NSOperationQueue 设置依赖

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

NSBlockOperation*blockOperation=[NSBlockOperation blockOperationWithBlock:^{

NSURL *url = [NSURL URLWithString:@"http://img.pconline.com.cn/images/photoblog/9/9/8/1/9981681/200910/11/1255259355826.jpg"];

NSData*data=[NSData dataWithContentsOfURL:url];

[[NSOperationQueue mainQueue] addOperationWithBlock:^{

self.singleImageView.image=[UIImage imageWithData:data];

}];

}];

NSBlockOperation*blockOperation1=[NSBlockOperation blockOperationWithBlock:^{

NSURL *url = [NSURL URLWithString:@"http://img.pconline.com.cn/images/photoblog/9/9/8/1/9981681/200910/11/1255259355826.jpg"];

NSData*data=[NSData dataWithContentsOfURL:url];

[[NSOperationQueue mainQueue] addOperationWithBlock:^{

self.secondImageView.image=[UIImage imageWithData:data];

}];

}];

__weak __typeof__(self) weakSelf = self;

NSBlockOperation*blockOperation3=[NSBlockOperation blockOperationWithBlock:^{

UIGraphicsBeginImageContext(self.bottomImageView.frame.size);

CGSize size= self.bottomImageView.frame.size;

[weakSelf.singleImageView.image drawInRect:CGRectMake(0,size.width/2,size.height)];

[weakSelf.secondImageView.image drawInRect:CGRectMake(size.width/2,size.height)];

UIImage *finalImage=UIGraphicsGetImageFromCurrentImageContext();

[[NSOperationQueue mainQueue] addOperationWithBlock:^{

weakSelf.bottomImageView.image=finalImage;

}];

UIGraphicsEndImageContext();

}];

[blockOperation3 addDependency:blockOperation1];

[blockOperation3 addDependency:blockOperation];

[queue addOperation:blockOperation3];

[queue addOperation:blockOperation1];

[queue addOperation:blockOperation];

（编辑：李大同）

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