用户位置图片图钉大部分时间消失

Question

i Am using following code

-(MKAnnotationView *) mapView:(MKMapView *)mapView viewForAnnotation:(id<MKAnnotation>)annotation
{
    if ([[annotation title] isEqualToString:@"Current Location"] )
    {
        MKAnnotationView *anView = [[MKAnnotationView alloc] initWithAnnotation:annotation reuseIdentifier:@"currentPin"];

        anView.image = [UIImage imageNamed:@"pin_green.png"];
        anView.canShowCallout = true;
        anView.enabled = true;
        return anView;
    }

The issue is, it randomly disappears and appears again. Giving a very bad user experience. Any way to fix this?

Answer 1

You should use MKMapView's dequeueReusableAnnotationViewWithIdentifier: and see if you get a view back before creating a new one with initWithAnnotation:reuseIdentifier: :

MKAnnotationView *anView = [mapView dequeueReusableAnnotationViewWithIdentifier:@"currentPin"];

if (!anView) {
    anView = [[MKAnnotationView alloc] initWithAnnotation:annotation reuseIdentifier:@"currentPin"];

    anView.image = [UIImage imageNamed:@"pin_green.png"];
    anView.canShowCallout = true;
    anView.enabled = true;
}

return anView;

That said, I'm not entirely sure this is the cause of your problem.

Answer 2

There are several suspect things about this code:

• You're not using dequeue , as someone has pointed out. In particular, the problem here is that you are making a new view every single time, rather than checking to see whether a new view needs making.

• You are forgetting the key step, namely, to associate the view with the annotation.

Here is the canonical structure of a simple viewForAnnotation: implementation where we supply our own view:

- (MKAnnotationView *)mapView:(MKMapView *)mapView
            viewForAnnotation:(id <MKAnnotation>)annotation {
    MKAnnotationView* v = nil;
    if ([annotation.title isEqualToString:@"Current Location"]) {
        static NSString* ident = @"greenPin";
        v = [mapView dequeueReusableAnnotationViewWithIdentifier:ident];
        if (v == nil) {
            v = [[MKAnnotationView alloc] initWithAnnotation:annotation
                                              reuseIdentifier:ident];
            v.image = [UIImage imageNamed:@"pin_green.png"];
            v.canShowCallout = YES;
        }
        v.annotation = annotation;
    }
    return v;
}

Since that code works for me, I'd suggest you start with it and tweak it as necessary.

By the way, you do NOT need this method just to get a green pin! You do know that, right? iOS will give you a green pin (MKPinAnnotationColorGreen).