[iOS]定时器NSTimer、CADisplayLink的内存管理
NSTimer、CADisplayLink会对target产生强引用，如果target同时对他们产生强引用，则会发生循环引用。以NSTimer为例，解决循环引用的问题。
方法1：使用block
- (void)viewDidLoad {
;
// Do any additional setup after loading the view.
__weak typeof(self) weakself = self;
self.timer = [NSTimer scheduledTimerWithTimeInterval:1.0 repeats:YES block:^(NSTimer * _Nonnull timer) {
;
}];
}
- (void)func
{
NSLog(@"%s",__func__);
}
- (void)dealloc
{
NSLog(@"%s",__func__);
;
} 方法2：使用NSObject作为中间对象
Proxy1.h
@interface Proxy1 : NSObject
+ (instancetype)initWithTarget:(id)target;
@end
Proxy1.m
@interface Proxy1 ()
@property (nonatomic,weak) id target;
@end
@implementation Proxy1
+ (instancetype)initWithTarget:(id)target
{
Proxy1 *proxy = [ init];
proxy.target = target;
return proxy;
}
- (id)forwardingTargetForSelector:(SEL)aSelector
{
return self.target;
}
@end
- (void)viewDidLoad {
;
// Do any additional setup after loading the view.
self.timer = selector:@selector(func) userInfo:nil repeats:YES];
}
- (void)func
{
NSLog(@"%s",__func__);
}
- (void)dealloc
{
NSLog(@"%s",__func__);
;
} 方法3：使用NSProxy作为中间对象
Proxy2.h
@interface Proxy2 : NSProxy
+ (instancetype)initWithTarget:(id)target;
@end
Proxy2.m
@interface Proxy2 ()
@property (nonatomic,weak) id target;
@end
@implementation Proxy2
+ (instancetype)initWithTarget:(id)target
{
Proxy2 *proxy = ;
proxy.target = target;
return proxy;
}
- (NSMethodSignature *)methodSignatureForSelector:(SEL)sel
{
return ;
}
- (void)forwardInvocation:(NSInvocation *)invocation
{
;
}
@end
- (void)viewDidLoad {
;
// Do any additional setup after loading the view.
self.timer = selector:@selector(func) userInfo:nil repeats:YES];
}
- (void)func
{
NSLog(@"%s",__func__);
}
- (void)dealloc
{
NSLog(@"%s",__func__);
;
} 方法3的优点：
执行效率高，无需执行父类的方法搜索过程，直接进行消息转发。
关于NSProxy补充：
通过调用isKindOfClass
Proxy1 *proxy1 = ;
Proxy2 *proxy2 = ;
NSLog(@"%d",]); // 0
NSLog(@"%d",]); // 1 proxy1为Proxy1类型，Proxy1继承自NSObject，可以正常处理isKindOfClass方法，所以判断结果为0.
proxy2为Proxy2类型，Proxy2继承自NSProxy，大部分方法会直接进入消息转发阶段，会改为使用target进行调用，所以判断结果为1.
通过观察NSProxy的源码发现，该方法直接进行了消息转发。
/**
* Calls the -forwardInvocation: method to determine if the 'real' object
* referred to by the proxy is an instance of the specified class.
* Returns the result.<br />
* NB. The default operation of -forwardInvocation: is to raise an exception.
*/
- (BOOL) isKindOfClass: (Class)aClass
{
NSMethodSignature *sig;
NSInvocation *inv;
BOOL ret;
sig = ;
inv = ;
;
;
;
;
return ret;
}
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