Question

I am having some problems with changing an image view inside of an MKAnnotationView subclass. I have a timer that updates the annotation position based on data about where a user was at a certain point. This works fine and the annotation position is updated correctly. I do this with the following code:

[_myAnnotation setCoordinate:point.position];

Below this, I also calculate whether the user was heading east or west. If the user is heading east, I call the setIsMovingRight:YES method on the MyAnnotation class, and do the opposite for when the user is heading west.

I have verified that the method is being called with the correct values at the correct times by using NSLog inside the method to print out whenever the value changes. However, it doesn’t seem like the setIsMovingRight method has any effect on the visual appearance of the annotation. I try setting the background colour of the imageview to red whenever the method is called, but even this has no effect. I have tried calling setNeedsDisplay in various places with no success.

I can add and recreate an annotation view, but then the annotation flashes on and off whenever the position changes and it really does not look very good.

The following is the code for my custom annotation view, “MyAnnotation”.

@interface MyAnnotation : MKAnnotationView <MKAnnotation>
{
    UIImageView *_imageView;
    BOOL _currentlyMovingRight;
}

@property (nonatomic) CLLocationCoordinate2D coordinate;
@property (nonatomic, copy) NSString *title;
@property (nonatomic, copy) NSString *subtitle;

@property (nonatomic,retain) UIImage  *image;

-(void)setIsMovingRight:(BOOL)movingRight;

@end

@implementation MyAnnotation

@synthesize coordinate, title, subtitle, image;

-(id)initWithAnnotation:(id<MKAnnotation>)annotation reuseIdentifier:(NSString *)reuseIdentifier
{
    self = [super initWithAnnotation:annotation reuseIdentifier:reuseIdentifier];
    if(self)
    {
        _currentlyMovingRight = NO;
        _imageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"right.png"]];
        [self addSubview:_imageView];
    }
    return self;
}

-(void)setIsMovingRight:(BOOL)movingRight
{
    _imageView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, 30, 30)];
    [_imageView setBackgroundColor:[UIColor redColor]]; // THIS LINE NEVER DOES ANYTHING.

    if(movingRight && !_currentlyMovingRight)
    {
        NSLog(@"right now.");
        [_imageView setImage:[UIImage imageNamed:@"right.png"]];
    }
    else if (!movingRight && _currentlyMovingRight)
    {
        NSLog(@"left now.");
        [_imageView setImage:[UIImage imageNamed:@"left.png"]];
    }
    _currentlyMovingRight = movingRight;

    [self addSubview:_imageView];
    [self setNeedsDisplay];
}

I would appreciate any help or advice that anyone could give. Thanks!

Answer 1

I think that the annotation views use KVO to listen for changes. Have you tried changing the image property? Something like [self setImage:myNewImage]