Objective-C和Swift的转换速查手册(推荐)
前言
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-C NSInteger score = 556; // NSString *name = @"Taylor"; // BOOL loggedIn = NO;
//Swift var score = 556 // var name = "Taylor" // var loggedIn = false
创建一个常量
//Objective-C const NSInteger score = 556; // NSString * const name = @"Taylor"; // const BOOL firstRun = YES; //Objective-C中常量用的很少
//Swift let 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-C NSArray *grades = @[@90, @85, @97]; // NSArray *names = @[@"Taylor", @"Adele", @"Justin"];
//Swift let grades = [90, 85, 97] // let names = ["Taylor", "Adele", "Justin"]
向数组中添加一个值类型
//Objective-C NSMutableArray *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
//Swift var array = [CGRect]() // array.append(CGRect(x: 0, y: 0, width: 32, height: 64))
创建一个字典
//Objective-C NSDictionary *houseNumbers = @{ @"Paul": @7, @"Jess": @56, @"Peter": @332 };
//Swift let houseNumbers = ["Paul": 7, "Jess": 56, "Peter": 332]
定义一个枚举
//Objective-C typedef NS_ENUM(NSInteger, ShapeType) { kCircle, kRectangle, kHexagon };
//Swift enum ShapeType: Int { case circle case rectangle case hexagon }
附加一串字符
//Objective-C NSString *first = @"Hello, "; NSString *second = [first stringByAppendingString:@" world!"];
//Swift let first = "Hello, " let second = first + "world!"
增加数字
//Objective-C NSInteger rating = 4; rating++; rating += 3;
//Swift var rating = 4 rating += 1 rating += 3
插入字符串
//Objective-C NSString *account = @"twostraws"; NSString *str = [NSString stringWithFormat:@"Follow me on Twitter: %@", account];
//Swift let account = "twostraws" let str = "Follow me on Twitter: \(account)"
打印调试信息
//Objective-C NSString *username = @"twostraws"; NSLog(@"Username is %@", username);
//Swift let username = "twostraws" print("Username is \(username)")
控制流
检查状态
//Objective-C NSInteger result = 86; if (result >= 85) { NSLog(@"You passed the test!"); } else { NSLog(@"Please try again."); }
//Swift let result = 86 if result >= 85 { print("You passed the test!") } else { print("Please try again.") }
循环一定次数
//Objective-C for (NSInteger i = 0; i < 100; ++i) { NSLog(@"This will be printed 100 times."); }
//Swift for _ in 0 ..< 100 { print("This will be printed 100 times.") }
在数组中循环
//Objective-C NSArray *companies = @[@"Apple", @"Facebook", @"Twitter"]; for (NSString *name in companies) { NSLog(@"%@ is a well-known tech company.", name); }
//Swift let companies = ["Apple", "Facebook", "Twitter"] for name in companies { print("\(name) is a well-known tech company.") }
数值切换
//Objective-C NSInteger 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
//Swift let rating = 8 switch 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];
//Swift func 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];
//Swift func 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
//Swift func printGreeting(for user: String) -> String { return "Hello, \(user)!" } let result = printGreeting(for: "Paul")
接收一个字符串和一个整数,返回一个字符串的函数
//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];
//Swift func 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
//Swift func 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-C void (^printUniversalGreeting)(void) = ^{ NSLog(@"Bah-weep-graaaaagnah wheep nini bong"); }; printUniversalGreeting();
//Swift let 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-C NSString* (^getUniversalGreeting)(void) = ^{ return @"Bah-weep-graaaaagnah wheep nini bong"; }; NSString *greeting = getUniversalGreeting(); NSLog(@"%@", greeting);
//Swift let 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-C NSString* (^getGreeting)(NSString *) = ^(NSString *name) { return [NSString stringWithFormat:@"Live long and prosper, %@.", name]; }; NSString *greeting = getGreeting(@"Paul"); NSLog(@"%@", greeting);
//Swift let 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
//Swift class 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
//Swift class 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
//Swift class 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
//Swift class 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-
//Swift class 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
//Swift extension String { func trimmed() -> String { return trimmingCharacters(in: .whitespacesAndNewlines) } }
检查一个对象的类
//Objective-C if ([object isKindOfClass:[YourClass class]]) { NSLog(@"This is a YourClass."); }
//Swift if object is YourClass { print("This is a YourClass.") }
类型转换
//Objective-C Dog *poodle = (Dog*)animalObject;
//Swift let 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-C dispatch_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"); }); });
//Swift DispatchQueue.global().async { print("Running in the background...") DispatchQueue.main.async { print("Running on the main thread") } }
总结
以上就是这篇文章的全部内容了,希望本文的内容对大家的学习或者工作具有一定的参考学习价值,如果有疑问大家可以留言交流,谢谢大家对我们的支持。
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