记录NSOperation用法.

NSOperation *operation = [NSInvocationOperation alloc] initWithTarget:self selector:@selector(run) object:nil];

[operation start];

NSBlockOperation *operation1 = [NSBlockOperation blockOperationWithBlock:^{

doSomeThing();

}]

[operation1 addExcutionBlock:^{

doSomeThing();

[NSThread sleepForTimeInterVal:2];

}]

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

queue.maxConcurrentOperationCount = 2; // 2～3

[queue addOperation:operation]; // auto-run

[queue setSuspended:YES];

[operation addDependency:operation]; // appliable on different queue

operation.completionBolck = ^{ };