ios - 在背景中为 map 添加注释

Question

我尝试将我的核心数据实体作为注释添加到 mapview 并且它有效但我有两个问题 1-它只显示第一张注释图片而另一个注释具有正常的图钉图像(我想我必须在后台执行此操作但是我不知道我该怎么做)2-我需要获得选定的实体(注释)我该怎么做？

-(void)viewDidAppear:(BOOL)animated{
    [super viewDidAppear:animated];

    //add each object in Contacts entity to map view
    NSManagedObjectContext *context = [self managedObjectContext];
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription
                                   entityForName:@"Contacts" inManagedObjectContext:context];
    [fetchRequest setEntity:entity];
    NSArray *fetchedObjects = [context executeFetchRequest:fetchRequest error:nil];



    for (info in fetchedObjects) {
        NSLog(@"Name: %@", [info valueForKey:@"name"]);

        //initializetion latitude and longitude
        aLng=[[info  valueForKey:@"lng"] doubleValue];
        aLat=[[info  valueForKey:@"lat"] doubleValue];
        //if latitude and longitude not null
        if(aLng && aLat && aLng!=0.0 &&aLat!=0.0)
        {
            //create a new Coordinate
            CLLocationCoordinate2D wimLocation;
            wimLocation.latitude=aLat;
            wimLocation.longitude=aLng;

            //create a new Annotation and initializetion it
            MKPointAnnotation * myAnnotation=[MKPointAnnotation alloc];
            myAnnotation.coordinate=wimLocation;
            myAnnotation.title=[info valueForKey:@"name"];



            //add create Annotation to mapview
            [self.mapview addAnnotation:myAnnotation];


            //default region Iran,Tehran
            CLLocationCoordinate2D Location;
            Location.latitude=35.696111;
            Location.longitude=51.423056;
            MKCoordinateRegion region;
            MKCoordinateSpan span;
            span.latitudeDelta=50.0; // change as per your zoom level
            span.longitudeDelta=50.0;
            region.span=span;
            region.center= Location;
            [self.mapview setRegion:region animated:TRUE];
            [self.mapview regionThatFits:region];

        }
    }

}


- (MKAnnotationView *)mapView:(MKMapView *)mapView viewForAnnotation:(id <MKAnnotation>)annotation
{

    // initializetion pinImage with contact image
    UIImage *img = [UIImage imageWithData:[info valueForKey:@"photo"]];
    if(img){
        // If it's the user location, just return nil.
        if ([annotation isKindOfClass:[MKUserLocation class]])
            return nil;

        // Handle any custom annotations.
        if ([annotation isKindOfClass:[MKPointAnnotation class]])
        {
            // Try to dequeue an existing pin view first.
            MKAnnotationView *pinView = (MKAnnotationView*)[mapView dequeueReusableAnnotationViewWithIdentifier:@"CustomPinAnnotationView"];
            if (!pinView)
            {

                // If an existing pin view was not available, create one.
                pinView = [[MKAnnotationView alloc] initWithAnnotation:annotation reuseIdentifier:@"CustomPinAnnotationView"];
                //pinView.animatesDrop = YES;
                pinView.canShowCallout = YES;
                //image size

                CGSize destinationSize = CGSizeMake(35, 40);
                UIGraphicsBeginImageContext(destinationSize);
                [img drawInRect:CGRectMake(0,0,destinationSize.width,destinationSize.height)];
                UIImage *pinImage = UIGraphicsGetImageFromCurrentImageContext();
                UIGraphicsEndImageContext();


                pinView.image = pinImage;

                pinView.calloutOffset = CGPointMake(10, -20);


            } else {
                pinView.annotation = annotation;
            }
            return pinView;
        }
    }
    return nil;

}

Answer 1

显然，info 是您在循环中一次又一次覆盖的局部变量。

相反，您应该获得正确的 Contacts 托管对象来填充您的注释。 NSFetchedResultsController 在我看来是最好的解决方案。