iOS多線程---NSOperation的常用操作
1.最大並發數：
- (NSInteger)maxConcurrentOperationCount;- (void)setMaxConcurrentOperationCount:(NSInteger)cnt;
NSOperationQueue *queue = [[NSOperationQueue alloc]init]; queue.maxConcurrentOperationCount = 3;
註：系統一般會根據內存大小自動設置並發數目，也可以自己設定，但是不要亂設，一般不要超過5個。 2.暫停和取消
（1）取消隊列的所有操作
- (void)cancelAllOperations;
提?:也可以調用NSOperation的- (void)cancel?法取消單個操作
（2）暫停和恢復隊列
- (void)setSuspended:(BOOL)b; // YES代表暫停隊列,NO代表恢復隊列
- (BOOL)isSuspended; //當前狀態
3.操作優先級 : 設置NSOPeration的優先級，可以改變在NSOPerationQueue中的執行優先級
[operation2 setQueuePriority:NSOperationQueuePriorityNormal]; //設置優先級 NSOperationQueuePriority priority= operation2.queuePriority; //獲去操作的優先級
4.操作依賴
有兩個操作，operationA:買飯和operationB:吃飯，必須要先買飯，然後再吃飯。操作B：吃飯 必須等到操作A：買飯 的操作完成後才能執行。這就是依賴關系。
在NSOPeration中描述依賴用：[operationB addDependency:operationA];
- (void)viewDidLoad { [super viewDidLoad]; NSInvocationOperation *operationA = [[NSInvocationOperation alloc]initWithTarget:self selector:@selector(testAction) object:nil]; NSInvocationOperation *operationB = [[NSInvocationOperation alloc]initWithTarget:self selector:@selector(testAction1) object:nil]; [operationB addDependency:operationA]; //定義隊列 NSOperationQueue *queue = [[NSOperationQueue alloc]init]; //將操作添加到隊列 [queue addOperation:operationA]; [queue addOperation:operationB]; } -(void)testAction { for (int i = 0; i < 5; i ++) { NSLog(@"給五個人買飯帶回宿舍----%@",[NSThread currentThread]); } } -(void)testAction1 { for (int i = 0; i < 5; i ++) { NSLog(@"五個人開始吃飯----%@",[NSThread currentThread]); } }
2017-06-18 11:33:26.765 demo[17639:3076261] 給五個人買飯帶回宿舍----<NSThread: 0x600000267b40>{number = 3, name = (null)}
2017-06-18 11:33:26.766 demo[17639:3076261] 給五個人買飯帶回宿舍----<NSThread: 0x600000267b40>{number = 3, name = (null)}
2017-06-18 11:33:26.767 demo[17639:3076261] 給五個人買飯帶回宿舍----<NSThread: 0x600000267b40>{number = 3, name = (null)}
2017-06-18 11:33:26.768 demo[17639:3076261] 給五個人買飯帶回宿舍----<NSThread: 0x600000267b40>{number = 3, name = (null)}
2017-06-18 11:33:26.769 demo[17639:3076261] 給五個人買飯帶回宿舍----<NSThread: 0x600000267b40>{number = 3, name = (null)}
2017-06-18 11:33:26.770 demo[17639:3076261] 五個人開始吃飯----<NSThread: 0x600000267b40>{number = 3, name = (null)}
2017-06-18 11:33:26.776 demo[17639:3076261] 五個人開始吃飯----<NSThread: 0x600000267b40>{number = 3, name = (null)}
2017-06-18 11:33:26.777 demo[17639:3076261] 五個人開始吃飯----<NSThread: 0x600000267b40>{number = 3, name = (null)}
2017-06-18 11:33:26.781 demo[17639:3076261] 五個人開始吃飯----<NSThread: 0x600000267b40>{number = 3, name = (null)}
2017-06-18 11:33:26.782 demo[17639:3076261] 五個人開始吃飯----<NSThread: 0x600000267b40>{number = 3, name = (null)}
註：用for循環更能看出操作的執行順序。
5.操作的監聽
有時候需要執行完一個操作再執行另個操作，可以將這兩個操作寫在一起，但是當代碼很多的時候，會造成閱讀性不強。
NSBlockOperation *operation = [NSBlockOperation blockOperationWithBlock:^{ for (int i = 0; i < 5; i ++) { NSLog(@"給五個人買飯帶回宿舍----%@",[NSThread currentThread]); } for (int i = 0; i < 5; i ++) { NSLog(@"五個人開始吃飯----%@",[NSThread currentThread]); } }]; //定義隊列 NSOperationQueue *queue = [[NSOperationQueue alloc]init]; //將操作添加到隊列 [queue addOperation:operation];
也可以分開寫：
NSBlockOperation *operation = [NSBlockOperation blockOperationWithBlock:^{ for (int i = 0; i < 5; i ++) { NSLog(@"給五個人買飯帶回宿舍----%@",[NSThread currentThread]); } }]; operation.completionBlock = ^{ for (int i = 0; i < 5; i ++) { NSLog(@"五個人開始吃飯----%@",[NSThread currentThread]); } }; //定義隊列 NSOperationQueue *queue = [[NSOperationQueue alloc]init]; //將操作添加到隊列 [queue addOperation:operation];
2017-06-18 11:41:21.883 demo[17675:3084893] 給五個人買飯帶回宿舍----<NSThread: 0x600000071200>{number = 3, name = (null)}
2017-06-18 11:41:21.885 demo[17675:3084893] 給五個人買飯帶回宿舍----<NSThread: 0x600000071200>{number = 3, name = (null)}
2017-06-18 11:41:21.886 demo[17675:3084893] 給五個人買飯帶回宿舍----<NSThread: 0x600000071200>{number = 3, name = (null)}
2017-06-18 11:41:21.888 demo[17675:3084893] 給五個人買飯帶回宿舍----<NSThread: 0x600000071200>{number = 3, name = (null)}
2017-06-18 11:41:21.888 demo[17675:3084893] 給五個人買飯帶回宿舍----<NSThread: 0x600000071200>{number = 3, name = (null)}
2017-06-18 11:41:21.894 demo[17675:3084895] 五個人開始吃飯----<NSThread: 0x60800006c600>{number = 4, name = (null)}
2017-06-18 11:41:21.895 demo[17675:3084895] 五個人開始吃飯----<NSThread: 0x60800006c600>{number = 4, name = (null)}
2017-06-18 11:41:21.896 demo[17675:3084895] 五個人開始吃飯----<NSThread: 0x60800006c600>{number = 4, name = (null)}
2017-06-18 11:41:21.897 demo[17675:3084895] 五個人開始吃飯----<NSThread: 0x60800006c600>{number = 4, name = (null)}
2017-06-18 11:41:21.898 demo[17675:3084895] 五個人開始吃飯----<NSThread: 0x60800006c600>{number = 4, name = (null)}
註：可以看出當買飯的操作完成後，開啟一個新線程執行吃飯操作。
iOS多線程---NSOperation的常用操作