IOS開發-深.淺拷貝與copy.strong

深.淺拷貝

• copy/mutableCopy NSString

NSString *string = @"漢斯哈哈哈"; // 沒有產生新對象 NSString *copyString = [string copy]; // 產生新對象 NSMutableString *mutableCopyString = [string mutableCopy]; NSLog(@"string = %p copyString = %p mutableCopyString = %p", string, copyString, mutableCopyString);

• copy/mutableCopy NSMutableString

NSMutableString *string = [NSMutableString stringWithString:@"漢斯哈哈哈"]; // 產生新對象 NSString *copyString = [string copy]; // 產生新對象 NSMutableString *mutableCopyString = [string mutableCopy]; NSLog(@"string = %p copyString = %p mutableCopyString = %p", string, copyString, mutableCopyString);

結論：

注意：其餘對象NSArray、NSMutableArray 、NSDictionary、NSMutableDictionary同樣適用

• copy NSObject

HSPerson *p = [[HSPerson alloc] init]; p.age = 20; p.height = 170.0; HSPerson *copyP = [p copy]; // 這裏崩潰

崩潰：

看崩潰信息HSPerson應該先實現：

- (id)copyWithZone:(NSZone *)zone;

測試：

#import "HSPerson.h" @interface HSPerson()<NSCopying> @end @implementation HSPerson - (id)copyWithZone:(NSZone *)zone { return @"漢斯哈哈哈"; } @end

HSPerson *p = [[HSPerson alloc] init]; p.age = 20; p.height = 170.0; HSPerson *copyP = [p copy]; NSLog(@"copyP: %@", copyP);

能夠看出copyWithZone從新分配新的內存空間，則：

- (id)copyWithZone:(NSZone *)zone
{
    HSPerson *person = [[HSPerson allocWithZone:zone] init]; return person; // 有些人可能下面alloc,從新初始化空間，但這方法已給你分配了zone，本身就無需再次alloc內存空間了 // HSPerson *person = [[HSPerson alloc] init]; }

HSPerson *p = [[HSPerson alloc] init]; p.age = 20; p.height = 170.0; HSPerson *copyP = [p copy]; NSLog(@"p = %p copyP = %p", p, copyP); NSLog(@"age = %d height = %f", copyP.age, copyP.height);

雖然copy了份新的對象，然而age,height值並未copy，那麼：

- (id)copyWithZone:(NSZone *)zone
{
    HSPerson *person = [[HSPerson allocWithZone:zone] init]; person.age = self.age; person.height = self.height; // 這裏self其實就要被copy的那個對象，很顯然要本身賦值給新對象，因此這裏能夠控制copy的屬性 return person; }

這時你會想，有NSMutableCopying？沒錯，是有這貨：

- (id)mutableCopyWithZone:(NSZone *)zone
{
    HSPerson *person = [[HSPerson allocWithZone:zone] init]; person.age = self.age; person.height = self.height; return person; }

NSCopying、NSMutableCopying有啥區別？
其實感受不必有NSMutableCopying，由於壓根就沒可變的HSPerson，但若是該對象有其餘行爲，能夠借用NSMutableCopying實現，哈哈哈

property裏的copy、strong區別

說完深淺拷貝，理解property裏的copy、strong就輕鬆多了！

• copy

#import <Foundation/Foundation.h> @interface HSPerson : NSObject @property (nonatomic, copy) NSString *name; @end

NSMutableString *string = [NSMutableString stringWithFormat:@"漢斯哈哈哈"]; HSPerson *person = [[HSPerson alloc] init]; person.name = string; // 不能改變person.name的值，由於其內部copy新的對象 [string appendString:@" hans"]; NSLog(@"name = %@", person.name);

property copy 實際上就對name幹了這個：

- (void)setName:(NSString *)name { _name = [name copy]; }

假設name爲NSMutableString，會發生什麼事？

@property (nonatomic, copy) NSMutableString *name;

這樣會捱罵哦，實際上內部仍是：

- (void)setName:(NSMutableString *)name { _name = [name copy]; }

copy出來的仍然是不可變字符！若是有人用NSMutableString的方法，就會崩潰:

• strong

@property (nonatomic, strong) NSString *name;

NSMutableString *string = [NSMutableString stringWithFormat:@"漢斯哈哈哈"]; HSPerson *person = [[HSPerson alloc] init]; person.name = string; // 能夠改變person.name的值，由於其內部沒有生成新的對象 [string appendString:@" hans"]; NSLog(@"name = %@", person.name);