ios 正确覆盖 Objective-C 中的 setter
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原文地址: http://stackoverflow.com/questions/12369787/
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Correctly override setter in Objective-C
提问by E. Lüders
I just tried to override the standard synthesised setters of a property. So far everything is fine I just set the ivar to my new value. But then I asked myself 'what happens with the retain count of retained properties'... I found no good answer that explained this to me. So I ask it here. Is there anything I have to be aware of if I override a properties setter that is set to retainand how can I do it correctly? I do not use ARC.
我只是试图覆盖一个属性的标准合成设置器。到目前为止一切都很好，我只是将 ivar 设置为我的新值。但是后来我问自己“保留属性的保留计数会发生什么”......我没有找到可以向我解释这一点的好的答案。所以我在这里问。如果我覆盖设置为的属性设置器，我有什么需要注意的，我该retain如何正确地做到这一点？我不使用ARC。
Here's an example:
下面是一个例子：
@property(nonatomic)NSInteger number;
- (void)setNumber:(NSInteger)number {
_number = number; // This should be fine, since it's no retained object I want to set
}
@property(nonatomic, retain)NSObject *something;
- (void)setSomething:(NSObject *)something {
_something = something; // This is not fine. As far as I know you should never do sth. like this... But how do I set it correctly?
}
回答by Hot Licks
-(void) setAnObject:(NSObject*) someObject {
if (_anObject != someObject) {
NSObject* savedObject = _anObject;
_anObject = [someObject retain];
[savedObject release];
}
}
If you release the old pointer before retaining the new, you can have a situation where you're setting the value from a value in the old object, and the release of the old object causes the new object to go POOF! just before it's retained.
如果在保留新指针之前释放旧指针，则可能会出现从旧对象中的值设置值的情况，而旧对象的释放会导致新对象变成 POOF！就在它被保留之前。
Alternatively, you could do
或者，你可以做
....
[someObject retain];
[_anObject release];
_anObject = someObject;
...
回答by Thomas Johannesmeyer
Are you overwriting the setters just to have a different name? If that's the case you can do so by changing the property definition:
您是否只是为了使用不同的名称而覆盖设置器？如果是这种情况，您可以通过更改属性定义来实现：
@property(nonatomic, setter = nameOfSetter: )NSInteger number;
Same works for getter.
吸气剂也一样。
回答by Damo
Edited after studying accepted answer from Hot Licks
在研究了 Hot Licks 接受的答案后进行了编辑
property declaration and synthesis of x
x 的属性声明和合成
@property (nonatomic, retain) ClassX x;
@synthesize x = _x;
over-ridden setter for x
x 的重载 setter
- (void)setX:(ClassX *)x;
{
if (x != _x)
{
[x retain];
[_x release];
_x = x;
// custom code here
}
}
回答by Amy Worrall
- (void) setSomething:(NSObject*) something
{
if (something != _something)
{
[_something release];
_something = [something retain];
}
}
You need the ifstatement because otherwise, if something and _something were alreadythe same, you'd overrelease the object, have it possibly disappear, and have problems.
您需要该if语句，否则，如果 something 和 _something已经相同，则您会过度释放该对象，使其可能消失并出现问题。
