iOS開發中，物件的拷貝有兩種方法，就是江湖中流傳的『淺拷貝』與『深拷貝』。淺拷貝意即不拷貝內容的本身，只對其指標進行復制，而深拷貝就是對內容的拷貝了，即是把內容拷貝到一塊新的記憶體中去。apple iOS官方文件中有個圖，一看就明白是咋回事了，如下圖
1、集合的深淺拷貝
NSArray *contentArray = @[@"鼠",@"牛",@"虎",@"兔",@"龍",@"蛇",@"馬"];
NSSet *contentSet = [[NSSet alloc] initWithObjects:@"羊",@"猴",@"雞",@"狗",@"豬", nil];
NSDictionary *contentDic = @{@"shu" : @"鼠",
@"niu" : @"牛",
@"hu" : @"虎",
@"tu" : @"兔",
@"long" : @"龍"};
/* 淺複製 */
NSArray *shallowCopyArray = [contentArray copyWithZone:nil];
NSArray *shallowCopyArray2 = [[NSArray alloc] initWithArray:contentArray copyItems:NO];
NSSet *shallowCopySet = [contentSet copyWithZone:nil];
NSSet *shallowCopySet2 = [[NSSet alloc] initWithSet:contentSet copyItems:NO];
NSDictionary *shallowCopyDic = [contentDic copyWithZone:nil];
NSDictionary *shallowCopyDic2 = [[NSDictionary alloc] initWithDictionary:contentDic copyItems:NO];
/* 深複製 */
NSArray *deepCopyArray = [[NSArray alloc] initWithArray:contentArray copyItems:YES];
NSSet *deepCopySet = [[NSSet alloc] initWithSet:contentSet copyItems:YES];
NSDictionary *deepCopyDic = [[NSDictionary alloc] initWithDictionary:contentDic copyItems:YES];
//一組資料可觀察出深淺拷貝
NSLog(@"contentArray is %p,pointer is %p",contentArray,&contentArray);
NSLog(@"shallowCopyArray is %p,pointer is %p",shallowCopyArray,&shallowCopyArray);
NSLog(@"shallowCopyArray2 is %p,pointer is %p",shallowCopyArray2,&shallowCopyArray2);
NSLog(@"deepCopyArray is %p,pointer is %p",deepCopyArray,&deepCopyArray);
/*列印
contentArray is 0x604000289b00,pointer is 0x7ffee0d8c7c8
shallowCopyArray is 0x604000289b00,pointer is 0x7ffee0d8c7b0
shallowCopyArray2 is 0x604000289b00,pointer is 0x7ffee0d8c7a8
deepCopyArray is 0x60400028a000,pointer is 0x7ffee0d8c780
*/
複製程式碼由列印的結果，可以證明淺拷貝與深拷貝的區別了。
2、集合/非集合型別的copy與mutableCopy
除了上面的方法，拷貝物件時還可使用copy、mutableCopy，具體使用如下：
NSArray *imutableArray = @[@"a",@"b",@"c"];
NSArray *mutableArray = [NSMutableArray arrayWithObjects:@"d",@"e",@"f",nil];
NSString *imutableString = @"imutableString";
NSMutableString *mutableString = [NSMutableString stringWithString:imutableString];
//
//imutable物件 copy與mutableCopy
NSArray *imutable_copyArray = [imutableArray copy];
NSMutableArray *imutable_mutableCopyArray = [imutableArray mutableCopy];
//[imutable_mutableCopyArray addObject:@"something2"];
NSLog(@"———————————————————————————集合型別的copy star——————————————————————————————");
NSLog(@"imutableArray is %p,pointer is %p",imutableArray,&imutableArray);
NSLog(@"imutable_copyArray is %p,pointer is %p",imutable_copyArray,&imutable_copyArray);
NSLog(@"imutable_mutableCopyArray is %p,pointer is %p",imutable_mutableCopyArray,&imutable_mutableCopyArray);
NSLog(@"———————————————————————————end——————————————————————————————");
//
NSString *imutable_copyString = [imutableString copy];
NSMutableString *imutable_mutableCopyString = [imutableString mutableCopy];
[imutable_mutableCopyString appendString:@"someString2"];
NSLog(@"———————————————————————————非集合型別的copy star——————————————————————————————");
NSLog(@"imutableString is %p,pointer is %p",imutableString,&imutableString);
NSLog(@"imutable_copyString is %p,pointer is %p",imutable_copyString,&imutable_copyString);
