Objective-C 程序設計語言采用特定的語法，來定義類和方法、調用對象的方法、動態地擴展類，以及創建編程接口，來解決具體問題。Objective-C 作為 C 程序設計語言的超集，支持與 C 相同的基本語法。有C#語言的編程經驗，那么Objective-C將更容易上手，本文將從各個方面對比C#與Objective-C的語法。
字符串
聲明：
C#: string name = “lwme.cnblogs.com”; Objective-C: NSString *name = @”lwme.cnblogs.com”;
字符串前面的@符號是objc在標准C語言基礎上添加的特性，"SteveZ"前面有一個@符號表示字符串應該作為Cocoa的NSString來處理，是把C string轉換成NSString的一個簡寫。
獲取長度：
C#: name.Length Objective-C: [name length] name.length
轉換：
C#: int i = 10; string age = i.ToString(); int intAge = int.Parse(age); Objective-C: NSInteger i = 10; NSString *age = [@(i) stringValue]; // 轉換成NSNumber再獲取字符串值 NSString *age = [NSString stringWithFormat:@"%d", i]; NSInteger intAge = [age integerValue];
拼接：
C#: string host = "lwme" + ".cnblogs.com"; Objective-C: NSString *host = @"lwme" @".cnblogs.com" NSString *host = [@"lwme" stringByAppendingString:@".cnblogs.com"]; NSString *host = [NSString stringWithFormat:@"%@%@", @"lwme", @".cnblogs.com"];
比較：
C#: bool isEqual = strA == strB; bool isEqual = string.Compare(strA, strB, true) == 0; // 忽略大小寫 bool isEqual = string.Compare(strA, strB, StringComparison.InvariantCultureIgnoreCase) == 0; bool isStartWith = strA.StartsWith(strB); bool isStartWith = strA.StartsWith(strB, StringComparison.InvariantCultureIgnoreCase); bool isEndWith = strA.EndsWith(strB); bool isEndWith = strA.EndsWith(strB, StringComparison.InvariantCultureIgnoreCase); bool isContain = strA.Contains(strB); bool isContain = strA.Contains(strB, StringComparison.InvariantCultureIgnoreCase); Objective-C: BOOL isEqual = [strA isEqualToString: strB]; BOOL isEqual = [strA caseInsensitiveCompare:strB] == NSOrderedSame; // 忽略大小寫 BOOL isEqual = [strA compare:strB options:NSCaseInsensitiveSearch] == NSOrderedSame; BOOL isStartWith = [strA hasPrefix:strB]; BOOL isEndWith = [strA hasSuffix:strB]; BOOL isContain = [strA rangeOfString:strB].location != NSNotFound; BOOL isContain = [strA rangeOfString:strB options:NSCaseInsensitiveSearch].location != NSNotFound;
檢查是否為空：
C#: bool empty = string.IsNullOrEmpty(value); bool empty = string.IsNullOrWhiteSpace(value); Objective-C: BOOL empty = (value == nil || value.length == 0); BOOL empty = (value == nil || value.length == 0 || [[value stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]] length] == 0); // 同IsNullOrWhiteSpace
轉換大小寫：
C#: string name = value.ToLower(); string name = value.ToUpper(); Objective-C: NSString *name = [value lowercasestring]; NSString *name = [value uppercasestring];
格式化：
C#:
float x = 2.43534f;
string s = x.ToString(“n2″);
string s = string.Format("{0} {1}", "lwme", "cnblogs");
Objective-C:
float x = 2.34454f;
NSString *s = [NSString stringWithFormat: @"%.2f", x];
NSString *s = [NSString stringWithFormat: @"%@ %@", @"lwme", @"cnblogs"];
可變字符串
objc和C#一樣，字符串都是不可變的，要改變字符串則分別需要使用StringBuilder、NSMutableString。
C#:
StringBuilder builder = new StringBuilder(20);
builder.Append("lwme");
builder.AppendFormat(".{0}.{1}", "cnblogs", "com");
Objective-C:
NSMutableString *builder = [NSMutableString stringWithCapacity:20];
[builder appendString:@"lwme"];
[builder appendFormat:@".%@.%@", @"cnblogs", @"com"];
數組
聲明：
C#:
string[] data = {};
string[] data = {"one", "two"};
Objective-C:
// 舊語法
NSArray* data = [NSArray arrayWithObjects:@"one", @"two", nil]; // (定義數組時用逗號分隔對象列表，並且必須以nil結尾)
// objc 2.0新語法
NSArray *data = @[]; //空數組
NSArray* data = @[@"one", @"two"];
獲取長度：
C#: data.Length Objective-C: [data count] data.count
獲取/設置元素值：
C#: data[0] data[0]="two"; Objective-C: [data objectAtIndex:0] data[0] // objc 2.0 新語法 data[0]=@"two";
查找元素：
C#:
int index = data.IndexOf("one");
Objective-C:
int index = [data indexOfObject:@"one"];
遍歷：
C#: foreach (string item in array) ... Objective-C: for (NSString *item in array) ...
