一、CADisplayLink、NSTimer使用注意
- CADisplayLink、NSTimer会对target产生强引用，如果target又对它们产生强引用，那么就会引发循环引用
示例代码如下
CADisplayLink
@property (strong, nonatomic) CADisplayLink *link;
- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
// 保证调用频率和屏幕的刷帧频率一致，60FPS
self.link = [CADisplayLink displayLinkWithTarget:self selector:@selector(linkTest)];
[self.link addToRunLoop:[NSRunLoop mainRunLoop] forMode:NSDefaultRunLoopMode];
}
- (void)linkTest {
NSLog(@"%s", __func__);
}
执行几秒后点击退出当前控制器
执行结果如下
由打印结果可知，虽然已经控制器已经消失了，但是没有调用其
dealloc方法，造成内存泄露.
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];
}
执行几秒后点击退出当前控制器
执行结果如下
由运行结果可知，控制器已经消失了，但是仍然没有调用其
dealloc方法，导致内存泄露。
解决方案
- 使用block
__weak typeof(self) weakSelf = self;
self.timer = [NSTimer scheduledTimerWithTimeInterval:1.0 repeats:YES block:^(NSTimer * _Nonnull timer) {
[weakSelf timerTest];
}];
运行结果
由运行结果可知，控制器退出时，调用了其
dealloc方法，不会造成内存泄露。
- 使用代理对象
Proxy类
// 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];
运行结果
使用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];
运行结果
- 直接继承
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对象不需要调用init，因为它本来就没有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的特点
Proxy *proxy1 = [Proxy proxyWithTarget:self];
Proxy1 *proxy2 = [Proxy1 proxyWithTarget:self];
NSLog(@"%d %d",[proxy1 isKindOfClass:[ViewController class]],[proxy2 isKindOfClass:[ViewController class]]);
运行结果
image
分析：因为
Proxy1是继承自NSProxy,会直接进行消息转发机制，所以执行[proxy2 isKindOfClass:[ViewController class]])，相当于vc执行执行isKindOfClass方法，而isKindOfClass内部也是进行了消息转发，所以返回1。
二、GCD定时器
- NSTimer依赖于RunLoop，如果RunLoop的任务过于繁重，可能会导致NSTimer不准时
- 而GCD的定时器会更加准时
封装GCD定时器类实例代码如下
- 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
// 保存定时器的字典
static NSMutableDictionary *timers_;
// 信号量
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 {
// 如果认为不存在 开始时间小于0 重复并且时间小于0 则返回空
if (!task || start < 0 || (interval <= 0 && repeats)) return nil;
// 队列 - 是主队列还是并发队列
dispatch_queue_t queue = async ? dispatch_get_global_queue(0, 0) : dispatch_get_main_queue();
// 创建定时器
dispatch_source_t timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue);
// 设置时间
dispatch_source_set_timer(timer,
dispatch_time(DISPATCH_TIME_NOW, start * NSEC_PER_SEC),
interval * NSEC_PER_SEC, 0);
// 保证线程安全
dispatch_semaphore_wait(semaphore_, DISPATCH_TIME_FOREVER);
// 定时器的唯一标识
NSString *name = [NSString stringWithFormat:@"%zd", timers_.count];
// 存放到字典中
timers_[name] = timer;
dispatch_semaphore_signal(semaphore_);
// 设置回调
dispatch_source_set_event_handler(timer, ^{
task();
if (!repeats) { // 不重复的任务
[self cancelTask:name];
}
});
// 启动定时器
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];
}
// 取消定时器操作
+ (void)cancelTask:(NSString *)name {
if (name.length == 0) return;
// 线程安全
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_);
}
- 外部调用
// 开始定时器操作
- (void)startTimer {
// 1.使用block回调
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];
}
// 定时执行任务
- (void)doTask {
NSLog(@"doTask - %@", [NSThread currentThread]);
}
// 停止定时器
[CSTimer cancelTask:self.task];
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