iphone - 如何给MKMapView异步添加注解？

Question

我有很多注释要添加到 mkmapview 中。当我添加注释时，应用程序会短时间卡住。我知道主线程是唯一允许添加 UI 以查看的线程，如果这是真的，我如何让这个操作不卡住应用程序？

// in viewdidLoad
for (NSManagedObject *object in requestResults) {
     CustomAnnotation *customAnnotation = [[CustomAnnotation alloc] init];
     customAnnotation.title = object.title;
     customAnnotation.coordinate = CLLocationCoordinate2DMake([object.latitude doubleValue], [object.longitude doubleValue]);
     [_mapView addAnnotation:customAnnotation];
} 
} // end viewdidload

- (MKAnnotationView *)mapView:(MKMapView *)mapView viewForAnnotation:(id<MKAnnotation>)annotation
{
// shows the annotation with a custom image
    MKPinAnnotationView *customPinView = [[MKPinAnnotationView alloc] initWithAnnotation:annotation reuseIdentifier:@"mapAnnotation"];
    CustomAnnotation *customAnnotation = (id) annotation;
    customPinView.image = [UIImage imageNamed:@"green"];
    return customPinView;
}

Answer 1

您可以使用 Grand Central Dispatch - GCD为此。

尝试:

- (void)viewDidLoad
{
  dispatch_async(dispatch_get_global_queue(0, 0), ^{
     for (NSManagedObject *object in requestResults)
     {
        CustomAnnotation *customAnnotation = [[CustomAnnotation alloc] init];
        customAnnotation.title = object.title;
        customAnnotation.coordinate = CLLocationCoordinate2DMake([object.latitude doubleValue], [object.longitude doubleValue]);
        dispatch_async(dispatch_get_main_queue(), ^{
           [_mapView addAnnotation:customAnnotation];
        });
     }
  });
}

这是一个很好的教程:GCD and threading