可變數組
objc和C#一樣，數組是不可變的，如果需要改變數組的元素，則分別要用到List<T>、NSMutableArray。
C#:
List<string> list = new List<string>();
List<string> list = new List<string>(20);
List<string> list = new List<string> { "lwme", "cnblogs" };
list.Add("lwme");
list.AddRange(new[] { "l", "w", "m", "e" });
list.Insert(0, "lwme");
list.Remove("lwme");
list.RemoveAt(0);
list.Clear();
bool isContain = list.Contains("lwme");
bool isContain = list.Contains("lwme", StringComparer.InvariantCultureIgnoreCase);
Objective-C:
NSMutableArray *list = [NSMutableArray array];
NSMutableArray *list = [NSMutableArray arrayWithCapcity: 20];
NSMutableArray *list = [@[@"lwme", @"cnblogs"] mutableCopy];
[list addObject:@"lwme"];
[list addObjectsFromArray:@[@"lwme, @"cnblogs"]];
[list insertObject:@"lwme", atIndex:0];
[list removeObject:@"lwme"];
[list removeObjectAtIndex:0];
[list removeAllObjects];
BOOL isContain = [list containsObject:@"lwme"];
字典
在objc中有不可變的字典NSDictionary，在C#中沒有對應的，而可變的字典NSMutableDictionary對應C#中的Dictionary<TKey,TValue>。
C#:
Dictionary<string, string> dict = new Dictionary<string, string>();
Dictionary<string, string> dict = new Dictionary<string, string>(20);
Dictionary<string, string> dict = new Dictionary<string, string> { {"name", "lwme"}, {"host", "cnblogs"} };
dict.Add("name", "lwme");
dict["name"] = "lwme";
dict.Remove("name");
dict.Clear();
dict.ContainsKey("name");
string name = dict["name"]; // dict.TryGetValue("name", out ...)
Objective-C:
NSDictionary *dict = [NSDictionary dictionaryWithObjectsAndKeys: @"lwme", @"name", @"cnblogs", @"host", nil]; // 舊語法
NSDictionary *dict = @{@"name": @"lwme", @"host": @"cnblogs"}; // objc2.0語法
NSMutableDictionary *dict = [NSMutableDictionary dictionary];
NSMutableDictionary *dict = [NSMutableDictionary dictionaryWithCapacity: 20];
NSMutableDictionary *dict = [@{@"name": @"lwme", @"host": @"cnblogs"} mutableCopy];
[dict setObject:@"lwme" forKey:@"name"];
[dict removeObjectForKey:@"name"];
[dict removeAllObjects];
BOOL isContain = [[dict allKeys] containsObject:@"name"];
BOOL isContain = [dict objectForKey:@"name"] != nil;
NSString *name = [dict objectForKey:@"name"];
NSString *name = dict[@"name"];
各種數值
objc中有c語言的基本類型如int、float、struct等，還有它們的封裝類型NSNumber，由於NSArray、NSDictionary只能存儲對象，不能存儲任何基本類型，所以這些基本類型需要用NSNumber來包裝。
C#: int ii = 1; long li = 1; float fi = 1.1; double di = 1.1; bool b = true; Objective-C: int ii = 1; long li = 1; float fi = 1.1; double di = 1.1; bool b = true; BOOL b = YES; NSNumber ii = [NSNumber numberWithInt: 1]; NSNumber li = [NSNumber numberWithLong: 1]; NSNumber fi = [NSNumber numberWithFloat: 1.1]; NSNumber di = [NSNumber numberWithDouble: 1.1]; NSNumber b = [NSNumber numberWithBOOL: YES]; NSNumber ii = @1; NSNumber li = @1; NSNumber fi = @1.1; NSNumber di = @1.1; NSNumber b = @YES;
類、屬性、方法
objc的類分成.h頭文件和.m實現文件，.h頭文件里定義所有公開的方法、屬性、字段，.m實現文件里實現公開的方法以及私有的字段、方法。
C#:
public class Person
{
private int privateField;
public int Age {get;set;}
public string FirstName {get;set;}
public string LastName {get;set;}
public Person(int age) {
this.Age = age;
this.OnAgeChange(age);
}
private void OnAgeChange(int age) {
}
public string GetFullName() {
return this.FirstName + " " + this.LastName;
}
public void SetFullName(string firstName, string lastName) {
this.FirstName = firstName;
this.LastName = lastName;
}
public virtual void PrintAge(){
Console.WriteLine("{0}", this.Age);
}
public static Person CreatePerson(int age) {
return new Person(age);
}
}
