內(nèi)存管理 01 - NSTimer、CADisplayLink、GCD 定時(shí)器

內(nèi)存管理 01 - NSTimer、CADisplayLink、GCD 定時(shí)器

使用 NSTimer、CADisplayLink 需要注意什么？

NSTimer、CADisplayLink 在失效前會(huì)一直對(duì) target 產(chǎn)生強(qiáng)引用，導(dǎo)致 target 沒(méi)法釋放。

NSTimer 的解決方式有三種：使用 NSProxy 中間對(duì)象、使用包裝類、通過(guò) Category 擴(kuò)展 NSTimer。
CADisplayLink 的解決方式有兩種：使用 NSProxy 中間對(duì)象、使用包裝類。

1. 使用 NSProxy 中間對(duì)象

  1. 將 NSTimer 的 target 指定為 NSProxy，NSProxy 中對(duì) 真正的 target 進(jìn)行弱引用。
  2. NSProxy 中利用消息轉(zhuǎn)發(fā)機(jī)制調(diào)用真正的 target 的 Selector;

使用 NSProxy 的優(yōu)勢(shì)：

  • NSProxy 在消息發(fā)送階段不會(huì)到父類中查找方法
  • 消息發(fā)送失敗后也不會(huì)嘗試動(dòng)態(tài)方法解析。
  • 消息發(fā)送失敗后直接進(jìn)行消息轉(zhuǎn)發(fā)，并且直接調(diào)用 methodSignatureForSelector: 方法。

TargetProxy

@interface TargetProxy : NSProxy

@property (nonatomic, weak) id target;

+ (instancetype)targetProxyWithTarget:(id)target;
+ 
@end

@implementation TargetProxy

+ (instancetype)targetProxyWithTarget:(id)target {
    TargetProxy *proxy = [self alloc];
    proxy.target = target;
    return proxy;
}

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

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

@end

TargetProxy 使用示例

@interface ViewController ()

@property (nonatomic, strong) NSTimer *timer;
@property (nonatomic, strong) CADisplayLink *displayLink;

@end

@implementation ViewController

- (void)dealloc {
    [self.timer invalidate];
    [self.displayLink invalidate];
}

- (void)viewDidLoad {
    [super viewDidLoad];

    self.timer = [NSTimer scheduledTimerWithTimeInterval:1.0
                                                  target:[TargetProxy targetProxyWithTarget:self]
                                                selector:@selector(doWork)
                                                userInfo:nil
                                                 repeats:YES];

    self.displayLink = [CADisplayLink displayLinkWithTarget:[TargetProxy targetProxyWithTarget:self]
                                                   selector:@selector(doWork)];
    [self.displayLink addToRunLoop:[NSRunLoop currentRunLoop] forMode:NSRunLoopCommonModes];
}

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

@end

2. 包裝 CADisplayLink、NSTimer

  1. 將 NSTimer、CADisplayLink 作為屬性包裝到自定義類中。
  2. 通過(guò)包裝類對(duì)外提供 NSTimer、CADisplayLink 的功能。

NoRetainTimer

@interface NoRetainTimer : NSObject

@property (nonatomic, readonly, getter=isValid) BOOL valid;

+ (instancetype)scheduledTimerWithTimeInterval:(NSTimeInterval)interval
                                       repeats:(BOOL)repeats
                                         block:(void (^)(NSTimer *timer))block;

- (void)addToRunLoop:(NSRunLoop *)runloop forMode:(NSRunLoopMode)mode;
- (void)invalidate;

@end

@interface NoRetainTimer ()

@property (nonatomic, strong) NSTimer *timer;

@end

@implementation NoRetainTimer

- (void)dealloc {
    [self invalidate];
}

- (BOOL)isValid {
    return self.timer.isValid;
}

+ (instancetype)scheduledTimerWithTimeInterval:(NSTimeInterval)interval
                                       repeats:(BOOL)repeats
                                         block:(void (^)(NSTimer *timer))block {
    NoRetainTimer *instance = [[NoRetainTimer alloc] init];
    instance.timer = [NSTimer scheduledTimerWithTimeInterval:interval
                                                      target:self
                                                    selector:@selector(__blockInvokeWithTimer:)
                                                    userInfo:[block copy]
                                                     repeats:repeats];
    return instance;
}

