ios - 更新时自定义注释不会在 map View 上更新

Question

我正在执行 willChangeValueForKey 和 didChangeValueForKey 调用，但即使使用它们，mapView 委托(delegate)也永远不会运行通过 mapView: viewForAnnotation: 来更新事情。如何强制更新 MKAnnotation？

当图像更改时，annotationView.image 不会更新，annotationView.image 也不会更新。据我所知，通过我的 NSLog 行，当 MKAnnotation 更新时，mapView: viewForAnnotation: 不会被再次调用。

.h

#import <UIKit/UIKit.h>
#import <Foundation/Foundation.h>
#import <MapKit/MapKit.h>

@interface MapAnnotation : NSObject <MKAnnotation>

@property (nonatomic, assign) CLLocationCoordinate2D coordinate;
@property (nonatomic, retain) NSString *currentTitle;
@property (nonatomic, retain) NSString *currentSubTitle;
@property (nonatomic, retain) NSString *category;
@property (nonatomic, retain) NSString *pin;

- (NSString*) title;
- (NSString*) subtitle;
- (id) initWithCoordinate:(CLLocationCoordinate2D) c;
- (CLLocationCoordinate2D) getCoordinate;
- (void) addPlace:(MapAnnotation*) place;
- (int) placesCount;
- (void) cleanPlaces;
- (UIImage *) getPin;
@end

.m

#import "MapAnnotation.h"

@interface MapAnnotation()
@property (strong) NSMutableArray *places;
@end

@implementation MapAnnotation

@synthesize coordinate      = _coordinate;
@synthesize currentTitle    = _currentTitle;
@synthesize currentSubTitle = _currentSubTitle;
@synthesize places          = _places;
@synthesize category        = _category;
@synthesize pin             = _pin;


- (NSString*) subtitle {
    if ([self placesCount] == 1) {
        return self.currentSubTitle;
    }
    else{
        return @"";
    }
}


- (NSString*) title {
    if ([self placesCount] == 1) {
        return self.currentTitle;
    }
    else{
        return [NSString stringWithFormat:@"%d places", [self placesCount]];
    }
}


- (void)addPlace:(MapAnnotation *)place {
    [self willChangeValueForKey:@"title"];
    [self willChangeValueForKey:@"subtitle"];
    [self.places addObject:place];
    [self didChangeValueForKey:@"title"];
    [self didChangeValueForKey:@"subtitle"];
}


- (CLLocationCoordinate2D)getCoordinate {
    return self.coordinate;
}


- (void)cleanPlaces {
    [self willChangeValueForKey:@"title"];
    [self willChangeValueForKey:@"subtitle"];
    [self.places removeAllObjects];
    [self.places addObject:self];
    [self didChangeValueForKey:@"title"];
    [self didChangeValueForKey:@"subtitle"];
}


- (id)initWithCoordinate:(CLLocationCoordinate2D) c {
    self.coordinate=c;
    self.places=[[NSMutableArray alloc] initWithCapacity:0];
    return self;
}


- (int)placesCount {
    return [self.places count];
}


- (UIImage *)getPin {
    // begin a graphics context of sufficient size
    CGSize size = CGSizeMake(26, 26);
    UIGraphicsBeginImageContextWithOptions(size, NO, 0.0);

    // get the context for CoreGraphics
    CGContextRef ctx = UIGraphicsGetCurrentContext();

    CGRect imageRect = CGRectMake(0, 0, size.width, size.height);

    // Draw Dot
    CGRect circleRect = CGRectInset(imageRect, 4, 4);
    [[UIColor blackColor] setStroke];
    [[UIColor yellowColor] setFill];
    CGContextFillEllipseInRect(ctx, circleRect);
    CGContextStrokeEllipseInRect(ctx, circleRect);

    // Dot Content
    [[UIColor blackColor] setStroke];
    [[UIColor blackColor] setFill];
    CGAffineTransform transform = CGAffineTransformMake(1.0, 0.0, 0.0, -1.0, 0.0, 0.0);
    CGContextSetTextMatrix(ctx, transform);
    CGContextSetLineWidth(ctx, 2.0);
    CGContextSetCharacterSpacing(ctx, 1.7);
    CGContextSetTextDrawingMode(ctx, kCGTextFill);
    UIFont *font = [UIFont fontWithName:@"Arial" size:11.0];
    if ([self placesCount] != 1) {
        NSString *label = [NSString stringWithFormat:@"%d", [self placesCount]];
        CGSize stringSize = [label sizeWithAttributes:@{NSFontAttributeName:font}];
        [label drawAtPoint:CGPointMake(size.width / 2 - stringSize.width / 2, size.height / 2 - stringSize.height / 2)
            withAttributes:@{NSFontAttributeName:font}];
    } else {
        NSString *label = [NSString stringWithFormat:@"%@", self.pin];
        CGSize stringSize = [label sizeWithAttributes:@{NSFontAttributeName:font}];
        [label drawAtPoint:CGPointMake(size.width / 2 - stringSize.width / 2, size.height / 2 - stringSize.height / 2)
            withAttributes:@{NSFontAttributeName:font}];
    }