Objective-C:
Person.h：
@interface Person : NSObject
-(id)initWithAge:(int)age; // 構造器
@property(nonatomic) int age; // 屬性
@property(nonatomic) NSString *firstName;
@property(nonatomic) NSString *lastName;
-(NSString*)getFullName; // 方法
-(void)setFullName:(NSString *)firstName andLastName:(NSString *)lastName;
-(void)printAge;
+(id)createPersonWithAge:(int)age;
@end
Person.m：
@interface Person()
{
int _privateField; // 私有字段
}
@end
@implementation Person
@synthesize age, firstName, lastName;
-(id)initWithAge:(int)age
{
if(self = [super init])
{
self.age = age;
[self onAgeChange:age];
}
return self;
}
-(void)onAgeChange:(int)age
{
}
-(NSString*)getFullName
{
return [NSString stringWithFormat:"%@ %@", self.firstName, self.lastName];
}
-(void)setFullName:(NSString *)firstName andLastName:(NSString *)lastName
{
self.firstName = firstName;
self.lastName = lastName;
}
-(void)printAge
{
NSLog(@"%i", self.age);
}
+(id)createPersonWithAge:(int)age
{
return [[Person alloc] initWithAge:age];
}
@end
訪問對象屬性：
C#:
Person p = new Person(11);
Person p = Person.CreatePerson(11);
p.setFullName("lwme", "cnblogs");
p.FirstName = "lwme";
p.PrintAge();
string fullName = p.GetFullName();
int age = p.Age;
Objective-C:
Person *p = [[Person alloc] initWithAge:11];
Person *p = [Person CreateWithAge:11];
[p setFullName:@"lwme" andLastName:@"cnblogs"];
p.firstName = @"lwme";
[p PrintAge];
NSString *fullName = [p getFullName];
int age = p.Age;
繼承及調用父類方法：
C#:
public class ChildPerson: Person
{
public ChildPerson(int age): base(age){}
public override void PrintAge() {
base.PrintAge();
Console.WriteLine("print age in childperson");
}
}
Objective-C:
ChildPerson.h
@interface ChildPerson:Person
@end
ChildPerson.m
@interface ChildPerson()
@end
@implementation ChildPerson
-(void)printAge
{
[super printAge];
NSLog(@"print age in childperson");
}
@end
獲取描述信息：
C#: ChildPerson p = new ChildPerson(11); string val = p.ToString(); Objective-C: ChildPerson *p = [[ChildPerson alloc] initWithAge:11]; NSString *val = [p description];
接口及事件
objc中的協議可以對應C#中的接口、事件，其中事件一般聲明為delegate名稱的屬性，在使用的時候只需要設置delete就可以綁定所有事件。
聲明及實現：
C#
public interface IEquatable<T>
{
bool Equals(T obj);
}
public class Person : IEquatable<MyClass>
{
public Action<Person> onAgeChanged;
public int Age { get; set; }
public bool Equals(Person p)
{
return p.Age == this.Age;
}
public void SetAge(int age) {
this.Age = age;
if (onAgeChanged != null)
onAgeChanged(this);
}
}
Objective-C
@protocol IEquatable
@required
-(bool)equals: (Person*)obj;
@end
@protocol IChangeAction
@optional
-(void)onAgeChange: (Person*)obj;
@end
@interface Person : NSObject<IEquatable>
@property(nonatomic) int age;
@property(nonatomic, weak)id<IChangeAction> delegate;
-(void)setAge:(int)age;
@end
@implementation Person
@synthesize age;
-(bool)equals:(Person*)p
{
return p.age == self.age;
}
-(void)setAge:(int)age
{
self.age = age;
if ([self.delegate respondsToSelector:@selector(onAgeChange:)])
[self.delegate onAgeChange:self];
}
@end
枚舉
聲明：
C#
public enum Orientation: uint {
Vertical = 0,
Horizontal = 1
}
Objective-C
typedef enum Orientation : NSUInteger {
OrientationVertical = 0,
OrientationHorizontal = 1
} Orientation;
使用：
C#
public Orientation TextAlignment {get;set} // 屬性
label.TextAlignment = Orientation.Horizontal;
Objective-C
@property(nonatomic, assign) Orientation textAlignment;
label.textAlignment = OrientationHorizontal;
反射
獲取對象類型：
C#: Type t = typeof(Person); Objective-C: Class c = [Person class];
