前语

在开发中难免使用到NSTimer，为了避免循环引用，可能会在willDismiss来进行释放，置为nil；不过经过查阅大神资料，有更好的解决方法:NSProxy;
下面来介绍一下

实现

先上代码：MyTimerProxy.h

#import <Foundation/Foundation.h>

NS_ASSUME_NONNULL_BEGIN

@interface MyTimerProxy : NSObject

@property (nonatomic, weak) id target;
+ (instancetype)initWithTarget:(id)target;

@end

MyTimerProxy.m

//
//  MyTimerProxy.m
//  Test-OC
//
//  Created by Old.Wang on 2020/11/9.
//  Copyright © 2020 Old.Wang. All rights reserved.
//

#import "MyTimerProxy.h"

@implementation MyTimerProxy

+ (instancetype)initWithTarget:(id)target{
    MyTimerProxy * proxy = [[MyTimerProxy alloc] init];
    proxy.target = target;
    return proxy;
}

- (void)forwardInvocation:(NSInvocation *)anInvocation{
    if ([self.target respondsToSelector:anInvocation.selector]) {
        [anInvocation invokeWithTarget:self.target];
    }
}

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

@end

Controller层使用以及日志

#import "ViewController.h"
#import "MyTimerProxy.h"

@interface ViewController ()

@property (nonatomic, strong) NSTimer  * t_timer;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    
    MyTimerProxy *myProxy = [MyTimerProxy initWithTarget:self];
    self.t_timer = [NSTimer timerWithTimeInterval:3 target:myProxy selector:@selector(runTimer) userInfo:nil repeats:YES];
    [[NSRunLoop mainRunLoop] addTimer:self.t_timer forMode:NSRunLoopCommonModes];
    
}

#pragma mark - timer
- (void)runTimer{
    NSLog(@"Runing %s",__func__);
}

#pragma mark - Dealloc
- (void)dealloc{
    [self.t_timer invalidate];
    self.t_timer = nil;
    
    NSLog(@"%s",__func__);
}

@end

离开页面栈后，最后打印日志为：[viewController dealloc]，对象释放；

原理

NSProxy解决循环引用原理图.png

实际上通过弱化self - target 的强引用关系来解决引用环。