在您看来,如果我使用这样的参数初始化NSObject的单例子类:
- (MyObject *) initWithSomeParam:(NSString *)param{
self = [super init];
if (SharedInstance == nil){
SharedInstance = [super init];
SharedInstance.someProperty = param;
}
return self;
}
+ (MyObject *) objectWithSomeParam:(NSString *)param{
return [[self alloc] initWithSomeParam:param];
// Will the alloc cause a leak?
}
用户无权访问实例方法,只能访问类。感谢。
答案 0 :(得分:3)
这不是实现单例的正常方式,而是打破了init
的约定。更好的方法是创建一个sharedInstance
类方法,让initWithParam
方法更加传统:
static MyObject *_sharedInstance = nil;
+ (MyObject *)sharedInstance:(NSString *)param
{
if (_sharedInstance == nil)
{
_sharedInstance = [MyObject alloc] initWithParam:param];
}
return _sharedInstance;
}
// This must be called during app termination to avoid memory leak
+ (void)cleanup
{
[_sharedInstance release];
_sharedInstance = nil;
}
- (id)initWithParam:(NSString *)param
{
self = [super init];
if (self != nil)
{
self.someProperty = param;
}
return self;
}
然而,即使这样看起来也不太舒服;即,如果用户使用不同的参数调用sharedInstance
会发生什么?也许您想保留NSMutableDictionary
初始化对象并根据参数创建/返回它们?
如果是这样,你会这样做:
static NSMutableDictionary _sharedInstances = [[NSMutableDictionary alloc] init];
+ (MyObject *)sharedInstance:(NSString *)param
{
MyObject *obj = [_sharedInstances objectForKey:param];
if (obj == nil)
{
obj = [[MyObject alloc] initWithParam:param];
[_sharedInstances setObject:obj forKey:param];
}
return obj;
}
// This must be called during app termination to avoid memory leak
+ (void)cleanup
{
[_sharedInstances release];
_sharedInstances = nil;
}