NSProxy.h文件内容

#import <Foundation/NSObject.h>

@class NSMethodSignature, NSInvocation;

NS_ASSUME_NONNULL_BEGIN

NS_ROOT_CLASS
@interface NSProxy <NSObject> {
    Class   isa;
}

+ (id)alloc;
+ (id)allocWithZone:(nullable NSZone *)zone NS_AUTOMATED_REFCOUNT_UNAVAILABLE;
+ (Class)class;

- (void)forwardInvocation:(NSInvocation *)invocation;
- (nullable NSMethodSignature *)methodSignatureForSelector:(SEL)sel NS_SWIFT_UNAVAILABLE("NSInvocation and related APIs not available");
- (void)dealloc;
- (void)finalize;
@property (readonly, copy) NSString *description;
@property (readonly, copy) NSString *debugDescription;
+ (BOOL)respondsToSelector:(SEL)aSelector;

- (BOOL)allowsWeakReference NS_UNAVAILABLE;
- (BOOL)retainWeakReference NS_UNAVAILABLE;

// - (id)forwardingTargetForSelector:(SEL)aSelector;

@end

NS_ASSUME_NONNULL_END

NSProxy 是一个抽象类
NSProxy遵守了 NSObject 协议，内部有它的 isa 指针
NSProxy 的使用需要实现两个方法：

- (void)forwardInvocation:(NSInvocation *)invocation;
- (nullable NSMethodSignature *)methodSignatureForSelector:(SEL)sel

• 解决NSTimer循环引用（使用 NSProxy 持有 NSTimer 的 target）

#import "WeakProxy.h"

@interface WeakProxy ()

@property (weak,nonatomic,readonly)id target;

+ (instancetype)proxyWithTarget:(id)target;

- (instancetype)initWithTarget:(id)target;

@end

@implementation WeakProxy

- (instancetype)initWithTarget:(id)target{
    _target = target;
    return self;
}

+ (instancetype)proxyWithTarget:(id)target{
    return [[self alloc] initWithTarget:target];
}
//转发消息
- (void)forwardInvocation:(NSInvocation *)invocation{
    SEL sel = [invocation selector];
    if ([self.target respondsToSelector:sel]) {
        [invocation invokeWithTarget:self.target];
    }
}

- (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector{
    return [self.target methodSignatureForSelector:aSelector];
}

- (BOOL)respondsToSelector:(SEL)aSelector{
    return [self.target respondsToSelector:aSelector];
}

@end

文件内使用代码

- (void)viewDidLoad {
    [super viewDidLoad];
 
    self.timer = [NSTimer timerWithTimeInterval:1 target:[WeakProxy proxyWithTarget:self] selector:@selector(timerEvent) userInfo:nil repeats:YES];
    [[NSRunLoop mainRunLoop] addTimer:self.timer forMode:NSRunLoopCommonModes];
}

- (void)timerEvent {
    static NSInteger num = 0;
    NSLog(@"%zd", num ++);
}

- (void)dealloc{
    NSLog(@"dealloc");
    [self.timer invalidate];
}