Objective-C与Swift的转换速查手册

如果你正要从Objective-C过渡到Swift，或反过来，一个在两种语言间显示等效代码的小手册会很有帮助。本文内容就是这些：苹果开发者的红宝书，包含变量，集合，函数，类等等。

下面例子中，上面是Objective-C代码，下面是等效的Swift代码。必要的地方我会给一些备注来帮助你理解。

变量与常量

创建一个变量

//Objective-CNSInteger score = 556;//NSString *name = @"Taylor";//BOOL loggedIn = NO;

//Swiftvar score = 556//var name = "Taylor"//var loggedIn = false

创建一个常量

//Objective-Cconst NSInteger score = 556;//NSString * const name = @"Taylor";//const BOOL firstRun = YES;//Objective-C中常量用的很少

//Swiftlet score = 556//let name = "Taylor"//let firstRun = true//Swift中常量很常见

创建一个变量数组

创建一个常量数组

//Objective-CNSArray *grades = @[@90, @85, @97];//NSArray *names = @[@"Taylor", @"Adele", @"Justin"];

//Swiftlet grades = [90, 85, 97]//let names = ["Taylor", "Adele", "Justin"]

向数组中添加一个值类型

//Objective-CNSMutableArray *array = [NSMutableArray new];//[array addObject:[NSValue valueWithRect:CGRectMake(0, 0, 32, 64)]];//在添加到集合前，值类型有对应的引用类型

//Swiftvar array = [CGRect]()//array.append(CGRect(x: 0, y: 0, width: 32, height: 64))

创建一个字典

//Objective-CNSDictionary *houseNumbers = @{ @"Paul": @7, @"Jess": @56, @"Peter": @332 };

//Swiftlet houseNumbers = ["Paul": 7, "Jess": 56, "Peter": 332]

定义一个枚举

//Objective-Ctypedef NS_ENUM(NSInteger, ShapeType) { kCircle, kRectangle, kHexagon};

//Swiftenum ShapeType: Int { case circle case rectangle case hexagon}

附加一串字符

//Objective-CNSString *first = @"Hello, ";NSString *second = [first stringByAppendingString:@" world!"];

//Swiftlet first = "Hello, "let second = first + "world!"

增加数字

//Objective-CNSInteger rating = 4;rating++;rating += 3;

//Swiftvar rating = 4rating += 1rating += 3

插入字符串

//Objective-CNSString *account = @"twostraws";NSString *str = [NSString stringWithFormat:@"Follow me on Twitter: %@", account];

//Swiftlet account = "twostraws"let str = "Follow me on Twitter: \(account)"

打印调试信息

//Objective-CNSString *username = @"twostraws";NSLog(@"Username is %@", username);

//Swiftlet username = "twostraws"print("Username is \(username)")

控制流

检查状态

//Objective-CNSInteger result = 86;if (result >= 85) { NSLog(@"You passed the test!");} else { NSLog(@"Please try again.");}

//Swiftlet result = 86if result >= 85 { print("You passed the test!")} else { print("Please try again.")}

循环一定次数

//Objective-Cfor (NSInteger i = 0; i < 100; ++i) { NSLog(@"This will be printed 100 times.");}

//Swiftfor _ in 0 ..< 100 { print("This will be printed 100 times.")}

在数组中循环

//Objective-CNSArray *companies = @[@"Apple", @"Facebook", @"Twitter"];for (NSString *name in companies) { NSLog(@"%@ is a well-known tech company.", name);} 

//Swiftlet companies = ["Apple", "Facebook", "Twitter"]for name in companies { print("\(name) is a well-known tech company.")}

数值切换

//Objective-CNSInteger rating = 8;switch (rating) { case 0 ... 3: NSLog(@"Awful"); break; case 4 ... 7: NSLog(@"OK"); break; case 8 ... 10: NSLog(@"Good"); break; default: NSLog(@"Invalid rating.");}//很多人不知道Objective-C有范围支持，所以你也许看到二选一的语法

//Swiftlet rating = 8switch rating {case 0...3: print("Awful")case 4...7: print("OK")case 8...10: print("Good")default: print("Invalid rating.")}//Swift不会fall through案例，除非你使用fallthrough关键字

函数

不接收参数也没有返回的函数

//Objective-C- (void)printGreeting { NSLog(@"Hello!");}[self printGreeting];

//Swiftfunc printGreeting() { print("Hello!")}printGreeting()

不接收参数，返回一个字符串的函数

//Objective-C- (NSString*)printGreeting { return @"Hello!";}NSString *result = [self printGreeting];

//Swiftfunc printGreeting() -> String { return "Hello!"}let result = printGreeting()

接收一个字符串，返回一个字符串的函数

//Objective-C- (NSString*)printGreetingFor:(NSString*)user { return [NSString stringWithFormat:@"Hello, %@!", user];}NSString *result = [self printGreetingFor:@"Paul"];//第一个参数的名称需要为方法名的一部分

//Swiftfunc printGreeting(for user: String) -> String { return "Hello, \(user)!"}let result = printGreeting(for: "Paul")

