什么时候设置 Objective-C 属性双保留？
给出以下代码
@interface MyClass
{
SomeObject* o;
}
@property (nonatomic, retain) SomeObject* o;
@implementation MyClass
@synthesize o;
- (id)initWithSomeObject:(SomeObject*)s
{
if (self = [super init])
{
o = [s retain]; // WHAT DOES THIS DO? Double retain??
}
return self
}
@end
Given the following code
@interface MyClass
{
SomeObject* o;
}
@property (nonatomic, retain) SomeObject* o;
@implementation MyClass
@synthesize o;
- (id)initWithSomeObject:(SomeObject*)s
{
if (self = [super init])
{
o = [s retain]; // WHAT DOES THIS DO? Double retain??
}
return self
}
@end
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评论（1）
它不是双重保留；
s只会保留一次。原因是您没有在初始化程序中调用合成的 setter 方法。此行：
保留
s并将o设置为等于s；也就是说，o和s指向同一个对象。合成的访问器永远不会被调用；您可以完全摆脱@property和@synthesize行。如果该行是：
或等效的
，则将调用合成访问器，这将再次保留该值。请注意，通常不建议在初始化程序中使用访问器，因此在编写
init函数时，o = [s keep];是更常见的用法。It is not a double retain;
swill only be retained once.The reason is that you're not invoking the synthesized setter method within your initializer. This line:
retains
sand setsoto be equal tos; that is,oandspoint to the same object. The synthesized accessor is never invoked; you could get rid of the@propertyand@synthesizelines completely.If that line were:
or equivalently
then the synthesized accessor would be invoked, which would retain the value a second time. Note that it generally not recommended to use accessors within initializers, so
o = [s retain];is the more common usage when coding aninitfunction.