添加到 NSOperationQueue 时，具有依赖关系的 NSOperation 不会被执行
我试图弄清楚为什么带有依赖项的 NSOperation 在添加到 NSOperationQueue （iOS5，ARC）时没有被执行：
@implementation NSOperationTest {
NSOperationQueue *_operationQueue;
}
- (id)init {
self = [super init];
if (self) {
_operationQueue = [[NSOperationQueue alloc] init];
}
return self;
}
-(void) test
{
NSBlockOperation *op1 = [NSBlockOperation blockOperationWithBlock:^{
NSLog(@"op1 running");
}];
NSBlockOperation *op2 = [NSBlockOperation blockOperationWithBlock:^{
NSLog(@"op2 running");
}];
[op2 addDependency:op1];
[_operationQueue addOperation:op2];
}
@end
这让我发疯，这里 op1 应该在 op2，但其中任何一个都会被执行，当添加没有依赖项时，两者都可以正常工作。有人知道为什么吗？
提前致谢。
I'm trying to figure out why a NSOperation with a dependency is not being executed when added to NSOperationQueue (iOS5, ARC):
@implementation NSOperationTest {
NSOperationQueue *_operationQueue;
}
- (id)init {
self = [super init];
if (self) {
_operationQueue = [[NSOperationQueue alloc] init];
}
return self;
}
-(void) test
{
NSBlockOperation *op1 = [NSBlockOperation blockOperationWithBlock:^{
NSLog(@"op1 running");
}];
NSBlockOperation *op2 = [NSBlockOperation blockOperationWithBlock:^{
NSLog(@"op2 running");
}];
[op2 addDependency:op1];
[_operationQueue addOperation:op2];
}
@end
This is getting me crazy, here op1 is supposed to be executed before op2, but either is executed, when added without dependencies both works just fine. Does someone knows why?
Thanks in advance.
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您必须向操作队列显式执行任何操作（或直接执行它）才能执行 - 依赖项也不例外。如果不这样做（就像您所做的那样），
op2将永远不会执行，因为它正在等待op1执行，而op1从未被告知过执行。因此，通过在test方法末尾添加[_operationQueue addOperation: op1];，您的问题应该得到解决。You have to explicitly any operation to the operation queue (or execute it directly) in order for it to execute - and dependencies are no exception. Without doing so (as you've done)
op2will never execute because it is waiting forop1to execute, whenop1has never been told to execute. So by adding[_operationQueue addOperation: op1];at the end of yourtestmethod, your problem should be fixed.