实现多线程的方式一般有三种：NSThread、GCD、NSOperation
1、NSThread：适用简单,简单易用，可以直接操作线程，oc 的，偶尔使用，程序员管理生命周期
//1.1 创建线程
//实例方法：创建线程后需手动开启线程
- (id)initWithTarget:(id)target selector:(SEL)selector object:(id)argument；
//demo
NSThread* myThread = [[NSThread alloc] initWithTarget:self
selector:@selector(doSomething:)
object:nil];
[myThread start];
//类方法：创建完成后直接运行线程
+ (void)detachNewThreadSelector:(SEL)aSelector toTarget:(id)aTarget withObject:(id)anArgument；
//demo
[NSThread detachNewThreadSelector:@selector(doSomething:) toTarget:self withObject:nil];
//通知主线程更新UI
[self performSelectorOnMainThread:@selector(updateUI:) withObject:image waitUntilDone:YES];
//1.2 锁
NSLock *theLock = [[NSLock alloc] init];
//上锁
[theLock lock];
//解锁
[theLock unlock];
2、GCD：替代 NSThread 等多线程技术，充分利用设备多核技术，c的，经常使用，系统自动管理线程生命周期
//1、常用的方法dispatch_async
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
// 耗时的操作
dispatch_async(dispatch_get_main_queue(), ^{
// 更新界面
});
});
//2、dispatch_group_async的使用
//dispatch_group_async可以实现监听一组任务是否完成，完成后得到通知执行其他的操作。
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_group_t group = dispatch_group_create();
dispatch_group_async(group, queue, ^{
[NSThread sleepForTimeInterval:1];
NSLog(@"group1");
});
dispatch_group_async(group, queue, ^{
[NSThread sleepForTimeInterval:2];
NSLog(@"group2");
});
dispatch_group_async(group, queue, ^{
[NSThread sleepForTimeInterval:3];
NSLog(@"group3");
});
dispatch_group_notify(group, dispatch_get_main_queue(), ^{
NSLog(@"updateUi");
});
dispatch_release(group);
//当三个线程都完成之后，group才会执行
dispatch_group_notify(group, dispatch_get_main_queue(), ^{
});
//中的方法
//3、dispatch_barrier_async的使用
//dispatch_barrier_async是在前面的任务执行结束后它才执行，而且它后面的任务等它执行完成之后才会执行
//demo
dispatch_queue_t queue = dispatch_queue_create("gcdtest.rongfzh.yc", DISPATCH_QUEUE_CONCURRENT);
dispatch_async(queue, ^{
[NSThread sleepForTimeInterval:2];
NSLog(@"dispatch_async1");
});
dispatch_async(queue, ^{
[NSThread sleepForTimeInterval:4];
NSLog(@"dispatch_async2");
});
dispatch_barrier_async(queue, ^{
NSLog(@"dispatch_barrier_async");
[NSThread sleepForTimeInterval:4];
});
dispatch_async(queue, ^{
[NSThread sleepForTimeInterval:1];
NSLog(@"dispatch_async3");
});
//运行结果
//dispatch_async1
//dispatch_async2
//dispatch_barrier_async
//dispatch_async3
//4、dispatch_apply 使用
重复执行同一段代码。
dispatch_apply(5, globalQ, ^(size_t index) {
// 执行5次
});
3、NSOperation：基于 gcd 的封装，比 gcd 简单，更加面向对象，系统自动管理线程生命周期，经常使用
- (void)viewDidLoad
{
[super viewDidLoad];
NSInvocationOperation *operation = [[NSInvocationOperation alloc]initWithTarget:self selector:@selector(downloadImage:) object:kURL];
NSOperationQueue *queue = [[NSOperationQueue alloc]init];
[queue addOperation:operation];
// Do any additional setup after loading the view, typically from a nib.
}
-(void)downloadImage:(NSString *)url{
NSLog(@"url:%@", url);
NSURL *nsUrl = [NSURL URLWithString:url];
NSData *data = [[NSData alloc]initWithContentsOfURL:nsUrl];
UIImage * image = [[UIImage alloc]initWithData:data];
[self performSelectorOnMainThread:@selector(updateUI:) withObject:image waitUntilDone:YES];
}
-(void)updateUI:(UIImage*) image{
self.imageView.image = image;
}
//n建一个NSInvocationOperatio线程，并且放到NSOperationQueue中。后台线程执行downloadImage方法。方法完成后用performSelectorOnMainThread执行主线程updateUI方法。
//加入到NSOperationQueue的线程默认全部同时进行。若想做限制，可用此方法
[queue setMaxConcurrentOperationCount:5];
//默认为-1，即无限制
