GCD使用（一）执行与UI有关的操作

1。使用GCD时，与UI有关的操作只能放在主线程中进行
dispatch_get_main_queue，

dispatch_async ( dispatch_queue_t queue, dispatch_block_t block) 异步执行，参数：操作队列，执行块

dispatch_async_f ( dispatch_queue_t queue,void *context,dispatch_function_t work) 异步执行，参数：操作队列，传入C函数的参数，执行C函数

e.g.

dispatch_queue_t mainQueue = dispatch_get_main_queue();

dispatch_async(mainQueue, ^(void) {

UIAlertView *alertView =[[UIAlertView alloc] initWithTitle:@"GCD" message:@"GCD is amazing!" delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil, nil];

[ alertView show];

NSLog(@"Current thread = %@", [NSThread currentThread]); //此处的操作均是在主线程中进行

NSLog(@"Main thread = %@", [NSThread mainThread]);

}) ;