//Objective-C- (NSString*)printGreetingFor:(NSString*)user withAge:(NSInteger)age { if (age >= 18) { return [NSString stringWithFormat:@"Hello, %@! You're an adult.", user]; } else { return [NSString stringWithFormat:@"Hello, %@! You're a child.", user]; }}NSString *result = [self printGreetingFor:@"Paul" withAge:38];

//Swiftfunc printGreeting(for user: String, age: Int) -> String { if age >= 18 { return "Hello, \(user) You're an adult." } else { return "Hello, \(user)! You're a child." }}let result = printGreeting(for: "Paul", age: 38)

从函数返回多个值

//Objective-C- (NSDictionary*)loadAddress { return @{ @"house": @"65, Park Street", @"city": @"Bristol", @"country": @"UK" };}NSDictionary*address = [self loadAddress];NSString *house = address[@"house"];NSString *city = address[@"city"];NSString *country = address[@"country"];//Objective-C不支持元祖(tuple),所以用字典或数组替代

//Swiftfunc loadAddress() -> (house: String, city: String, country: String) { return ("65, Park Street", "Bristol", "UK")}let (city, street, country) = loadAddress()

不接收参数没有返回的闭环

//Objective-Cvoid (^printUniversalGreeting)(void) = ^{ NSLog(@"Bah-weep-graaaaagnah wheep nini bong");};printUniversalGreeting();

//Swiftlet universalGreeting = { print("Bah-weep-graaaaagnah wheep nini bong")}universalGreeting()

不接收参数返回一个字符串的闭环

//Objective-CNSString* (^getUniversalGreeting)(void) = ^{ return @"Bah-weep-graaaaagnah wheep nini bong";};NSString *greeting = getUniversalGreeting();NSLog(@"%@", greeting);

//Swiftlet getUniversalGreeting = { return "Bah-weep-graaaaagnah wheep nini bong"}let greeting = getUniversalGreeting()print(greeting)

接收一个字符串参数，返回一个字符串的闭环

//Objective-CNSString* (^getGreeting)(NSString *) = ^(NSString *name) { return [NSString stringWithFormat:@"Live long and prosper, %@.", name];};NSString *greeting = getGreeting(@"Paul");NSLog(@"%@", greeting);

//Swiftlet getGreeting = { (name: String) in return "Live long and prosper, \(name)."}let greeting = getGreeting("Paul")print(greeting)

类

创建空类

//Objective-C@interface MyClass : NSObject@end@implementation MyClass@end

//Swiftclass MyClass: NSObject {}//推荐使用结构代替类，这样也许不需要从NSObject继承了

创建有2个属性的类

//Objective-C@interface User : NSObject@property (nonatomic, copy) NSString *name;@property (nonatomic, assign) NSInteger age;@end@implementation User@end

//Swiftclass User { var name: String var age: Int  init(name: String, age: Int) { self.name = name self.age = age }}//Swift要求进行初始化，给这些属性默认值

创建有一个私有属性的类

//Objective-C//在头文件中@interface User : NSObject@property (nonatomic, copy) NSString *name;@end//在执行文件中@interface User()@property (nonatomic, assign) NSInteger age;@end@implementation User@end//Objective-C实际上并不支持私有属性，通常都用这种变通方式

//Swiftclass User { var name: String private var age: Int  init(name: String, age: Int) { self.name = name self.age = age }}

创建有一个实例方法的类

//Objective-C@interface Civilization : NSObject- (NSInteger)getMeaningOfLife;@end@implementation Civilization- (NSInteger)getMeaningOfLife { return 42;}@end

//Swiftclass Civilization { func getMeaningOfLife() -> Int { return 42 }}

创建有一个静态方法的类

//Objective-C@interface Civilization : NSObject+ (NSInteger)getMeaningOfLife;@end@implementation Civilization+ (NSInteger)getMeaningOfLife { return 42;}@end//差别很小，用+而不是- 

//Swiftclass Civilization { class func getMeaningOfLife() -> Int { return 42 }}//Swift也支持静态方法——它不会在子类中被覆盖

用一种新方法扩展一个类型

//Objective-C@interface NSString (Trimming)- (NSString*)trimmed;@end@implementation NSString (Trimming)- (NSString*)trimmed { return [self stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet]];}@end

//Swiftextension String { func trimmed() -> String { return trimmingCharacters(in: .whitespacesAndNewlines) }}

检查一个对象的类

//Objective-Cif ([object isKindOfClass:[YourClass class]]) { NSLog(@"This is a YourClass.");}

//Swiftif object is YourClass { print("This is a YourClass.")}

类型转换

//Objective-CDog *poodle = (Dog*)animalObject;

//Swiftlet poodle = animalObject as? Dog//let poodle = animalObject as! Dog//如果不是一个dog，前者会把poodle设为nil，后者则会崩溃

GCD

在不同线程运行代码

//Objective-Cdispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{ NSLog(@"Running in the background...");  dispatch_async(dispatch_get_main_queue(), ^{ NSLog(@"Running back on the main thread"); });});

//SwiftDispatchQueue.global().async { print("Running in the background...")  DispatchQueue.main.async { print("Running on the main thread") }}

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關鍵字: Objective-C 等效 Swift语言