- (void)addToRunLoop:(NSRunLoop *)runloop forMode:(NSRunLoopMode)mode {
    [runloop addTimer:self.timer forMode:mode];
}

- (void)invalidate {
    [self.timer invalidate];
}

+ (void)__blockInvokeWithTimer:(NSTimer *)timer {
    void (^block)(NSTimer *timer) = timer.userInfo;
    if (block) {
        block(timer);
    }
}

@end

NoRetainDisplayLink

@interface NoRetainDisplayLink : NSObject

@property (nonatomic, readonly, getter=isValid) BOOL valid;

+ (instancetype)displayLinkWithBlock:(void(^)(NoRetainDisplayLink *displayLink))block;

- (void)addToRunLoop:(NSRunLoop *)runloop forMode:(NSRunLoopMode)mode;
- (void)removeFromRunLoop:(NSRunLoop *)runloop forMode:(NSRunLoopMode)mode;

- (void)invalidate;

@end

@interface NoRetainDisplayLink ()

@property (nonatomic, strong) CADisplayLink *displayLink;
@property (nonatomic, readwrite, getter=isValid) BOOL valid;
@property (nonatomic, copy) void (^block)(NoRetainDisplayLink *displayLink);

@end

@implementation NoRetainDisplayLink

- (void)dealloc {
    [self invalidate];
}

- (BOOL)isPaused {
    return self.displayLink;
}

+ (instancetype)displayLinkWithBlock:(void(^)(NoRetainDisplayLink *displayLink))block {
    NoRetainDisplayLink *instance = [[self alloc] init];
    instance.valid = YES;
    instance.block = block;
    instance.displayLink = [CADisplayLink displayLinkWithTarget:instance selector:@selector(__blockInvoke)];
    return instance;
}

- (void)addToRunLoop:(NSRunLoop *)runloop forMode:(NSRunLoopMode)mode {
    [self.displayLink addToRunLoop:runloop forMode:NSRunLoopCommonModes];
}

- (void)removeFromRunLoop:(NSRunLoop *)runloop forMode:(NSRunLoopMode)mode {
    [self.displayLink removeFromRunLoop:runloop forMode:NSRunLoopCommonModes];
}

- (void)invalidate {
    instance.valid = NO;
    [self.displayLink invalidate];
}

- (void)__blockInvoke {
    self.block(self);
}

@end

NoRetainTimer & NoRetainDisplayLink 使用示例

@interface ViewController ()

@property (nonatomic, strong) NoRetainTimer *timer;
@property (nonatomic, strong) NoRetainDisplayLink *displayLink;

@end

@implementation ViewController

- (void)dealloc {
    [self.timer invalidate];
    [self.displayLink invalidate];
}

- (void)viewDidLoad {
    [super viewDidLoad];

    self.timer = [NoRetainTimer scheduledTimerWithTimeInterval:1.0
                                                       repeats:YES
                                                         block:^(NSTimer *timer) {
                                                             NSLog(@"%s", __func__);
                                                         }];

    self.displayLink = [NoRetainDisplayLink displayLinkWithBlock:^(NoRetainDisplayLink *displayLink) {
        NSLog(@"%s", __func__);
    }];
    [self.displayLink addToRunLoop:[NSRunLoop currentRunLoop] forMode:NSRunLoopCommonModes];
}

@end

3. 通過(guò) Category 擴(kuò)展 NSTimer

  1. 創(chuàng)建一個(gè) NSTimer 的分類，提供一個(gè) +scheduledTimerWithTimeInterval:repeats:block 方法。
  2. 將 NSTimer 的 target 指定為 [NSTimer class]，selector 為 Category 中的一個(gè)類方法，并將 block 作為 NSTimer 的 userInfo。
  3. 當(dāng) Category 的類方法被 NSTimer 回調(diào)時(shí)，取出 NSTimer 中的 block（userInfo），調(diào)用 block。

NSTimer+NoRetain

@interface NSTimer (NoRetain)

+ (instancetype)noretain_scheduledTimerWithTimeInterval:(NSTimeInterval)ti
                                                repeats:(BOOL)repeats
                                                  block:(void (^)(NSTimer *timer))block;

