我尝试将起点和终点本地化为地址字符串,以便将其存储到NSUserDefaults
中。问题在于该方法继续执行,并且未设置我的变量。
NSLog(@"Begin");
__block NSString *returnAddress = @"";
[self.geoCoder reverseGeocodeLocation:self.locManager.location completionHandler:^(NSArray *placemarks, NSError *error) {
if(error){
NSLog(@"%@", [error localizedDescription]);
}
CLPlacemark *placemark = [placemarks lastObject];
startAddressString = [NSString stringWithFormat:@"%@ %@\n%@ %@\n%@\n%@",
placemark.subThoroughfare, placemark.thoroughfare,
placemark.postalCode, placemark.locality,
placemark.administrativeArea,
placemark.country];
returnAddress = startAddressString;
//[self.view setUserInteractionEnabled:YES];
}];
NSLog(returnAddress);
NSLog(@"Einde");
这是我的应用程序调试器显示的内容:
开始
爱因德
例如,如果我的所在地地址为:“Mainstreet 32,CITY”。然后,我想看的是以下内容:
开始
城市Mainstreet 32
爱因德
问题是我的代码没有等待
CLGeocoder
完成,因此返回时未设置我的变量returnAddress
,并且它为空。有谁知道如何解决这个问题?
最佳答案
因为reverseGeocodeLocation
有一个完成块,所以当执行到达时,它会移交给另一个线程-但在主线程上的执行仍将继续进行下一个操作,即NSLog(returnAddress)
。此时,尚未设置returnAddress
,因为reverseGeocodeLocation
刚刚移交给了另一个线程。
在使用完成块时,您必须开始考虑异步工作。
考虑将reverseGeocodeLocation
保留为方法中的最后一个操作,然后使用完成块中的其余逻辑来调用新方法。这将确保在您拥有returnAddress
的值之前,逻辑不会执行。
- (void)someMethodYouCall
{
NSLog(@"Begin");
__block NSString *returnAddress = @"";
[self.geoCoder reverseGeocodeLocation:self.locManager.location completionHandler:^(NSArray *placemarks, NSError *error) {
if(error){
NSLog(@"%@", [error localizedDescription]);
}
CLPlacemark *placemark = [placemarks lastObject];
startAddressString = [NSString stringWithFormat:@"%@ %@\n%@ %@\n%@\n%@",
placemark.subThoroughfare, placemark.thoroughfare,
placemark.postalCode, placemark.locality,
placemark.administrativeArea,
placemark.country];
returnAddress = startAddressString;
//[self.view setUserInteractionEnabled:YES];
NSLog(returnAddress);
NSLog(@"Einde");
// call a method to execute the rest of the logic
[self remainderOfMethodHereUsingReturnAddress:returnAddress];
}];
// make sure you don't perform any operations after reverseGeocodeLocation.
// this will ensure that nothing else will be executed in this thread, and that the
// sequence of operations now follows through the completion block.
}
- (void)remainderOfMethodHereUsingReturnAddress:(NSString*)returnAddress {
// do things with returnAddress.
}
或者,您可以在
reverseGeocodeLocation
完成后使用NSNotificationCenter发送通知。您可以在其他需要的地方订阅这些通知,并从那里完成逻辑。将[self remainderOfMethodHereWithReturnAddress:returnAddress];
替换为:NSDictionary *infoToBeSentInNotification = [NSDictionary dictionaryWithObject:returnAddress forKey:@"returnAddress"];
[[NSNotificationCenter defaultCenter]
postNotificationName:@"NameOfNotificationHere"
object:self
userInfo: infoToBeSentInNotification];
}];
Here's使用NSNotificationCenter的示例。