NSThread 有两种直接创建方式：
- (id)initWithTarget:(id)target selector:(SEL)selector object:(id)argument
+ (void)detachNewThreadSelector:(SEL)aSelector toTarget:(id)aTarget withObject:(id)anArgument
第一个是实例方法，第二个是类方法
1、[NSThread detachNewThreadSelector:@selector(doSomething:) toTarget:self withObject:nil];
2、NSThread* myThread = [[NSThread alloc] initWithTarget:self selector:@selector(doSomething:) object:nil];
[myThread start];
第一种方式会直接创建线程并且开始运行线程，第二种方式是先创建线程对象，然后再运行线程操作，在运行线程操作前可以设置线程的优先级等线程信息
下载图片的例子：
//
// ViewController.m
// NSThreadDemo
//
// Created by rongfzh on 12-9-23.
// Copyright (c) 2012年 rongfzh. All rights reserved.
//
#import "ViewController.h"
#define kURL @"http://avatar.csdn.net/2/C/D/1_totogo2010.jpg"
@interface ViewController ()
@end
@implementation ViewController
-(void)downloadImage:(NSString *) url{
NSData *data = [[NSData alloc] initWithContentsOfURL:[NSURL URLWithString:url]];
UIImage *image = [[UIImage alloc]initWithData:data];
if(image == nil){
}else{
[self performSelectorOnMainThread:@selector(updateUI:) withObject:image waitUntilDone:YES];
}
}
-(void)updateUI:(UIImage*) image{
self.imageView.image = image;
}
- (void)viewDidLoad
{
[super viewDidLoad];
// [NSThread detachNewThreadSelector:@selector(downloadImage:) toTarget:self withObject:kURL];
NSThread *thread = [[NSThread alloc]initWithTarget:self selector:@selector(downloadImage:) object:kURL];
[thread start];
}
@end
一种是用定义好的两个子类：
NSInvocationOperation 和 NSBlockOperation。
另一种是继承NSOperation
如果你也熟悉Java，NSOperation就和java.lang.Runnable接口很相似。和Java的Runnable一样，NSOperation也是设计用来扩展的，只需继承重写NSOperation的一个方法main。相当与java 中Runnalbe的Run方法。然后把NSOperation子类的对象放入NSOperationQueue队列中，该队列就会启动并开始处理它。
#import "ViewController.h"
#define kURL @"http://avatar.csdn.net/2/C/D/1_totogo2010.jpg"
- (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;
}
@end
dispatch queue分为下面三种： Serial
又称为private dispatch queues，同时只执行一个任务。Serial queue通常用于同步访问特定的资源或数据。当你创建多个Serial queue时，虽然它们各自是同步执行的，但Serial queue与Serial queue之间是并发执行的。 Concurrent
又称为global dispatch queue，可以并发地执行多个任务，但是执行完成的顺序是随机的。 Main dispatch queue
它是全局可用的serial queue，它是在应用程序主线程上执行任务的。
为了避免界面在处理耗时的操作时卡死，比如读取网络数据，IO,数据库读写等，我们会在另外一个线程中处理这些操作，然后通知主线程更新界面。
用GCD实现这个流程的操作比前面介绍的NSThread NSOperation的方法都要简单。代码框架结构如下：
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
});
});
如果这样还不清晰的话，那我们还是用上两篇博客中的下载图片为例子，代码如下：
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
NSURL * url = [NSURL URLWithString:@"http://avatar.csdn.net/2/C/D/1_totogo2010.jpg"];
NSData * data = [[NSData alloc]initWithContentsOfURL:url];
UIImage *image = [[UIImage alloc]initWithData:data];
if (data != nil) {
dispatch_async(dispatch_get_main_queue(), ^{
self.imageView.image = image;
});
}
});
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。这个方法很有用，比如你执行三个下载任务，当三个任务都下载完成后你才通知界面说完成的了。下面是一段例子代码：
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);
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
例子代码如下：
```
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");
}); ```
执行某个代码片段N次。
dispatch_apply(5, globalQ, ^(size_t index) {
// 执行5次
});
@interface NSObject (NSThreadPerformAdditions)
- (void)performSelectorOnMainThread:(SEL)aSelector withObject:(id)arg waitUntilDone:(BOOL)wait modes:(NSArray *)array;
- (void)performSelectorOnMainThread:(SEL)aSelector withObject:(id)arg waitUntilDone:(BOOL)wait;
// equivalent to the first method with kCFRunLoopCommonModes
- (void)performSelector:(SEL)aSelector onThread:(NSThread *)thr withObject:(id)arg waitUntilDone:(BOOL)wait modes:(NSArray *)array NS_AVAILABLE(10_5, 2_0);
- (void)performSelector:(SEL)aSelector onThread:(NSThread *)thr withObject:(id)arg waitUntilDone:(BOOL)wait NS_AVAILABLE(10_5, 2_0);
// equivalent to the first method with kCFRunLoopCommonModes
- (void)performSelectorInBackground:(SEL)aSelector withObject:(id)arg NS_AVAILABLE(10_5, 2_0);
@end