问题描述
我在一个NSOperationQueue中有两个NSIvocationOperation.然后，我使用setQueuePriority来调整两个操作(1-> 2或2-> 1)的执行顺序.该代码在模拟器上运行良好，但是在我的iPhone上失败了.
I have two NSIvocationOperations in one NSOperationQueue. And I used setQueuePriority to adjust the execution order of the two operations, 1->2, or 2->1. The code worked well on emulator, however, failed on my iPhone.
我的代码是这样的:
NSOperationQueue *operationQueue = [[NSOperationQueue alloc] init];
operationQueue.maxConcurrentOperationCount = 1;
NSInvocationOperation *operation1 = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(thread1) object:nil];
[operation1 setQueuePriority:NSOperationQueuePriorityVeryLow];
NSInvocationOperation *operation2 = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(thread2) object:nil];
[operation2 setQueuePriority:NSOperationQueuePriorityHigh];
[operationQueue addOperation:operation1];
[operationQueue addOperation:operation2];
Operation2应该在operation1之前执行，我在模拟器上看到了相同的结果.在iPhone上，无论我如何调整其QueuePriorities，始终首先执行operation1.为什么会这样?
Operation2 should be executed ahead of operation1 and I saw the same result on emulator. While on iPhone, operation1 was always executed first no matter how I adjusted their QueuePriorities. Why it's like this?
推荐答案
队列优先级不能保证执行顺序.引用苹果的文档:
Queue priority doesn't guarantee execution order. To quote from Apple's documentation:
如果对您而言重要的是先执行一项操作，则应改为使用操作依赖项(通过 addDependency:).
If it's important to you that one operation be executed before another you should use operation dependencies instead (via addDependency:).
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