6.14 Creating Dependency Between Operations-优快云博客

本文通过一个具体的示例展示了如何使用 NSOperation 和 NSOperationQueue 在 iOS 开发中管理任务间的依赖关系，确保一个操作在另一个操作完成后才开始执行。

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在某个任务完成后才开始另一个任务

没什么好说的，上例子

- (void) firstOperationEntry:(id)paramObject{

NSLog(@"First Operation - Parameter Object = %@", paramObject);

NSLog(@"First Operation - Main Thread = %@", [NSThread mainThread]);

NSLog(@"First Operation - Current Thread = %@", [NSThread currentThread]);

}

- (void) secondOperationEntry:(id)paramObject{

NSLog(@"Second Operation - Parameter Object = %@", paramObject);

NSLog(@"Second Operation - Main Thread = %@", [NSThread mainThread]);

NSLog(@"Second Operation - Current Thread = %@", [NSThread currentThread]);

}

-(void)test6_14

{

NSNumber *firstNumber = [NSNumber numberWithInteger:111];

NSNumber *secondNumber = [NSNumber numberWithInteger:222];

NSInvocationOperation *firstOperation;

NSInvocationOperation *secondOperation;

NSOperationQueue *operationQueue;

firstOperation = [[NSInvocationOperation alloc] initWithTarget:self

selector:@selector(firstOperationEntry:) object:firstNumber];

secondOperation = [[NSInvocationOperation alloc] initWithTarget:self

selector:@selector(secondOperationEntry:) object:secondNumber];

[firstOperation addDependency:secondOperation];

// [firstOperation removeDependency:secondOperation];

operationQueue = [[NSOperationQueue alloc] init];

/* Add the operations to the queue */

[operationQueue addOperation:firstOperation];

[operationQueue addOperation:secondOperation];

NSLog(@"Main thread is here");

}

输出：

2014-03-12 10:27:22.158 cookbook[505:a0b] Main thread is here

2014-03-12 10:27:22.158 cookbook[505:1403] Second Operation - Parameter Object = 222

2014-03-12 10:27:22.159 cookbook[505:1403] Second Operation - Main Thread = <NSThread: 0x8950130>{name = (null), num = 1}

2014-03-12 10:27:22.159 cookbook[505:1403] Second Operation - Current Thread = <NSThread: 0x8c917d0>{name = (null), num = 2}

2014-03-12 10:27:22.160 cookbook[505:1403] First Operation - Parameter Object = 111

2014-03-12 10:27:22.160 cookbook[505:1403] First Operation - Main Thread = <NSThread: 0x8950130>{name = (null), num = 1}

2014-03-12 10:27:22.161 cookbook[505:1403] First Operation - Current Thread = <NSThread: 0x8c917d0>{name = (null), num = 2}

显然firstOperation是在secondOperation执行完成后才开始执行的。这是通过[firstOperation addDependency:secondOperation];这句实现的。

如果想取消这种依赖关系，则用 [firstOperation removeDependency:secondOperation];