前言
我们一般做的短信验证码功能，应用在前台运行的时候，肯定是没有问题的，但是点击一下Home键进入后台挂起的状态，我们的定时器就停止了。
网上很多说记录什么进入后台的时间，我觉的那太费事了，我们完全可以通过申请应用在后台执行来执行我们的倒计时。
1、先放我们倒计时的代码，这段代码在模拟器运行是没有问题的，但是在真机进入挂起状态会停止
<pre>
-
(void)sentPhoneCodeTimeMethod {
//倒计时时间 - 60S
__block NSInteger timeOut = 59;
//执行队列
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
//计时器 -》 dispatch_source_set_timer自动生成
dispatch_source_t timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue);
dispatch_source_set_timer(timer, DISPATCH_TIME_NOW, 1.0 * NSEC_PER_SEC, 0 * NSEC_PER_SEC);dispatch_source_set_event_handler(timer, ^{
if (timeOut <= 0) {
dispatch_source_cancel(timer);
//主线程设置按钮样式
dispatch_async(dispatch_get_main_queue(), ^{
// 倒计时结束
[self.captchaButton setBackgroundImage:kImage(kCaptchaButtonNormal) forState:UIControlStateNormal];
[self.captchaButton setTitle:kCaptchaButtonTitle forState:UIControlStateNormal];
[self.captchaButton setEnabled:YES];[self.captchaButton setUserInteractionEnabled:YES]; }); } else { //开始计时 //剩余秒数 seconds NSInteger seconds = timeOut % 60; NSString *strTime = [NSString stringWithFormat:@"%.1ld", seconds]; //主线程设置按钮样式 dispatch_async(dispatch_get_main_queue(), ^{ [UIView beginAnimations:nil context:nil]; [UIView setAnimationDuration:1.0]; [self.captchaButton setBackgroundImage:kImage(kCaptchaButtonSelected) forState:UIControlStateNormal]; NSString *title = [NSString stringWithFormat:@"%@ s",strTime]; [self.captchaButton setTitle:title forState:UIControlStateNormal]; [UIView commitAnimations]; //计时器件不允许点击 [self.captchaButton setUserInteractionEnabled:NO]; }); timeOut--; }});
dispatch_resume(timer);
}
</pre>
2、下面是我们用到的一个小技巧
一般来说，如果不进行后台申请，在iOS系统上，当应用退到后台后，只有5s的时间去执行代码，之后将进入挂起状态。只有像音频播放、定位、newsstand、VoIP等功能才能持续在后台运行。但是开发其它应用是我们可以通过申请后台，来获得3分钟的后台执行代码时间（iOS7以前是10分钟）。
所以我们决定申请3分钟来执行我们1分钟的倒计时代码：
<pre>
import "AppDelegate.h"
@interface AppDelegate (){
NSInteger count;
}
@property(strong, nonatomic)NSTimer *mTimer;
@property(assign, nonatomic)UIBackgroundTaskIdentifier backIden;
@end
@implementation AppDelegate
-
(BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
// Override point for customization after application launch.count=0;
return YES;
} (void)applicationDidEnterBackground:(UIApplication *)application {
_mTimer = [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(countAction) userInfo:nil repeats:YES];
[[NSRunLoop currentRunLoop] addTimer:_mTimer forMode:NSRunLoopCommonModes];
[self beginTask];
}(void)applicationWillEnterForeground:(UIApplication *)application {
NSLog(@"进入前台");
[self endBack];
}
//计时
-(void)countAction{
NSLog(@"%li",count++);
}
//申请后台
-(void)beginTask
{
NSLog(@"begin=============");
_backIden = [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:^{
//在时间到之前会进入这个block，一般是iOS7及以上是3分钟。按照规范，在这里要手动结束后台，你不写也是会结束的（据说会crash）
NSLog(@"将要挂起=============");
[self endBack];
}];
}
//注销后台
-(void)endBack
{
NSLog(@"end=============");
[[UIApplication sharedApplication] endBackgroundTask:_backIden];
_backIden = UIBackgroundTaskInvalid;
}
@end
</pre>
这样就轻松、完美解决了我们的需求了！！！
3、 扩充无限倒计时
慎用！因为这个需要申请后台播放音频的权限。如果你的应用不是相关应用，AppStore审核可能不会通过。
先在我们的info.plist文件配置中，添加一行，如下两个属性：
Required background modes
App plays audio or streams audio/video using AirPlay
AppDelegate.m文件中代码还是和上面一样，设置 UIBackgroundTaskIdentifier
<pre>
import "AppDelegate.h"
@interface AppDelegate (){
NSInteger count;
}
@property(strong, nonatomic)NSTimer *mTimer;
@property(assign, nonatomic)UIBackgroundTaskIdentifier backIden;
@end
@implementation AppDelegate
-
(BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
// Override point for customization after application launch.count=0;
return YES;
} (void)applicationDidEnterBackground:(UIApplication *)application {
_mTimer = [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(countAction) userInfo:nil repeats:YES];
[[NSRunLoop currentRunLoop] addTimer:_mTimer forMode:NSRunLoopCommonModes];
[self beginTask];
}(void)applicationWillEnterForeground:(UIApplication *)application {
NSLog(@"进入前台");
[self endBack];
}
//计时
-(void)countAction{
NSLog(@"%li",count++);
}
//申请后台
-(void)beginTask
{
NSLog(@"begin=============");
_backIden = [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:^{
NSLog(@"将要挂起=============");
[self endBack];
}];
}
//注销后台
-(void)endBack
{
NSLog(@"end=============");
[[UIApplication sharedApplication] endBackgroundTask:_backIden];
_backIden = UIBackgroundTaskInvalid;
}
@end
</pre>
在我们需要后台运行的控制器中，例如ViewController.m
<pre>
import "ViewController.h"
import <AVFoundation/AVFoundation.h>
@interface ViewController ()
@property(strong, nonatomic)AVAudioPlayer *mPlayer;
@property(assign, nonatomic)CGFloat mCount;
@end
@implementation ViewController
-
(void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib._mCount = 0;
NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:10 target:self selector:@selector(countTime) userInfo:nil repeats:YES];
[[NSRunLoop currentRunLoop] addTimer:timer forMode:NSRunLoopCommonModes];
}
-(void)countTime{
_mCount+=10;
NSLog(@"%f",_mCount);
if ([[UIApplication sharedApplication] backgroundTimeRemaining] < 60.) {//当剩余时间小于60时，开如播放音乐，并用这个假前台状态再次申请后台
NSLog(@"播放%@",[NSThread currentThread]);
[self playMusic];
//申请后台
[[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:^{
NSLog(@"我要挂起了");
}];
}
}
-(void)playMusic{
//1.音频文件的url路径，实际开发中，用无声音乐
NSURL *url=[[NSBundle mainBundle]URLForResource:@"欢沁.mp3" withExtension:Nil];
//2.创建播放器（注意：一个AVAudioPlayer只能播放一个url）
_mPlayer=[[AVAudioPlayer alloc]initWithContentsOfURL:url error:Nil];
//3.缓冲
[_mPlayer prepareToPlay];
//4.播放
[_mPlayer play];
}
@end
</pre>
完。
自助者，天助之。
