1.开启线程的方法一

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

2.开启线程的方法二 

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

3.开启线程的方法三

    [self performSelectorInBackground:@selector(_update) withObject:nil];

4.开启线程的方法四

    NSOperationQueue *queue=[[NSOperationQueue alloc] init];
    [queue addOperationWithBlock:^{
        for(int i=0;i<50;i++){
            PRintf("子线程\n");
        }
    }];

5.开启线程的方法五

    //第一步开启线程池
        NSOperationQueue * queue=[[NSOperationQueue alloc] init];
    //设置并发数目
    [queue setMaxConcurrentOperationCount:2];
    
    //第二部创建多线程添加到线程池
    NSInvocationOperation * thread1=[[NSInvocationOperation alloc] initWithTarget:self selector:@selector(_update1) object:nil];
    NSInvocationOperation *thread2=[[NSInvocationOperation alloc] initWithTarget:self selector:@selector(_update2) object:nil];
    
    [thread1 setQueuePriority:NSOperationQueuePriorityVeryLow];
    [thread2 setQueuePriority:NSOperationQueuePriorityVeryHigh];
    
    [queue addOperation:thread1];
    [queue addOperation:thread2];

1.核心思想

　　考虑到如果加载网络图片会延迟，在一个主线程加载会影响控件的渲染，此时可以采取多线程，异步加载完成后刷新UI。

2.实现思路

　　通过为UIImageView 增加类目来实现多线程下载。

　　主要代码：

#import "UIImageView+thread.h"

@implementation UIImageView(load)


- (void) setImageWithUrl:(NSString *)url{
    [self performSelectorInBackground:@selector(_loadImage:) withObject:url];


}


- (void) _loadImage:(NSString *)u{

    @autoreleasepool {
        
        NSURL *url=[NSURL URLWithString:u];
        NSData *data=[NSData dataWithContentsOfURL:url];

        UIImage *image=[UIImage imageWithData:data];
        
        [self performSelectorOnMainThread:@selector(setImage:) withObject:image waitUntilDone:NO];
        
    }
}