多线程几种常用方案

1.GCD 加载图片过程

#import "UIImageView+DispatchLoad.h"  

@implementation UIImageView (DispatchLoad)  

- (void) setImageFromUrl:(NSString*)urlString {  

    [self setImageFromUrl:urlString completion:NULL];  

}  

- (void) setImageFromUrl:(NSString*)urlString   

              completion:(void (^)(void))completion {  

      

    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{  

          

        NSLog(@"Starting: %@", urlString);  

        UIImage *avatarImage = nil;   

        NSURL *url = [NSURL URLWithString:urlString];  

        NSData *responseData = [NSData dataWithContentsOfURL:url];  

        avatarImage = [UIImage imageWithData:responseData];  

        NSLog(@"Finishing: %@", urlString);  

          

        if (avatarImage) {  

            dispatch_async(dispatch_get_main_queue(), ^{  

                self.image = avatarImage;  

            });  

            dispatch_async(dispatch_get_main_queue(), completion);  

        }  

        else {  

            NSLog(@"-- impossible download: %@", urlString);  

        }  

    });     

}  

@end  

2.1 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];

例：

//    NSThread *thread = [[NSThread alloc] initWithTarget:self selector:@selector(loadUserList) object:nil];

//      [thread start];

//   [NSThread detachNewThreadSelector:@selector(loadUserList) toTarget:self withObject:nil];

   

2.2参数的意义：

selector ：线程执行的方法，这个selector只能有一个参数，而且不能有返回值。

target  ：selector消息发送的对象

argument:传输给target的唯一参数，也可以是nil

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

2.3 PS:不显式创建线程的方法：

用NSObject的类方法  performSelectorInBackground:withObject: 创建一个线程：

[Obj performSelectorInBackground:@selector(doSomething) withObject:nil];  

2.4.2线程间通讯

线程下载完图片后怎么通知主线程更新界面呢？

[self performSelectorOnMainThread:@selector(updateUI:) withObject:image waitUntilDone:YES];

performSelectorOnMainThread是NSObject的方法，除了可以更新主线程的数据外，还可以更新其他线程的比如：
用：performSelector:onThread:withObject:waitUntilDone: 


3.利用  NSOperationQueue 线程存储
3.1 建立子类

NSOperationQueue * contactOperationQueue = [[NSOperationQueue alloc] init];

     [contactOperationQueue setMaxConcurrentOperationCount:1];

     DownLocalContact * downloadContact = [[DownLocalContact alloc] initWithDelegate:self];

    [downloadContact setCompletionBlock:^{

                NSLog(@"download and save Data sucess!");

    }];

     [downloadContact setQueuePriority:NSOperationQueuePriorityVeryLow];

      [contactOperationQueue  addOperation :downloadContact];    
3.2 直接引用

#import "ViewController.h"

#define kURL @" http://avatar.youkuaiyun.com/2/C/D/1_totogo2010.jpg"

@interface ViewController ()

@end

@implementation ViewController

- (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;

}