NSOperation 依賴關系，就像你和女友，互相需要對方一樣。非常有意思。

 

#import "ViewController.h"

 

@interface ViewController ()

 

@end

 

@implementation ViewController

 

- (void)viewDidLoad {

[super viewDidLoad];

 

 

//操作依賴

//處理圖片的耗時操作在子線程中執行

NSBlockOperation *blockOp = [NSBlockOperation blockOperationWithBlock:^{

 

NSLog(@"blockOp 下載圖片 thread = %@",[NSThread currentThread]);

 

}];

 

NSBlockOperation *blockOp1 = [NSBlockOperation blockOperationWithBlock:^{

NSLog(@"blockOp1 給圖片添加水印 thread = %@",[NSThread currentThread]);

}];

 

 

NSBlockOperation *blockOp2 = [NSBlockOperation blockOperationWithBlock:^{

[NSThread sleepForTimeInterval:2.0];

 

NSLog(@"blockOp2 保存圖片 thread = %@",[NSThread currentThread]);

}];

 

 

//給blockOp1添加依賴關系，使blockOp1在blcokOp執行結束後執行

[blockOp1 addDependency:blockOp];//也就是下載結束之後再給圖片添加水印，然後保存圖片。一種依賴關系

[blockOp2 addDependency:blockOp1];

 

//創建隊列（把上面要干的事情丟到隊列中同時執行－－有點類似GCD中的異步，並發，開啟了多個線程）

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

//添加到隊列

[queue addOperation:blockOp];

[queue addOperation:blockOp1];

[queue addOperation:blockOp2];

 

//設置隊列中操作同時執行的最大數目，也就是說當前隊列中呢最多由幾個線程在同時執行，一般情況下允許最大的並發數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的操作依賴關系必須在主線程中執行

NSBlockOperation *blocOpMain = [NSBlockOperation blockOperationWithBlock:^{

NSLog(@"blockOpMain 刷新UI 顯示圖片,thread = %@",[NSThread currentThread]);

}];

 

//這兩個操作的依賴關系，跨隊列

[blocOpMain addDependency:blockOp2];

 

//主隊列

[[NSOperationQueue mainQueue]addOperation:blocOpMain];

 

}

 

@end