Objective-C中的callback之一

最新推荐文章于 2021-08-30 16:44:50 发布

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本文通过一个Objective-C(NSObject)的实例演示了如何使用NSTimer与NSRunLoop来实现每隔两秒更新并打印时间的功能。该示例还展示了NSDateFormatter的单例模式使用方法。

OC中的Callback有四种类型：

下面是第一种：NSRunloop

// BNRLogger.h

// TOCRunloopa

#import <Foundation/Foundation.h>

@interface BNRLogger : NSObject

@property (nonatomic) NSDate *lastTime;

- (NSString *)lastTimerString;

- (void)updateLastTimer:(NSTimer *)t;

@end

// BNRLogger.m

// TOCRunloopa

#import "BNRLogger.h"

@implementation BNRLogger

- (NSString *)lastTimerString{

static NSDateFormatter *dateFormatter = nil;

if(!dateFormatter) {

dateFormatter = [[NSDateFormatter alloc] init];

[dateFormatter setTimeStyle:NSDateFormatterMediumStyle];

[dateFormatter setDateStyle:NSDateFormatterMediumStyle];

NSLog(@"created dateFormatter");

}

return [dateFormatter stringFromDate:self.lastTime];

}

- (void)updateLastTimer:(NSTimer *)t {

NSDate *now = [NSDate date];

[self setLastTime:now];

NSLog(@"I want to see the timer here: ");

NSLog(@"Just set time to %@", self.lastTimerString);

}

@end

// main.m

// TOCRunloopa

#import <Foundation/Foundation.h>

#import "BNRLogger.h"

int main(int argc, const char * argv[]) {

@autoreleasepool {

// insert code here...

BNRLogger *logger = [[BNRLogger alloc] init];

__unused NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:2.0

target:logger

selector:@selector(updateLastTimer:)

userInfo:nil

repeats:YES];

[[NSRunLoop currentRunLoop] run];

}

return 0;

}

Result:

2018-03-13 23:06:48.385109+0800 TOCRunloopa[70235:4288894] I want to see the timer here:

2018-03-13 23:06:48.385832+0800 TOCRunloopa[70235:4288894] created dateFormatter

2018-03-13 23:06:48.388740+0800 TOCRunloopa[70235:4288894] Just set time to 2018年3月13日下午11:06:48

2018-03-13 23:06:50.389817+0800 TOCRunloopa[70235:4288894] I want to see the timer here:

2018-03-13 23:06:50.390015+0800 TOCRunloopa[70235:4288894] Just set time to 2018年3月13日下午11:06:50

2018-03-13 23:06:52.385937+0800 TOCRunloopa[70235:4288894] I want to see the timer here:

2018-03-13 23:06:52.386101+0800 TOCRunloopa[70235:4288894] Just set time to 2018年3月13日下午11:06:52

2018-03-13 23:06:54.389943+0800 TOCRunloopa[70235:4288894] I want to see the timer here:

2018-03-13 23:06:54.390161+0800 TOCRunloopa[70235:4288894] Just set time to 2018年3月13日下午11:06:54

2018-03-13 23:06:56.389912+0800 TOCRunloopa[70235:4288894] I want to see the timer here:

2018-03-13 23:06:56.390110+0800 TOCRunloopa[70235:4288894] Just set time to 2018年3月13日下午11:06:56

2018-03-13 23:06:58.385713+0800 TOCRunloopa[70235:4288894] I want to see the timer here:

2018-03-13 23:06:58.385988+0800 TOCRunloopa[70235:4288894] Just set time to 2018年3月13日下午11:06:58

2018-03-13 23:07:00.385853+0800 TOCRunloopa[70235:4288894] I want to see the timer here:

2018-03-13 23:07:00.386030+0800 TOCRunloopa[70235:4288894] Just set time to 2018年3月13日下午11:07:00

2018-03-13 23:07:02.386859+0800 TOCRunloopa[70235:4288894] I want to see the timer here:

2018-03-13 23:07:02.387024+0800 TOCRunloopa[70235:4288894] Just set time to 2018年3月13日下午11:07:02

2018-03-13 23:07:04.390148+0800 TOCRunloopa[70235:4288894] I want to see the timer here:

2018-03-13 23:07:04.390356+0800 TOCRunloopa[70235:4288894] Just set time to 2018年3月13日下午11:07:04

2018-03-13 23:07:06.390241+0800 TOCRunloopa[70235:4288894] I want to see the timer here:

2018-03-13 23:07:06.390478+0800 TOCRunloopa[70235:4288894] Just set time to 2018年3月13日下午11:07:06-

-------------------------------持续每2秒输出一次