NSOperation使用系统提供子类的方法--处理复杂任务

//创建一个队列
NSOperationQueue *operation=[[NSOperationQueue alloc]init];
//把任务放在NSBlockOperation里面
NSBlockOperation *myOperation=[NSBlockOperation blockOperationWithBlock:^{
NSData *firstData=[NSData dataWithContentsOfURL:[NSURL URLWithString:KURL1]];

dispatch_async(dispatch_get_main_queue(), ^{

_firstImageView.image=[UIImage imageWithData:firstData];
});

}];

//把第二任务添加到操作队列
[myOperation addExecutionBlock:^{
NSData *secondData=[NSData dataWithContentsOfURL:[NSURL URLWithString:KURL1]];

dispatch_async(dispatch_get_main_queue(), ^{

_secondImageView.image=[UIImage imageWithData:secondData];
});

}];
[operation addOperation:myOperation];