NSLog(@"imutable_mutableCopyString is %p,pointer is %p",imutable_mutableCopyString,&imutable_mutableCopyString);
NSLog(@"———————————————————————————end——————————————————————————————");
//mutable物件 copy與mutableCopy
NSMutableArray *mutable_copyArray = [mutableArray copy];
// [mutable_copyArray addObject:@"otherthing"];//runtime crash
NSMutableArray *mutable_mutableCopyArray = [mutableArray mutableCopy];
//[mutable_mutableCopyArray addObject:@"otherthing2"];
NSLog(@"———————————————————————————集合型別的mutableCopy star——————————————————————————————");
NSLog(@"mutableArray is %p,pointer is %p",mutableArray,&mutableArray);
NSLog(@"mutable_copyArray is %p,pointer is %p",mutable_copyArray,&mutable_copyArray);
NSLog(@"mutable_mutableCopyArray is %p,pointer is %p",mutable_mutableCopyArray,&mutable_mutableCopyArray);
NSLog(@"———————————————————————————end——————————————————————————————");
//
NSMutableString *mutable_copyString = [mutableString copy];
//[mutable_copyString appendString:@"otherString"];//runtime crash
NSMutableString *mutable_mutableCopyString = [mutableString mutableCopy];
[mutable_mutableCopyString appendString:@"otherString2"];
NSLog(@"———————————————————————————非集合型別的mutableCopy star——————————————————————————————");
NSLog(@"mutableString is %p,pointer is %p",mutableString,&mutableString);
NSLog(@"mutable_copyString is %p,pointer is %p",mutable_copyString,&mutable_copyString);
NSLog(@"mutable_mutableCopyString is %p,pointer is %p",mutable_mutableCopyString,&mutable_mutableCopyString);
NSLog(@"———————————————————————————end——————————————————————————————");
複製程式碼上面程式碼中有2個runtime crash,分別是
NSMutableArray *mutable_copyArray = [mutableArray copy];
// [mutable_copyArray addObject:@"otherthing"];//runtime crash
以及
NSMutableString *mutable_copyString = [mutableString copy];
//[mutable_copyString appendString:@"otherString"];//runtime crash
複製程式碼這裡要注意的一個點是，物件在使用copy方法之後，返回來的物件型別是不可變型別的（imutable），儘管你用一個可變型別的物件去接收，然後使用可變型別物件的方法，在執行時會crash，這是因為它終究是一個不可變（imutable）物件，由此可以得出第一個結論：
- 不管集合、非集合型別物件使用copy返回來的為不可變型別物件，如果對copy返回物件使用mutable物件的介面就會產生runtime crash，而物件使用mutableCopy返回來的則是不可變型別物件。
好，註冊crash程式碼後，再看看這段程式碼的最終列印結果：
- 對於不可變物件（imutable）使用copy為拷貝指標即淺拷貝，使用mutableCopy為內容拷貝；對於可變物件（mutable）使用copy、mutableCopy都為內容拷貝。
3、集合的深拷貝要注意的地方
先看一段程式碼，及其執行的結果：
NSLog(@"———————————————————————————imutable集合型別mutableCopy——————————————————————————————");
NSLog(@"imutableArray pointer:");
for (NSString *obj in imutableArray) {
NSLog(@"obj is %p,pointer is %p",obj,&obj);
}
NSLog(@"imutable_mutableCopyArray pointer:");
for (NSString *obj in imutable_mutableCopyArray) {
NSLog(@"obj is %p,pointer is %p",obj,&obj);
}
NSLog(@"———————————————————————————mutable集合型別copy與mutableCopy——————————————————————————————");
NSLog(@"mutableArray pointer:");
for (NSString *obj in mutableArray) {
NSLog(@"obj is %p,pointer is %p",obj,&obj);
}
NSLog(@"mutable_copyArray pointer:");
for (NSString *obj in mutable_copyArray) {
NSLog(@"obj is %p,pointer is %p",obj,&obj);
}
NSLog(@"mutable_mutableCopyArray pointer:");
for (NSString *obj in mutable_mutableCopyArray) {
NSLog(@"obj is %p,pointer is %p",obj,&obj);
}
複製程式碼列印出來的結果：
so，第三個結論：
- 對於可變集合（mutable集合）使用copy/mutableCopy雖說是內容拷貝，但只止於物件，集合元素還是指標拷貝，所以這是單層的深拷貝，並不是完全拷貝。