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江苏快3软件下载:Objective-C与Swift的转换速查手册 [复制链接]

2018-6-20 10:31
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江苏十一选五app下载 www.qt2od.cn 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

01.png

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)


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")
   }
}

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所有评论(1)
lwei667 2018-6-25 15:39
这个还是不错的
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