iOS block备忘录03

Block的常见几个用途

1.简化枚举

NSArray *array = ...
    [array enumerateObjectsUsingBlock:^ (id obj, NSUInteger idx, BOOL *stop) {
        NSLog(@"Object at index %lu is %@", idx, obj);
    }];

2.简化并发任务

• 使用于OperationQueue

NSBlockOperation *operation = [NSBlockOperation blockOperationWithBlock:^{
    ...
}];

// schedule task on main queue:
NSOperationQueue *mainQueue = [NSOperationQueue mainQueue];
[mainQueue addOperation:operation];

// schedule task on background queue:
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
[queue addOperation:operation];

• 使用于GCD

dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);

dispatch_async(queue, ^{
    NSLog(@"Block for asynchronous execution");
});