iOS让App后台运行方法小结

一般App进入后台之后，超过了后台运行时间，便进入了挂起状态，无法执行代码，但是内存并没有清除。
主要用到2个方法：
beginBackgroundTaskWithExpirationHandler://申请后台，该方法只有在App处于激活时调用才有效。 endBackgroundTask://注销后台
后台执行3分钟方法：

#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;
}

@endAppDelegate.m文件
#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
ViewController.m文件
#import "ViewController.h"
#import

@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

无限后台的方法，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。
好了，看方法！
先在info.plist文件里添加如此一条记录：