[英]C++ object as an Objective-C++ property
I want to declare a C++ property inside my Objective-C class. 我想在Objective-C类中声明一个C ++属性。
What kind of attributes should I set it to? 我应该将它设置为什么类型的属性? It seems that strong
or retain
will lead to an error saying that it is not an object. 似乎strong
或retain
会导致错误,说它不是一个对象。
How could I manage its memory properly? 我怎样才能正确管理它的内存?
You are right, the property cannot be weak
, strong
, or retained
; 你是对的,财产不能weak
, strong
,或retained
; for that it would have to be a pointer to an Objective-C object. 因为它必须是指向Objective-C对象的指针。 If you don't use any attributes on a C++ property, it will default to unsafe_unretained,assign,atomic
. 如果不在C ++属性上使用任何属性,则默认为unsafe_unretained,assign,atomic
。
A few other things to consider, assuming the Objective-C(++) object controls the lifetime of the C++ property: 假设Objective-C(++)对象控制C ++属性的生命周期,还需要考虑其他一些事项:
atomic
, you need to use synchronization in the setter and need a custom getter, too. 因为属性默认为atomic
,所以您需要在setter中使用同步并且还需要自定义getter。 You could declare it nonatomic
, in which case you would not need to synchronize and would not need a custom getter. 你可以声明它nonatomic
,在这种情况下你不需要同步,也不需要自定义的getter。 dealloc
to ensure the C++ object is freed when the Objective-C++ object goes away. 您可以实现dealloc
以确保在Objective-C ++对象消失时释放C ++对象。 Here's some useful documentation from Apple: https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/ProgrammingWithObjectiveC/EncapsulatingData/EncapsulatingData.html . 以下是Apple的一些有用文档: https : //developer.apple.com/library/archive/documentation/Cocoa/Conceptual/ProgrammingWithObjectiveC/EncapsulatingData/EncapsulatingData.html 。
And here is a quick example. 这是一个简单的例子。 Let's say the C++ class you are using for the property is called MyCPP
. 假设您为该属性使用的C ++类称为MyCPP
。 In a header you could have: 在标题中你可以:
@interface ClassOCPP : NSObject
// This property can only be used in Objective-C++ code
#ifdef __cplusplus
@property /*(unsafe_unretained,assign,atomic)*/ MyCPP * myCPP;
#endif
// Other stuff may be usable in regular Objective-C code.
@end
Implementation could be as follows (in a .mm
file; remember, it's Objective-C++): 实现可以如下(在.mm
文件中;记住,它是Objective-C ++):
@implementation ClassOCPP
{
MyCPP * _myCPP;
}
-(id)init {
self = [super init];
_myCPP = NULL;
return self;
}
-(void)setMyCPP:(MyCPP*)newVal {
@synchronized(self) {
delete _myCPP; // it's OK to delete a NULL pointer
_myCPP = newVal;
}
}
-(MyCPP*)myCPP {
return _myCPP;
}
-(void)dealloc {
puts("De-allocating ClassOCPP.");
delete _myCPP;
}
@end
IIRC,你需要像任何其他C ++对象一样管理它,所以只需使用assign
作为属性,你应该很好。
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