一 CADisplayLink、NSTimer使用注意

• CADisplayLink吗冤、NSTimer會對target產(chǎn)生強引用又厉，如果target又對它們產(chǎn)生強引用九府，那么就會引發(fā)循環(huán)引用

示例代碼如下

• CADisplayLink

@property (strong, nonatomic) CADisplayLink *link;

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
    // 保證調用頻率和屏幕的刷幀頻率一致，60FPS
    self.link = [CADisplayLink displayLinkWithTarget:self selector:@selector(linkTest)];
    [self.link addToRunLoop:[NSRunLoop mainRunLoop] forMode:NSDefaultRunLoopMode];
}

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

執(zhí)行幾秒后點擊退出當前控制器

執(zhí)行結果如下

1653926-2b14b150ac9547df.png

由打印結果可知覆致，雖然已經(jīng)控制器已經(jīng)消失了侄旬，但是沒有調用其dealloc方法，造成內存泄露.

• NSTimer

@property (strong, nonatomic) NSTimer *timer;

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
    self.timer = [NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(timerTest) userInfo:nil repeats:YES];
    [[NSRunLoop currentRunLoop] addTimer:self.timer forMode:NSRunLoopCommonModes];
}

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

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

執(zhí)行幾秒后點擊退出當前控制器

執(zhí)行結果如下

1653926-ecf4809af703c4af.png

由運行結果可知煌妈，控制器已經(jīng)消失了儡羔，但是仍然沒有調用其dealloc方法，導致內存泄露璧诵。

解決方案

• 使用block

__weak typeof(self) weakSelf = self;
self.timer = [NSTimer scheduledTimerWithTimeInterval:1.0 repeats:YES block:^(NSTimer * _Nonnull timer) {
    [weakSelf timerTest];
}];

運行結果

1653926-fa507d3d69b333e9.png

由運行結果可知汰蜘，控制器退出時，調用了其dealloc方法之宿，不會造成內存泄露鉴扫。

• 使用代理對象（NSProxy）
• CADisplayLink

Proxy類

// Proxy.h
@interface Proxy : NSObject
+ (instancetype)proxyWithTarget:(id)target;
@property (weak, nonatomic) id target;
@end

// Proxy.m
@implementation Proxy
+ (instancetype)proxyWithTarget:(id)target {
    Proxy *proxy = [[Proxy alloc] init];
    proxy.target = target;
    return proxy;
}

- (id)forwardingTargetForSelector:(SEL)aSelector {
    return self.target;
}
@end

使用CADisplayLink

self.link = [CADisplayLink displayLinkWithTarget:[Proxy proxyWithTarget:self] selector:@selector(linkTest)];
[self.link addToRunLoop:[NSRunLoop mainRunLoop] forMode:NSDefaultRunLoopMode];

運行結果

1653926-244ab58c1b421c70.png

• NSTimer

self.timer = [NSTimer scheduledTimerWithTimeInterval:1.0 target:[Proxy proxyWithTarget:self] selector:@selector(timerTest) userInfo:nil repeats:YES];
[[NSRunLoop currentRunLoop] addTimer:self.timer forMode:NSRunLoopCommonModes];

運行結果

1653926-f64b7d101a1aa77b.png

直接繼承NSProxy

// Proxy1.h文件
@interface Proxy1 : NSProxy
+ (instancetype)proxyWithTarget:(id)target;
@property (weak, nonatomic) id target;
@end

// Proxy1.m文件
@implementation Proxy1
+ (instancetype)proxyWithTarget:(id)target {
    // NSProxy對象不需要調用init，因為它本來就沒有init方法
    Proxy1 *proxy = [Proxy1 alloc];
    proxy.target = target;
    return proxy;
}

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

- (void)forwardInvocation:(NSInvocation *)invocation {
    [invocation invokeWithTarget:self.target];
}
@end

• NSProxy的特點

Proxy *proxy1 = [Proxy proxyWithTarget:self];
Proxy1 *proxy2 = [Proxy1 proxyWithTarget:self];

NSLog(@"%d %d",[proxy1 isKindOfClass:[ViewController class]],[proxy2 isKindOfClass:[ViewController class]]);

運行結果

1653926-1370f466197b108b.png

分析：因為Proxy1是繼承自NSProxy,會直接進行消息轉發(fā)機制澈缺，所以執(zhí)行[proxy2 isKindOfClass:[ViewController class]])坪创，相當于vc執(zhí)行執(zhí)行isKindOfClass方法，而isKindOfClass內部也是進行了消息轉發(fā)姐赡，所以返回1莱预。

