NSTimer

Timer的模拟使用

计时器一个很常用的场景就是，打开一个页面，页面中有一个banner使用计时器来自动翻页。在退出页面时，我们希望退出页面时，这个计时器能够停止工作，并且页面对象能够被销毁

TimerObj

// TimerObj.h
@interface TimerObj : NSObject
@property (nonatomic, strong, nullable) NSTimer *timer1;
+ (TimerObj *)object;

- (void)printLog;
- (void)printFinish;

- (void)beginLog;
- (void)beginLogWeak;

@end

@implementation TimerObj
+ (TimerObj *)object{
    return [[TimerObj alloc] init];
}

#pragma mark - log
- (void)printLog{
    static int idx = 0;
    NSLog(@"msg: %d", ++idx);
}
- (void)printFinish{
    NSLog(@"msg finish!!");
}

- (void)dealloc {
    [self.timer1 invalidate];
    self.timer1 = nil;
    NSLog(@"%s", __func__);
}
@end

Test

// TimerObj
- (void)beginLog{
    if (!self.timer1) {
        self.timer1 = [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(printLog) userInfo:nil repeats:YES];
    }
    [self.timer1 fire];
}

void classTimerCommon () {
    @autoreleasepool {
        TimerObj *obj = [TimerObj object];
        [obj beginLog];
        dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 4*NSEC_PER_SEC), dispatch_get_main_queue(), ^{
            [obj printFinish];
        });
    }
}

我们创建了TimerObj,调用- beginLog方法模拟view展示。同时模拟4秒后退出界面

• 日志输出

 Hello, World!
 msg: 1
 msg: 2
 msg: 3
 msg: 4
 msg: 5
 msg finish!!
 msg: 6
 msg: 7
 msg: 8

• 结论
  • 计时器并没有停止，obj也没有被销毁

可能尝试使用weakSelf来结局问题，单理想很美满，显示却很惨

// TimerObj
- (void)beginLogWeak{
    if (!self.timer1) {
        __weak typeof(self) weakSelf = self;
        self.timer1 = [NSTimer scheduledTimerWithTimeInterval:1 target:weakSelf selector:@selector(printLog) userInfo:nil repeats:YES];
    }
    [self.timer1 fire];
}

void classTimerWeakSelf () {
    @autoreleasepool {
        TimerObj *obj = [TimerObj object];
        [obj beginLogWeak];
        dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 4*NSEC_PER_SEC), dispatch_get_main_queue(), ^{
            [obj printFinish];
        });
    }
}

• 日志输出

 Hello, World!
 msg: 1
 msg: 2
 msg: 3
 msg: 4
 msg: 5
 msg finish!!
 msg: 6
 msg: 7

使用一个对象来中转能够解决，但是却不那么优雅

// TimerObjWeak
@interface TimerObjWeak : NSObject
@property (nonatomic, weak) TimerObj *weakObj;
@end
@implementation TimerObjWeak
- (void)printOtherLog{
    [self.weakObj printLog];
}
- (void)dealloc {
    NSLog(@"%s", __func__);
}
@end
  
// TimerObj
- (void)beginLogOtherWeak{
    if (!self.timer1) {
        TimerObjWeak *otherObj = [[TimerObjWeak alloc] init];
        otherObj.weakObj = self;
        self.timer1 = [NSTimer scheduledTimerWithTimeInterval:1 target:otherObj selector:@selector(printOtherLog) userInfo:nil repeats:YES];
    }
    [self.timer1 fire];
}

void classTimerWeakOther () {
    @autoreleasepool {
        TimerObj *obj = [TimerObj object];
        [obj beginLogOtherWeak];
        dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 4*NSEC_PER_SEC), dispatch_get_main_queue(), ^{
            [obj printFinish];
        });
    }
}

• 日志输出

 Hello, World!
 msg: 1
 msg: 2
 msg: 3
 msg: 4
 msg: 5
 msg finish!!
 -[TimerObjWeak dealloc]
 -[TimerObj dealloc]

• 结论
  • 两个对象都进行了释放

使用另一个对象来解决timer循环引用是可行的，但是不那么优雅。它引入了一个新的方法- printOtherLog。如果有多个类似TimerObj这样的对象，简直是可怕。使用NSProxy能非常优雅的解决这个问题

NSProxy

NSProxy很强大，这里只举例来解决Timer循环引用

• TimerProxy

@interface TimerProxy: NSProxy
@property(nonatomic,weak)id target;
@end

@implementation TimerProxy
-(instancetype)initWithTarget:(id)target{
    self.target = target;
    return self;
}
+(instancetype)proxyWithTarget:(id)target{
    return [[self alloc] initWithTarget:target];
}
-(NSMethodSignature *)methodSignatureForSelector:(SEL)sel{
    // 在具体的子类中重写此方法，为给定的选择器和代理对象所代表的类返回正确的对象
    return [self.target methodSignatureForSelector:sel];
}
-(void)forwardInvocation:(NSInvocation *)invocation{
    // 将给定的调用传递给代理表示的真实对象。
    SEL sel = invocation.selector;
    if ([self.target respondsToSelector:sel]) {
        [invocation invokeWithTarget:self.target];
    }
}
@end

// 
- (void)beginLogProxy{
    if (!self.timer1) {
        self.timer1 = [NSTimer scheduledTimerWithTimeInterval:1 target:[TimerProxy proxyWithTarget:self] selector:@selector(printLog) userInfo:nil repeats:YES];
    }
    [self.timer1 fire];
}

void classTimerProxy () {
    @autoreleasepool {
        TimerObj *obj = [TimerObj object];
        [obj beginLogProxy];
        dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 4*NSEC_PER_SEC), dispatch_get_main_queue(), ^{
            [obj printFinish];
        });
    }
}

• 日志输出

 Hello, World!
 msg: 1
 msg: 2
 msg: 3
 msg: 4
 msg: 5
 msg finish!!
 -[TimerObj dealloc]

Timer的模式

Apple的解释

• NSRunLoopCommonModes

  Objects added to a run loop using this value as the mode are monitored by all run loop modes that have been declared as a member of the set of “common" modes; see the description of CFRunLoopAddCommonMode

• NSDefaultRunLoopMode

  The mode to deal with input sources other than NSConnection

• NSEventTrackingRunLoopMode

  A run loop should be set to this mode when tracking events modally, such as a mouse-dragging loop.

• NSModalPanelRunLoopMode

  A run loop should be set to this mode when waiting for input from a modal panel, such as NSSavePanel or NSOpenPanel.

• UITrackingRunLoopMode

  The mode set while tracking in controls takes place.