Question

如何先执行block中的代码后在执行下面的代码

Answer 1

- (CLPlacemark*)getStartplacemark
{
//先创建一个semaphore
dispatch_queue_t queue = dispatch_get_global_queue(0, 0);
dispatch_semaphore_t semaphore = dispatch_semaphore_create(1);
__block CLPlacemark* start;
[self.geoCoder geocodeAddressString:_SourceText.text completionHandler:^(NSArray *placemarks, NSError *error) {
CLPlacemark *startPlaceMark = [placemarks firstObject];
start = startPlaceMark;

//发出已完成的信号
dispatch_semaphore_signal(semaphore);
}];

//等待执行，不会占用资源
dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
return start;
}