addObjectsFromArray 与 mutableCopy
我有以下代码：
self.itemsCopy = [self.items mutableCopy];
//[self.itemsCopy addObjectsFromArray:self.items];
NSLog(@"------- BEFORE APPEND --------");
NSLog(@"items count: %d",[items count]);
NSLog(@"itemsCopy count: %d",[itemsCopy count]);
我的结果是：
------- BEFORE APPEND --------
items count: 15
itemsCopy count: 15
但是，如果我将第一行从 mutableCopy 更改为 addObjectsFromArray：
[self.itemsCopy addObjectsFromArray:self.items];
我的新结果是：
------- BEFORE APPEND --------
items count: 15
itemsCopy count: 0
为什么 mutableCopy 填充 itemsCopy，但 addObjectsFromArray 不填充？
I have the following code:
self.itemsCopy = [self.items mutableCopy];
//[self.itemsCopy addObjectsFromArray:self.items];
NSLog(@"------- BEFORE APPEND --------");
NSLog(@"items count: %d",[items count]);
NSLog(@"itemsCopy count: %d",[itemsCopy count]);
My results are:
------- BEFORE APPEND --------
items count: 15
itemsCopy count: 15
However if I change the first line from a mutableCopy to addObjectsFromArray:
[self.itemsCopy addObjectsFromArray:self.items];
My new results are:
------- BEFORE APPEND --------
items count: 15
itemsCopy count: 0
Why does mutableCopy populate itemsCopy, but addObjectsFromArray doesn't?
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因为 self.itemsCopy 是 nil 因为你错过了用 NSMutableArray 初始化它。
Because self.itemsCopy is nil as you missed to initialize it with a NSMutableArray.