獲取實例類型：
C#: Person p = new Person(); Type t = p.GetType(); Objective-C: Person *p = [[Person alloc] init]; Class c = p.class;
獲取類型名稱：
C#: string name = type.Name; string name = typeof(Person).Name; Objective-C: NSString *name = NSStringFromClass(p.class); NSString *name = NSStringFromClass([Person class]);
判斷實例類型：
C#: bool isPerson = p is Person; Objective-C: BOOL isPerson = [p isKindOfClass:c];
判斷是否繼承：
C#: bool isInherited = p is Person; bool isInherited = p.GetType().IsSubclassOf(typeof(Person)); bool isInherited = typeof(ChildPerson).IsSubclassOf(typeof(Person)); bool isInherited = typeof(Person).IsAssignableFrom(typeof(ChildPerson)); Objective-C: BOOL isInherited = [[p class] isSubclassOfClass:[Person class]]; BOOL isInherited = [[ChildPerson class] isSubclassOfClass:[Person class]];
判斷是否實現接口/協議：
C#: bool isImplemented = p is IEquatable; bool isImplemented = typeof(IEquatable<>).IsAssignableFrom(p.GetType()); bool isImplemented = typeof(IEquatable<>).IsAssignableFrom(typeof(Person)); bool isImplemented = typeof(Person).GetInterfaces().Contains(typeof(IEquatable<>)); Objective-C: BOOL isImplemented = [p class conformsToProtocol:@protocol(IEquaatable)];
從類型名稱創建實例：
C#:
object instance = Activator.CreateInstance(Type.GetType("ChildPerson"));
Objective-C:
id instance = [[NSClassFromString("ChildPerson") alloc] init];
獲取、調用方法：
C#:
MethodInfo method = type.GetMethod("PrintAge");
bool hasMethod = method != null;
method.Invoke(p, null);
Objective-C:
SEL method = @selector(printAge);
BOOL hasMethod = [p respondsToSelector: method];
[p performSelector:method];
獲取屬性：
C#:
object age = p.GetType().GetProperty(“Age”).GetValue(p, null);
foreach(PropertyInfo pi in typeof(Person).GetProperties())
{
// pi.Name
}
Objective-C:
id age = [p valueForKey:@"Age"];
unsigned int propertyCount = 0;
objc_property_t * properties = class_copyPropertyList([Person class], &propertyCount);
for (unsigned int i = 0; i < propertyCount; ++i) {
objc_property_t property = properties[i];
const char * name = property_getName(property);
}
free(properties);
擴展方法
objc里的Category可以很好的實現C#中的擴展方法。
C#
public static class PersonExtension {
public static void PrintFullName(this Person p) {
Console.WriteLine(p.GetFullName());
}
}
Objective-C
Person+PrintExtension.h
#import "Person.h"
@interface Person (PrintExtension)
-(void)PrintFullName;
@end
Person+PrintExtension.m
@implementation Person (PrintExtension)
-(void)PrintFullName
{
NSLog(@"%@", [self getFullName]);
}
@end
異常處理
C#
try {
} catch (Exception ex) {
} finally {
}
Objective-C
@try {
}
@catch (NSException *exception) {
}
@finally {
}
命名空間
objc沒有命名空間機制，直接從包或者當前項目引入頭文件即可。
引用：
C# using System; using System.Text; using MyCompany.CustomNamespace; Objective-C #import <UIKit/UIKit.h> #import <Foundation/Foundation.h> #import "CustomClass.h"
內存管理
objc中有ARC機制對應.net 中的GC，詳細的可以看：http://snakcakeblog.tumblr.com/post/47765862590/grudge-match-c-gc-vs-objective-c-arc
程序集
在C#當中，源代碼一般被編譯成程序集，而在objc中，都是編譯成靜態鏈接庫，而且引用方式也不相同。
參考
http://www.infragistics.com/community/blogs/stevez/archive/2013/05/09/c-to-objective-c-the-ultimate-guide.aspx（本文內容主要來自它，並做了一些更改）
http://www.anotherchris.net/csharp/objective-c-by-example-for-a-csharp-developer/
http://www.cnblogs.com/chijianqiang/archive/2012/06/22/objc-category-protocol.html
http://www.techotopia.com/index.php/Working_with_String_Objects_in_Objective-C
http://overooped.com/post/41803252527/methods-of-concurrency