@end

@implementation NSTimer (NoRetain)

+ (instancetype)noretain_scheduledTimerWithTimeInterval:(NSTimeInterval)ti
                                                repeats:(BOOL)repeats
                                                  block:(void (^)(NSTimer *timer))block {
    return [self scheduledTimerWithTimeInterval:ti
                                         target:self
                                       selector:@selector(__blockInvokeWithTimer:)
                                       userInfo:[block copy]
                                        repeats:repeats];
}

+ (void)__blockInvokeWithTimer:(NSTimer *)timer {
    void (^block)(NSTimer *timer) = timer.userInfo;
    if (block) {
        block(timer);
    }
}
@end

NSTimer+NoRetain 使用示例

@interface ViewController ()

@property (nonatomic, strong) NSTimer *timer;

@end

@implementation ViewController

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

- (void)viewDidLoad {
    [super viewDidLoad];
    self.timer = [NSTimer noretain_scheduledTimerWithTimeInterval:1.0
                                                          repeats:YES
                                                            block:^(NSTimer *timer) {
                                                                NSLog(@"%s", __func__);
                                                            }];
}

@end

GCD 定時(shí)器

  • NSTimer 依賴于 RunLoop，當(dāng) RunLoop 的任務(wù)過(guò)于繁重時(shí)，可能會(huì)導(dǎo)致 NSTimer 不準(zhǔn)時(shí)。
  • GCD 定時(shí)器基于內(nèi)核，不依賴于 RunLoop，時(shí)間調(diào)度會(huì)非常準(zhǔn)時(shí)。

GCDTimer 實(shí)現(xiàn)

@interface GCDTimer : NSObject

@property (nonatomic, readonly, getter=isValid) BOOL valid;

+ (instancetype)scheduledTimerWithTimeInterval:(NSTimeInterval)interval
                                       repeats:(BOOL)repeats
                                  inBackground:(BOOL)background
                                         block:(void (^)(GCDTimer *timer))block;


- (void)invalidate;

@end

@interface GCDTimer ()

@property (nonatomic, strong) dispatch_source_t timer;
@property (nonatomic, readwrite, getter=isValid) BOOL valid;
@property (nonatomic, copy) void (^block)(GCDTimer *displayLink);

@end


@implementation GCDTimer

- (void)dealloc {
    [self invalidate];
}

+ (instancetype)scheduledTimerWithTimeInterval:(NSTimeInterval)interval
                                       repeats:(BOOL)repeats
                                  inBackground:(BOOL)background
                                         block:(void (^)(GCDTimer *timer))block {
    GCDTimer *instance = [[GCDTimer alloc] init];

    // 隊(duì)列
    dispatch_queue_t taskQueue = background
    ? dispatch_queue_create([GCDTimer.description cStringUsingEncoding:NSUTF8StringEncoding], DISPATCH_QUEUE_SERIAL)
    : dispatch_get_main_queue();
    
    // 創(chuàng)建定時(shí)器
    dispatch_source_t timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, taskQueue);

    // 設(shè)置時(shí)間
    dispatch_source_set_timer(timer,
                              dispatch_time(DISPATCH_TIME_NOW, NSEC_PER_SEC * interval),
                              NSEC_PER_SEC * interval, 0);;

    // 設(shè)置回調(diào)
    __weak typeof(instance) weakInstance = instance;
    dispatch_source_set_event_handler(timer, ^{
        weakInstance.block(weakInstance);

        // 不重復(fù)
        if (!repeats) {
            [weakInstance invalidate];
        }
    });

    // 啟動(dòng)定時(shí)器
    instance.timer = timer;
    instance.block = block;
    instance.valid = YES;
    dispatch_resume(timer);
    return instance;
}

- (void)invalidate {
    self.valid = NO;
    dispatch_cancel(self.timer);
}

GCDTimer 使用示例

@interface ViewController ()

@property (nonatomic, strong) GCDTimer *timer;

@end

@implementation ViewController

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

- (void)viewDidLoad {
    [super viewDidLoad];
    
    self.timer = [GCDTimer scheduledTimerWithTimeInterval:1.0 repeats:YES inBackground:YES block:^(GCDTimer *timer) {
        NSLog(@"%s", __func__);
    }];
}

@end
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