iOS-UIImageView加载网络下载的图片(异步+多线程)

//最原始加载网络图片方法，相当阻塞主线程，界面卡顿
-(void)setImageWithURL:(NSString *)imageDownloadUrl{
UIImageView *imageView = [[UIImageView alloc] initWithFrame:CGRectMake(44, 64, 250, 250)];
NSURL *URL = [NSURL URLWithString:imageDownloadUrl];
NSError *ERROR;
NSData *imageData = [NSData dataWithContentsOfURL:URL options:NSDataReadingMappedIfSafe error:&ERROR];
UIImage *image = [UIImage imageWithData:imageData];
[imageView setImage:image];
}

//异步线程加载网络下载图片 ——> 回到主线程更新UI
-(void)downloadImageWithUrl:(NSString *)imageDownloadURLStr{
//以便在block中使用
__block UIImage *image = [[UIImage alloc] init];
//图片下载链接
NSURL *imageDownloadURL = [NSURL URLWithString:imageDownloadURLStr];

//将图片下载在异步线程进行
//创建异步线程执行队列
dispatch_queue_t asynchronousQueue = dispatch_queue_create("imageDownloadQueue", NULL);
//创建异步线程
dispatch_async(asynchronousQueue, ^{
//网络下载图片  NSData格式
NSError *error;
NSData *imageData = [NSData dataWithContentsOfURL:imageDownloadURL options:NSDataReadingMappedIfSafe error:&error];
if (imageData) {
image = [UIImage imageWithData:imageData];
}
//回到主线程更新UI
dispatch_async(dispatch_get_main_queue(), ^{
[_imageView setImage:image];
});
});
}

#pragma mark - 下载图片-子线程调用
-(void)downloadImage{

/**
子线程里面的runloop默认不开启，也就意味着不会自动创建自动释放池，子线程里面autorelease的对象 就会没有池子释放。也就一位置偶棉没有办法进行释放造成内存泄露
所以需要手动创建

*/

@autoreleasepool {

NSLog(@"%@",[NSThread currentThread]);

NSURL *url = [NSURL URLWithString:@"http://baidu.com/image/Users/qiuxuewei/Desktop/qiu.JPG"];

NSData *data = [NSData dataWithContentsOfURL:url];

UIImage *image0 = [UIImage imageWithData:data];

UIImage *image = [UIImage imageNamed:@"qiu.JPG"];

//UI要求在主线程中进行
//self.imageView.image = image;

//1、 [self performSelectorOnMainThread:@selector(updataImage:) withObject:image waitUntilDone:NO];
//2、 [self performSelector:@selector(updataImage:) onThread:[NSThread mainThread] withObject:image waitUntilDone:YES];
[self.imageView performSelectorOnMainThread:@selector(updataImage:) withObject:image waitUntilDone:YES];

//waitUntilDone:  表示是否等待子线程方法执行完毕
//如果是YES:那就等子线程方法执行完再执行当前函数
NSLog(@"完成..");
}
}

-(void)updataImage:(UIImage *)image{

self.imageView.image = image;

}