二 GCD定時器

• NSTimer依賴于RunLoop，如果RunLoop的任務過于繁重项滑，可能會導致NSTimer不準時
• 而GCD的定時器會更加準時

分裝GCD定時器類實例代碼如下

• CSTimer.h

@interface CSTimer : NSObject

+ (NSString *)execTask:(void(^)(void))task
                 start:(NSTimeInterval)start
              interval:(NSTimeInterval)interval
               repeats:(BOOL)repeats
                 async:(BOOL)async;

+ (NSString *)execTask:(id)target
              selector:(SEL)selector
                 start:(NSTimeInterval)start
              interval:(NSTimeInterval)interval
               repeats:(BOOL)repeats
                 async:(BOOL)async;

+ (void)cancelTask:(NSString *)name;

@end

• CSTimer.m

@implementation CSTimer

// 保存定時器的字典
static NSMutableDictionary *timers_;
// 信號量
dispatch_semaphore_t semaphore_;

// 初始化操作
+ (void)initialize {
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        timers_ = [NSMutableDictionary dictionary];
        semaphore_ = dispatch_semaphore_create(1);
    });
}

+ (NSString *)execTask:(void (^)(void))task start:(NSTimeInterval)start interval:(NSTimeInterval)interval repeats:(BOOL)repeats async:(BOOL)async {
    // 如果認為不存在 開始時間小于0 重復并且時間小于0 則返回空
    if (!task || start < 0 || (interval <= 0 && repeats)) return nil;

    // 隊列 - 是主隊列還是并發(fā)隊列
    dispatch_queue_t queue = async ? dispatch_get_global_queue(0, 0) : dispatch_get_main_queue();

    // 創(chuàng)建定時器
    dispatch_source_t timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue);

    // 設置時間
    dispatch_source_set_timer(timer,
                              dispatch_time(DISPATCH_TIME_NOW, start * NSEC_PER_SEC),
                              interval * NSEC_PER_SEC, 0);

    // 保證線程安全
    dispatch_semaphore_wait(semaphore_, DISPATCH_TIME_FOREVER);
    // 定時器的唯一標識
    NSString *name = [NSString stringWithFormat:@"%zd", timers_.count];
    // 存放到字典中
    timers_[name] = timer;
    dispatch_semaphore_signal(semaphore_);

    // 設置回調
    dispatch_source_set_event_handler(timer, ^{
        task();

        if (!repeats) { // 不重復的任務
            [self cancelTask:name];
        }
    });

    // 啟動定時器
    dispatch_resume(timer);

    return name;
}

+ (NSString *)execTask:(id)target selector:(SEL)selector start:(NSTimeInterval)start interval:(NSTimeInterval)interval repeats:(BOOL)repeats async:(BOOL)async {
    if (!target || !selector) return nil;

    return [self execTask:^{
        if ([target respondsToSelector:selector]) {
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Warc-performSelector-leaks"
            [target performSelector:selector];
#pragma clang diagnostic pop
        }
    } start:start interval:interval repeats:repeats async:async];
}

// 取消定時器操作
+ (void)cancelTask:(NSString *)name {
    if (name.length == 0) return;

    // 線程安全
    dispatch_semaphore_wait(semaphore_, DISPATCH_TIME_FOREVER);

    dispatch_source_t timer = timers_[name];
    if (timer) {
        dispatch_source_cancel(timer);
        [timers_ removeObjectForKey:name];
    }

    dispatch_semaphore_signal(semaphore_);
}

外部調用

// 開始定時器操作
- (void)startTimer {
    // 1.使用block回調
    self.task = [CSTimer execTask:^{
        NSLog(@"111111 - %@", [NSThread currentThread]);
    } start:2.0 interval:1.0 repeats:YES async:YES];

    // 2.使用selector
//    self.task = [CSTimer execTask:self selector:@selector(doTask) start:2.0 interval:1.0 repeats:YES async:YES];
}

// 定時執(zhí)行任務
- (void)doTask {
    NSLog(@"doTask - %@", [NSThread currentThread]);
}

// 停止定時器
[CSTimer cancelTask:self.task];

本文參考:
路飛_Luck (http://www.reibang.com/p/07f7b96bb03f)
以及借鑒MJ的教程視頻
非常感謝.

項目連接地址 - MemoryManage-CADisplayLink+Timer