NSOperation 依赖关系，就像你和女友，互相需要对方一样。非常有意思。
#import "ViewController.h"
@interface ViewController ()
@end
@implementation ViewController
- (void)viewDidLoad {
[super
viewDidLoad];
//操作依赖
//处理图片的耗时操作在子线程中执行
NSBlockOperation *blockOp = [NSBlockOperation
blockOperationWithBlock:^{
NSLog(@"blockOp
下载图片 thread = %@",[NSThread
currentThread]);
}];
NSBlockOperation *blockOp1 = [NSBlockOperation
blockOperationWithBlock:^{
NSLog(@"blockOp1
给图片添加水印 thread = %@",[NSThread
currentThread]);
}];
NSBlockOperation *blockOp2 = [NSBlockOperation
blockOperationWithBlock:^{
[NSThread
sleepForTimeInterval:2.0];
NSLog(@"blockOp2
保存图片 thread = %@",[NSThread
currentThread]);
}];
//给blockOp1添加依赖关系，使blockOp1在blcokOp执行结束后执行
[blockOp1 addDependency:blockOp];//也就是下载结束之后再给图片添加水印，然后保存图片。一种依赖关系
[blockOp2 addDependency:blockOp1];
//创建队列（把上面要干的事情丢到队列中同时执行－－有点类似GCD中的异步，并发，开启了多个线程）
NSOperationQueue *queue = [[NSOperationQueue
alloc]init];
//添加到队列
[queue addOperation:blockOp];
[queue addOperation:blockOp1];
[queue addOperation:blockOp2];
//设置队列中操作同时执行的最大数目，也就是说当前队列中呢最多由几个线程在同时执行，一般情况下允许最大的并发数2或者3
[queue setMaxConcurrentOperationCount:3];
//
for (int i =
0; i<50; i++) {
NSBlockOperation *blockOpp = [NSBlockOperation
blockOperationWithBlock:^{
NSLog(@"blockOpp i = %d thread = %@",i,[NSThread
currentThread]);
}];
[queue addOperation:blockOpp];
}
//刷新UI的操作依赖关系必须在主线程中执行
NSBlockOperation *blocOpMain = [NSBlockOperation
blockOperationWithBlock:^{
NSLog(@"blockOpMain
刷新UI 显示图片,thread = %@",[NSThread
currentThread]);
}];
//这两个操作的依赖关系，跨队列
[blocOpMain addDependency:blockOp2];
//主队列
[[NSOperationQueue
mainQueue]addOperation:blocOpMain];
}
@end