particularly when working with Objective-C frameworks, you don't add an Objective-C class explicitly and Xcode can't find the linker. 在某些情况下，尤其是在使用Objective-C框架时，您无需显式添加Objective-C类，并且Xcode找不到链接器。 In this case, create your .h file named as mentioned above, then make sure you link its path in your target's project settings like so: 在这种情况下，创建如上所述的.h文件，然后确保将其路径链接到目标的项目设置中，如下所示：

Note 注意

It's best practice to link your project using the $(SRCROOT) macro so that if you move your project, or work on it with others using a remote repository, it will still work. 最佳实践是使用$(SRCROOT)宏链接项目，以便在移动项目或使用远程存储库与其他项目一起使用时，该项目仍然有效。 $(SRCROOT) can be thought of as the directory that contains your .xcodeproj file. $(SRCROOT)可以认为是包含.xcodeproj文件的目录。 It might look like this: 它可能看起来像这样：

$(SRCROOT)/Folder/Folder/<#YourProjectName#>-Bridging-Header.h

Step 3: Add Objective-C Header -- .h 步骤3：添加Objective-C标头-.h

Add another .h file and name it CustomObject.h . 添加另一个.h文件，并将其命名为CustomObject.h 。

Step 4: Build your Objective-C Class 步骤4：建立您的Objective-C类

In CustomObject.h 在CustomObject.h

#import <Foundation/Foundation.h>@interface CustomObject : NSObject@property (strong, nonatomic) id someProperty;- (void) someMethod;@end

In CustomObject.m 在CustomObject.m

#import "CustomObject.h"@implementation CustomObject - (void) someMethod {NSLog(@"SomeMethod Ran");
}@end

Step 5: Add Class to Bridging-Header 步骤5：将类添加到Bridging-Header

In YourProject-Bridging-Header.h : 在YourProject-Bridging-Header.h ：

#import "CustomObject.h"

Step 6: Use your Object 步骤6：使用您的对象

In SomeSwiftFile.swift : 在SomeSwiftFile.swift ：

var instanceOfCustomObject: CustomObject = CustomObject()
instanceOfCustomObject.someProperty = "Hello World"
println(instanceOfCustomObject.someProperty)
instanceOfCustomObject.someMethod()

There is no need to import explicitly; 无需显式导入； that's what the bridging header is for. 这就是桥接头的用途。

Using Swift Classes in Objective-C 在Objective-C中使用Swift类

Step 1: Create New Swift Class 步骤1：建立新的Swift类别

Add a .swift file to your project, and name it MySwiftObject.swift . 将一个.swift文件添加到您的项目中，并将其命名为MySwiftObject.swift 。

In MySwiftObject.swift : 在MySwiftObject.swift ：

import Foundationclass MySwiftObject : NSObject {var someProperty: AnyObject = "Some Initializer Val"init() {}func someFunction(someArg:AnyObject) -> String {var returnVal = "You sent me \(someArg)"return returnVal}
}

Step 2: Import Swift Files to ObjC Class 步骤2：将Swift文件导入ObjC类

In SomeRandomClass.m : 在SomeRandomClass.m ：

#import "<#YourProjectName#>-Swift.h"

The file: <#YourProjectName#>-Swift.h should already be created automatically in your project, even if you can not see it. 即使您看不到文件，也已经在您的项目中自动创建了文件<#YourProjectName#>-Swift.h 。

Step 3: Use your class 步骤3：使用课堂

MySwiftObject * myOb = [MySwiftObject new];
NSLog(@"MyOb.someProperty: %@", myOb.someProperty);
myOb.someProperty = @"Hello World";
NSLog(@"MyOb.someProperty: %@", myOb.someProperty);// original
NSString * retString = [myOb someFunction:@"Arg"];
// xcode10 expands the external arg here
NSString * retString = [myOb someFunctionWithSomeArg:@"Arg"];|NSLog(@"RetString: %@", retString);

Note: 注意：

1. CodeCompletion wasn't behaving as accurately as I'd like it to. 1. CodeCompletion的行为不如我希望的那样准确。 On my system, running a quick build with "cmd + r" seemed to help Swift find some of the Objective-C code and vice versa. 在我的系统上，使用“ cmd + r”运行快速构建似乎可以帮助Swift查找一些Objective-C代码，反之亦然。

2. If you add a .swift file to an older project and get error: dyld: Library not loaded: @rpath/libswift_stdlib_core.dylib , try completely restarting Xcode . 2.如果将.swift文件添加到较旧的项目中并出现错误： dyld: Library not loaded: @rpath/libswift_stdlib_core.dylib ，请尝试完全重新启动Xcode 。

3. While it was originally possible to use pure Swift classes in Objective-C by using the @objc prefix, after Swift 2.0, this is no longer possible. 3.虽然最初可以通过使用@objc前缀在Objective-C中使用纯Swift类，但是在Swift 2.0之后，这不再可行。 See edit history for original explanation. 有关原始说明，请参见编辑历史记录。 If this functionality is reenabled in future Swift versions, the answer will be updated accordingly. 如果在以后的Swift版本中重新启用了此功能，则答案将相应更新。

#5楼

You can read the nice post Swift & Cocoapods . 您可以阅读Swift＆Cocoapods的精彩文章。 Basically, we need to create a bridging header file and put all Objective-C headers there. 基本上，我们需要创建一个桥接头文件，并将所有的Objective-C头文件放置在那里。 And then we need to reference it from our build settings. 然后我们需要从构建设置中引用它。 After that, we can use the Objective-C code. 之后，我们可以使用Objective-C代码。

let manager = AFHTTPRequestOperationManager()
manager.GET("http://example.com/resources.json",parameters: nil,success: { (operation: AFHTTPRequestOperation!,responseObject: AnyObject!) inprintln("JSON: " + responseObject.description)},failure: { (operation: AFHTTPRequestOperation!,error: NSError!) inprintln("Error: " + error.localizedDescription)})

Also have a look at Apple's document Using Swift with Cocoa and Objective-C as well. 也可以看看苹果的文档《 将Swift与Cocoa和Objective-C结合使用 》。

#6楼

I wrote a simple Xcode 6 project that shows how to mix C++, Objective-C and Swift code: 我写了一个简单的Xcode 6项目，展示了如何混合C ++，Objective-C和Swift代码：

https://github.com/romitagl/shared/tree/master/C-ObjC-Swift/Performance_Console https://github.com/romitagl/shared/tree/master/C-ObjC-Swift/Performance_Console

In particular, the example calls an Objective-C and a C++ function from the Swift . 特别是，该示例从Swift调用了Objective-C和C ++函数 。

The key is to create a shared header, Project-Bridging-Header.h, and put the Objective-C headers there. 关键是创建一个共享头Project-Bridging-Header.h，然后在其中放置Objective-C头。

Please download the project as a complete example. 请下载该项目作为完整示例。

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如何从Swift调用Objective-C代码？

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