CADisplayLink、NSTimer循环引用解决方案

前言:CADisplayLink、NSTimer 循环引用问题

​ CADisplayLink、NSTimer会对Target产生强引用,如果target又对他们产生强引用,那么就会引发循环引用。

@interface ViewController ()

@property (nonatomic, strong) CADisplayLink *link;
@property (nonatomic, strong) NSTimer *time;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    // 保证调用频率和刷帧频率 60fps
    self.link = [CADisplayLink displayLinkWithTarget:self selector:@selector(linkTest)];
    [self.link addToRunLoop:[NSRunLoop mainRunLoop] forMode:NSDefaultRunLoopMode] ;
    
    self.time = [NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(timeTest) userInfo:nil repeats:YES]; 
}

- (void)timeTest {
    NSLog(@"%s", __func__);
}

- (void)linkTest {
    NSLog(@"%s", __func__);
}

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
    NSLog(@"%s", __func__);
    [self.time invalidate];
}

__weak typeof(self) weakSelf = self;能否解决NSTimer的循环引用问题?

答:我们并不能够通过__weak typeof(self) weakSelf = self;代码来实现解决循环引用。

__weak typeof(self) weakSelf = self;是用在block内可以解决循环引用的问题。

​ NSTime 使用提供 block 的 API ,通过 __weak 解决循序引用问题

- (void)viewDidLoad {
    [super viewDidLoad];
    
    __weak typeof(self) weakSelf = self;
    self.time = [NSTimer scheduledTimerWithTimeInterval:1.0 repeats:YES block:^(NSTimer * _Nonnull timer) {
        [weakSelf timeTest];
    } ];
}

- (void)timeTest {
    NSLog(@"%s", __func__);
}

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
    NSLog(@"%s", __func__);
    [self.time invalidate];
}

方案二、使用 NSObject 消息转发

​ 通过中间变量,是中间的一个引用变成弱引用。

​ 第一步:创建继承 NSObject 的 RHMiddleTarget 中间文件,创建 target 属性,使用 weak 弱引用修饰

#import <Foundation/Foundation.h>

@interface RHMiddleTarget : NSObject

@property (nonatomic, weak) id target;

+ (instancetype)middleTargetWithTarget:(id)target;

@end


#import "RHMiddleTarget.h"

@implementation RHMiddleTarget

+ (instancetype)middleTargetWithTarget:(id)target {
    RHMiddleTarget *middleTarget = [[RHMiddleTarget alloc] init];
    middleTarget.target = target;
    return middleTarget;
}

- (id)forwardingTargetForSelector:(SEL)aSelector {
    // 返回可以处理的对象, 给对象发送aSelector消息
    // objc_msgSend(self.target, aSelector);
    return self.target;
}

@end

第二步:在使用 CADisplayLink 和 NSTimer 中的 target 传到中间变量里:

    // 保证调用频率和刷帧频率 60fps
    self.link = [CADisplayLink displayLinkWithTarget:[RHMiddleTarget middleTargetWithTarget:self] selector:@selector(linkTest)];
    [self.link addToRunLoop:[NSRunLoop mainRunLoop] forMode:NSDefaultRunLoopMode] ;
    
    self.time = [NSTimer scheduledTimerWithTimeInterval:1.0 target:[RHMiddleTarget middleTargetWithTarget:self] selector:@selector(timeTest) userInfo:nil repeats:YES];

第三步:测试验证:

2022-07-05 16:01:47.895716+0800 Interview03-定时器[10828:260303] -[ViewController timeTest]
2022-07-05 16:01:48.895649+0800 Interview03-定时器[10828:260303] -[ViewController timeTest]
2022-07-05 16:01:49.895571+0800 Interview03-定时器[10828:260303] -[ViewController timeTest]
2022-07-05 16:01:50.666056+0800 Interview03-定时器[10828:260303] -[ViewController touchesBegan:withEvent:]

方案三、使用 NSProxy 消息转发

第一步:创建继承 NSObject 的 RHMiddleTarget 中间文件,创建 target 属性,使用 weak 弱引用修饰

#import <Foundation/Foundation.h>

@interface RHMiddleTarget : NSProxy

@property (nonatomic, weak) id target;

+ (instancetype)middleTargetWithTarget:(id)target;

@end

#import "RHMiddleTarget.h"

@implementation RHMiddleTarget

+ (instancetype)middleTargetWithTarget:(id)target {
    RHMiddleTarget *middleTarget = [RHMiddleTarget alloc];
    middleTarget.target = target;
    return middleTarget;
}

// 返回方法签名
- (NSMethodSignature *)methodSignatureForSelector:(SEL)sel {
    return [self.target methodSignatureForSelector:sel];
}

// 进行相应的调用
- (void)forwardInvocation:(NSInvocation *)invocation {
    [invocation invokeWithTarget:self.target];
}

第二步:在使用 CADisplayLink 和 NSTimer 中的 target 传到中间变量里

    // 保证调用频率和刷帧频率 60fps
    self.link = [CADisplayLink displayLinkWithTarget:[RHMiddleTarget middleTargetWithTarget:self] selector:@selector(linkTest)];
    [self.link addToRunLoop:[NSRunLoop mainRunLoop] forMode:NSDefaultRunLoopMode] ;
    
    self.time = [NSTimer scheduledTimerWithTimeInterval:1.0 target:[RHMiddleTarget middleTargetWithTarget:self] selector:@selector(timeTest) userInfo:nil repeats:YES];

第三步:测试验证

2022-07-05 16:27:25.427454+0800 Interview03-定时器[11550:281823] -[ViewController linkTest]
2022-07-05 16:27:25.444101+0800 Interview03-定时器[11550:281823] -[ViewController linkTest]
2022-07-05 16:27:25.456983+0800 Interview03-定时器[11550:281823] -[ViewController touchesBegan:withEvent:]

方案四、使用 viewWillDisappear

​ 在控制器销毁或者定时器停止的时候,调用如下的方法

 [self.timer invalidate];
 [self.link invalidate];
 self.timer = nil;
 self.link = nil;

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