背景
公司的一个UIWebView要加个进度条，但是UIWebView没有进度啊。所以做个假的，用定时器。但是发现来回的进UIWebView的控制器，会崩溃。发现是在NSTimer那里崩溃的。那是因为NSTimer导致内存泄漏了。先说说为什么会发生内存泄漏吧。
写个小栗子🌰。
//
// ViewController.m
// timer
//
// Created by wyb on 2017/4/12.
// Copyright © 2017年 中天易观. All rights reserved.
//
#import "ViewController.h"
#import "TimeViewController.h"
@interface ViewController ()
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
}
- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
TimeViewController *vc = [[TimeViewController alloc]init];
[self presentViewController:vc animated:YES completion:nil];
}
@end
#import "TimeViewController.h"
@interface TimeViewController ()
@property(nonatomic,weak)NSTimer *timer;
@end
@implementation TimeViewController
- (void)viewDidLoad {
[super viewDidLoad];
self.view.backgroundColor = [UIColor greenColor];
self.timer = [NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(timeAction:) userInfo:nil repeats:YES];
}
- (void)timeAction:(NSTimer *)timer {
NSLog(@"%s",__func__);
}
- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
[self dismissViewControllerAnimated:YES completion:nil];
}
发现个问题，当我跳到TimeViewController控制器的时候，定时器干活了。当我点击屏幕开始dismissViewController它的时候，发现定时器还在干活。那就是timer没停止。
delloc方法里销毁它。
- (void)dealloc
{
[self.timer invalidate];
self.timer = nil;
}
发现不起作用。我就是遇到这个问题导致的内存泄漏。本以为把它销毁了。然而并没有卵用。dealloc根本没走。
根源
@property(nonatomic,weak)NSTimer *timer;
self.timer = [NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(timeAction:) userInfo:nil repeats:YES];
timer创建成功会被添加到Runloop里，它就被Runloop强引用了。它的target是self。所以它强引用了self。属性那里是weak没事。
当我们想销毁TimeViewController的时候，因为它被timer强引用所以它销毁不了。多会timer死了，它才能死。但是它要是死不了delloc方法不会走。delloc方法走不了timer就死不了。只有执行了[self.timer invalidate]，timer才会死。所以这就是循环引用了。
解决1
__weak typeof(self) weakSelf = self;
self.timer = [NSTimer scheduledTimerWithTimeInterval:1.0 target:weakSelf selector:@selector(timeAction:) userInfo:nil repeats:YES];
发现不起作用。还是引用self。这个里面表面看着可以，但是内部肯定还强引用。我这里也不太明白，知道的告诉下。
解决2
既然self被引用。我可以换个别的对象啊。让timer调用别的对象的timeAction，那么跟self就没半毛钱关系了。循环引用就迎刃而解了。写了个YBTimer。上代码吧
//
// YBTimer.h
// xxx
//
// Created by wyb on 2017/4/11.
// Copyright © 2017年 xxx. All rights reserved.
//
#import <Foundation/Foundation.h>
typedef void (^YBTimerBlock)(id userInfo);
@interface YBTimer : NSObject
+ (NSTimer *) scheduledTimerWithTimeInterval:(NSTimeInterval)interval
target:(id)aTarget
selector:(SEL)aSelector
userInfo:(id)userInfo
repeats:(BOOL)repeats;
+ (NSTimer *)scheduledTimerWithTimeInterval:(NSTimeInterval)interval
block:(YBTimerBlock)block
userInfo:(id)userInfo
repeats:(BOOL)repeats;
@end
//
// YBTimer.m
// xxx
//
// Created by wyb on 2017/4/11.
// Copyright © 2017年 xxx. All rights reserved.
//
#import "YBTimer.h"
//------------------------------YBTimerTargetBegin-------------------------------------
@interface YBTimerTarget : NSObject
@property (nonatomic, weak) id target;
@property (nonatomic, assign) SEL selector;
@property (nonatomic, weak) NSTimer* timer;
@end
@implementation YBTimerTarget
- (void)timeAction:(NSTimer *)timer {
if(self.target) {
[self.target performSelector:self.selector withObject:timer.userInfo afterDelay:0.0f];
} else {
[self.timer invalidate];
}
}
@end
//------------------------------YBTimerTargetEnd-------------------------------------
@implementation YBTimer
+ (NSTimer *) scheduledTimerWithTimeInterval:(NSTimeInterval)interval
target:(id)aTarget
selector:(SEL)aSelector
userInfo:(id)userInfo
repeats:(BOOL)repeats {
YBTimerTarget* timerTarget = [[YBTimerTarget alloc] init];
timerTarget.target = aTarget;
timerTarget.selector = aSelector;
timerTarget.timer = [NSTimer scheduledTimerWithTimeInterval:interval
target:timerTarget
selector:@selector(timeAction:)
userInfo:userInfo
repeats:repeats];
return timerTarget.timer;
}
+ (NSTimer *)scheduledTimerWithTimeInterval:(NSTimeInterval)interval
block:(YBTimerBlock)block
userInfo:(id)userInfo
repeats:(BOOL)repeats {
NSMutableArray *userInfoArray = [NSMutableArray arrayWithObject:[block copy]];
if (userInfo != nil) {
[userInfoArray addObject:userInfo];
}
return [self scheduledTimerWithTimeInterval:interval
target:self
selector:@selector(timerBlock:)
userInfo:[userInfoArray copy]
repeats:repeats];
}
+ (void)timerBlock:(NSArray*)userInfo {
YBTimerBlock block = userInfo[0];
id info = nil;
if (userInfo.count == 2) {
info = userInfo[1];
}
if (block) {
block(info);
}
}
@end
NSTimer 进阶 http://www.jianshu.com/p/19aab8570ce3