    // make image out of bitmap context
    UIImage *retImage = UIGraphicsGetImageFromCurrentImageContext();

    // free the context
    UIGraphicsEndImageContext();

    return retImage;
}

@end

map View :viewForAnnotation:

- (MKAnnotationView *)mapView:(MKMapView *)mapView viewForAnnotation:(id <MKAnnotation>)annotation {
    MKAnnotationView *annotationView = [mapView dequeueReusableAnnotationViewWithIdentifier:@"MyAnnoation"];
    if(!annotationView) {
        annotationView = [[MKAnnotationView alloc] initWithAnnotation:annotation reuseIdentifier:@"MyAnnoation"];
        annotationView.rightCalloutAccessoryView = [UIButton buttonWithType:UIButtonTypeDetailDisclosure];
    }

    annotationView.enabled = YES;
    if ([(MapAnnotation*)annotation placesCount] == 1) {
        annotationView.canShowCallout = YES;
    }
    annotationView.image = [(MapAnnotation*)annotation getPin];
    NSLog(@"%@", [annotation title]);

    return annotationView;
}

Answer 1

如评论中所述，除了 title 和 subtitle 之外，注释属性的更改不会自动导致 View 更新。

更改 title 和 subtitle 将在显示时自动更新标注，只要更改导致 KVO 通知(例如，如果使用带有 ann.title = xxx 或通过手动发出 KVO 通知作为问题中的代码，因为您有自定义 getter)。

要自动更新图像，您可能需要使用自定义注释 View 来观察底层注释属性的变化并自行刷新(在 init 中调用 addObserver , 在 observeValueForKeyPath 更新图像, 在 dealloc 调用 removeObserver).您也可以使用非 KVO 方法来完成它，例如自定义通知或委托(delegate)(但仍然使用自定义注释 View )。

在现有代码中，无需创建自定义注解 View 和使用KVO等即可快速手动更新注解 View 的方法是在注解更新后立即获取注解的当前 View 并更新图像 属性。只要 viewForAnnotation 中的代码与设置 image 的逻辑相同，这就应该有效。

我假设在应用程序的某处(有时在注释已添加之后)，它正在通过调用 addPlace 更新注释中的位置。之后，您可以尝试以下操作:

[someExistingAnnotation addPlace:anotherPlace];

//obtain the current view of someExistingAnnotation...
MKAnnotationView *av = [mapView viewForAnnotation:someExistingAnnotation];

//update its image property to force refresh...
av.image = [someExistingAnnotation getPin];
//also set canShowCallout (it might have been NO)

不相关，但当前的 viewForAnnotation 没有正确处理可能的 View 重用和/或自定义注释以外的注释类型(例如用户位置蓝点，这会导致当前代码崩溃)。我建议将其更改为:

- (MKAnnotationView *)mapView:(MKMapView *)mapView viewForAnnotation:(id <MKAnnotation>)annotation {
    if (! [annotation isKindOfClass:[MapAnnotation class]])
    {
        //annotation is NOT a "MapAnnotation", return nil for default view...
        return nil;
    }

    MKAnnotationView *annotationView = [mapView dequeueReusableAnnotationViewWithIdentifier:@"MyAnnoation"];
    if(!annotationView) {
        annotationView = [[MKAnnotationView alloc] initWithAnnotation:annotation reuseIdentifier:@"MyAnnoation"];
        annotationView.rightCalloutAccessoryView = [UIButton buttonWithType:UIButtonTypeDetailDisclosure];
    }

    //update view's annotation to current in case it's being re-used
    annotationView.annotation = annotation;

    annotationView.enabled = YES;
    if ([(MapAnnotation*)annotation placesCount] == 1) {
        annotationView.canShowCallout = YES;
    }
    else {
        annotationView.canShowCallout = NO;
    }

    annotationView.image = [(MapAnnotation*)annotation getPin];
    NSLog(@"%@", [annotation title]);

    return annotationView;
}