NSTimer的基础用法以及程序挂起后NSTimer仍然可以在后台运行计时

1. 关于NSTimer一些基本的知识，网上应该有很多讲解，废话不多少，直接上代码

(1) 下面是简单的实现代码

#import "NSTimerController.h"

#define SCREEN_WIDTH [UIScreen mainScreen].bounds.size.width
#define SCREEN_HEIGHT [UIScreen mainScreen].bounds.size.height
static const NSInteger button_tag = 100;

@interface NSTimerController ()

@property (nonatomic,strong) NSTimer* timer; /*定时器*/
@property (nonatomic,assign) NSInteger secondsCountDown; /*倒计时的时间数*/
@property (nonatomic,strong) UIButton* count_button; /*点击的按钮*/
@property (nonatomic,assign) NSInteger space; /*宽度*/
@property (nonatomic,assign) BOOL isClick; /*防止连续点击*/

@end

@implementation NSTimerController

- (void)viewDidLoad
{
    [super viewDidLoad];
    _secondsCountDown = 20; /*初使时间20秒*/
    _space = 300; /*按钮的宽度*/
    [self count_button];
}

-(void) viewWillDisappear:(BOOL)animated
{
    [super viewWillDisappear:animated];
    [_timer invalidate]; /*将定时器从运行循环中移除*/
    _timer = nil; /*销毁定时器, 这样可以避免控制器不死*/
}

-(UIButton*) count_button
{
    if (!_count_button)
    {
        _count_button = [UIButton buttonWithType:UIButtonTypeCustom];
        [self.view addSubview:_count_button];
        _count_button.frame = CGRectMake(SCREEN_WIDTH / 2 - 150, SCREEN_HEIGHT - 300, _space, 40);
        _count_button.tag = button_tag;
        _count_button.layer.cornerRadius = 5;
        [_count_button setTitle:@"重新获取" forState:UIControlStateNormal];
        _count_button.backgroundColor = [UIColor orangeColor];
        [_count_button setTitleColor:[UIColor whiteColor] forState:UIControlStateNormal];
        [_count_button addTarget:self action:@selector(buttonAction:) forControlEvents:UIControlEventTouchUpInside];
    }
    return _count_button;
}

-(void) buttonAction:(UIButton*) sender
{
    if (!_isClick)
    {
        _timer = [NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(timeFireMethod) userInfo:nil repeats:YES];

        /*注意点：
         将计数器的repeats设置为YES的时候，self的引用计数会加1。
         因此可能会导致self（即viewController）不能release。
         所以，必须在viewWillAppear的时候，将计数器timer停止，否则可能会导致内存泄露。*/
        
        /*手动启动Runloop,然后使其在线程池里运行*/
        /* 
         1: 下面这个方法切忌不要轻易使用，避免网络请求的线程会被杀死：[[NSRunLoop currentRunLoop] run];

         2: 如果想用，建议如下操作：
         // dispatch_async(dispatch_get_global_queue(0, 0), ^{
         //  _countDownTimer = [NSTimer  scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(timeFireMethod) userInfo:nil repeats:YES];
         // [[NSRunLoop currentRunLoop] run];
                    });
          */

        //正确用法：
         [[NSRunLoop currentRunLoop] addTimer:_timer  forMode:NSRunLoopCommonModes];
    }
}

-(void) timeFireMethod
{
    _isClick = YES;
    _secondsCountDown--;
    [_count_button setTitle:[NSString stringWithFormat:@"重新获取 (%ld)",(long)_secondsCountDown] forState:UIControlStateNormal];
    [_count_button setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
    NSLog(@"_secondsCountDown:%ld",(long)_secondsCountDown);
    if (_secondsCountDown <= 0)
    {
        _isClick = NO;
        [_timer invalidate];
        _secondsCountDown = 20;
        [_count_button setTitle:@"重新获取" forState:UIControlStateNormal];
        [_count_button setTitleColor:[UIColor whiteColor] forState:UIControlStateNormal];
    }
}

@end

下面两张图是简易的效果图：

图1.png

图2.png

(2) 上面的代码中，有关于一些细节的说明，但是还有一些其他的重点细节，在下面说下

在页面即将消失的时候关闭定时器，之后等页面再次打开的时候,又开启定时器(只要是防止它在后台运行，暂用CPU)

-(void) viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];
    /*开启继续运行NSTimer*/
    [_timer setFireDate:[NSDate distantPast]];
}

-(void) viewWillDisappear:(BOOL)animated
{
    [super viewWillDisappear:animated];
    /*关闭NSTimer*/
    [_timer setFireDate:[NSDate distantFuture]];
}

2. 程序挂起后NSTimer仍然可以在后台运行计时

具体操作如下:

步骤一： 在info里面如下设置：
info -->添加 Required background modes -->设置 App plays audio or streams audio/video using AirPlay

3C1F3F3C-6860-4A29-84C1-65554EFDF687.png

步骤二：在AppDelegate.m里面调用

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    
    /*定时器后台运行*/
    NSError *setCategoryErr = nil;
    NSError *activationErr  = nil;
    /*设置Audio Session的Category 一般会在激活之前设置好Category和mode。但是也可以在已激活的audio session中设置，不过会在发生route change之后才会发生改变*/
    [[AVAudioSession sharedInstance] setCategory: AVAudioSessionCategoryPlayback error: &setCategoryErr];
    /*激活Audio Session*/
    [[AVAudioSession sharedInstance] setActive: YES error: &activationErr];
 }

/*
 通过UIBackgroundTaskIdentifier可以实现有限时间内在后台运行程序
 程序进入后台时调用applicationDidEnterBackground函数，
 */
- (void)applicationDidEnterBackground:(UIApplication *)application{
    
    UIApplication* app = [UIApplication sharedApplication];
    __block UIBackgroundTaskIdentifier bgTask;
    
    /*注册一个后台任务，告诉系统我们需要向系统借一些事件*/
    bgTask = [app beginBackgroundTaskWithExpirationHandler:^{
        dispatch_async(dispatch_get_main_queue(), ^{
            if (bgTask != UIBackgroundTaskInvalid)
            {
                /*销毁后台任务标识符*/
                /*不管有没有完成，结束background_task任务*/
                bgTask = UIBackgroundTaskInvalid;
            }
        });
    }];
    
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        dispatch_async(dispatch_get_main_queue(), ^{
            if (bgTask != UIBackgroundTaskInvalid)
            {
                /*销毁后台任务标识符*/
                /*不管有没有完成，结束background_task任务*/
                bgTask = UIBackgroundTaskInvalid;
            }
        });
    });
}

参考如下链接知识，深表感谢：

IOS音频播放学习参考
IOS后台挂起时运行程序UIBackgroundTaskIdentifier