> For the complete documentation index, see [llms.txt](https://awesome-tips.gitbook.io/ios/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://awesome-tips.gitbook.io/ios/duo-xian-cheng/content-7.md).

# 8. 说说 NSTimer 的新 API

**作者**: [halohily](https://weibo.com/halohily)

在以往的 `iOS` 版本中，我们为了避免 `NSTimer` 的循环引用问题，一个比较常用的解决办法是为 `NSTimer` 添加一个 `category`，新增传入 `block` 类型参数的接口。分类内部实现是将此 `block` 作为 `NSTimer` 的 `userInfo` 参数传入，而 `NSTimer` 的 `target` 则设置为 `timer` 自己。以此来避免 `NSTimer` 持有 `VC`。代码如下:

```
// NSTimer+BlocksSupport.h
#import <Foundation/Foundation.h>

@interface NSTimer (BlocksSupport)
+ (NSTimer *)ly_scheduledTimerWithTimeInterval:(NSTimeInterval)interval
repeats:(BOOL)repeats
block:(void(^)())block;
@end

// NSTimer+BlocksSupport.m
#import "NSTimer+BlocksSupport.h"

@implementation NSTimer (BlocksSupport)
+ (NSTimer *)ly_scheduledTimerWithTimeInterval:(NSTimeInterval)interval
repeats:(BOOL)repeats
block:(void(^)())block;
{
    return [self scheduledTimerWithTimeInterval:interval
                        target:self
                      selector:@selector(ly_blockInvoke:)
                      userInfo:[block copy]
                       repeats:repeats];
}

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

而在 `iOS 10` 之后，苹果终于为 `NSTimer` 添加了一个官方 `API`，支持传入 `block` 类型参数。可谓是千呼万唤始出来。新官方 `API` 包括：

```
+ (NSTimer *)timerWithTimeInterval:(NSTimeInterval)interval
repeats:(BOOL)repeats
block:(void (^)(NSTimer *timer))block API_AVAILABLE(macosx(10.12), ios(10.0), watchos(3.0), tvos(10.0));
+ (NSTimer *)scheduledTimerWithTimeInterval:(NSTimeInterval)interval
repeats:(BOOL)repeats
block:(void (^)(NSTimer *timer))block API_AVAILABLE(macosx(10.12), ios(10.0), watchos(3.0), tvos(10.0));
```