ios - setNeedsDisplayInMapRect不会触发新的drawMapRect : call

我正在使用自定义MKOverlay/MKOverlayView用我自己的图块完全覆盖Google basemap ，这些图块是异步加载的。当我收到对覆盖 View 的canDrawMapRect:zoomScale:调用(并在这种情况下返回FALSE)时，我遵循请求卸载图块的模式，然后在图块可用时调用setNeedsDisplayInMapRect:zoomScale:。

所有这些通常都可以正常运行，并且在模拟器中似乎可以完美运行。

但是，在设备上有时会在覆盖层上出现“洞”-缺少瓷砖。

我可以看到该图块已请求，并且请求已完成。我可以看到我叫setNeedsDisplayInMapRect:zoomScale:，并且传递了MKMapRect中提供的原始MKZoomScale和canDrawMapRect:zoomScale:。但我也可以看到，从未要求覆盖层重绘该图块(不再为该图块调用canDrawMapRect:zoomScale:和drawMapRect:zoomScale:inContext:)。

我需要了解为什么会发生这种情况以及如何纠正它。

这是我的MKOverlayView子类中的相关代码:

- (BOOL) canDrawMapRect: (MKMapRect) mapRect zoomScale: (MKZoomScale) zoomScale
{
    NSUInteger zoomLevel = [self zoomLevelForZoomScale:zoomScale];
    CGPoint mercatorPoint = [self mercatorTileOriginForMapRect:mapRect];
    NSUInteger tilex = floor(mercatorPoint.x * [self worldTileWidthForZoomLevel:zoomLevel]);
    NSUInteger tiley = floor(mercatorPoint.y * [self worldTileWidthForZoomLevel:zoomLevel]);

    NSURL* tileUrl = [self tileURLForZoomLevel: zoomLevel tileX: tilex tileY: tiley];

    ASIHTTPRequest* tileRequest = [ASIHTTPRequest requestWithURL: tileUrl];
    tileRequest.downloadCache = [ASIDownloadCache sharedCache];
    [tileRequest setCacheStoragePolicy:ASICachePermanentlyCacheStoragePolicy];

    if ( NO == [[ASIDownloadCache sharedCache] isCachedDataCurrentForRequest: tileRequest] )
    {
        [tileRequest setCachePolicy: ASIAskServerIfModifiedWhenStaleCachePolicy];
        tileRequest.delegate = self;
        tileRequest.userInfo = [NSDictionary dictionaryWithObjectsAndKeys:
                                [NSValue value: &mapRect withObjCType: @encode( MKMapRect )],       @"mapRect",
                                [NSValue value: &zoomScale withObjCType: @encode( MKZoomScale )],   @"zoomScale",
                                [NSNumber numberWithInt: tilex], @"tilex",
                                [NSNumber numberWithInt: tiley], @"tiley",
                                nil];

        [_tileRequestStack addOperation: tileRequest];

        NSLog( @"canDrawMapRect: %d, %d - REQUESTING", tilex, tiley );

        return NO;
    }

    NSLog( @"canDrawMapRect: %d, %d - READY", tilex, tiley );

    return YES;
}

- (void) drawMapRect: (MKMapRect) mapRect zoomScale: (MKZoomScale) zoomScale inContext: (CGContextRef) context
{
    NSUInteger zoomLevel = [self zoomLevelForZoomScale:zoomScale];

    CGPoint mercatorPoint = [self mercatorTileOriginForMapRect:mapRect];

    NSUInteger tilex = floor(mercatorPoint.x * [self worldTileWidthForZoomLevel:zoomLevel]);
    NSUInteger tiley = floor(mercatorPoint.y * [self worldTileWidthForZoomLevel:zoomLevel]);

    NSLog( @"drawMapRect:  %d, %d", tilex, tiley );

    NSURL* tileUrl = [self tileURLForZoomLevel: zoomLevel tileX: tilex tileY: tiley];
    NSData* tileData = [[ASIDownloadCache sharedCache] cachedResponseDataForURL: tileUrl];

    UIGraphicsPushContext(context);

    if ( tileData != nil )
    {
        UIImage* img = [UIImage imageWithData: tileData];

        if ( img != nil )
        {
            [img drawInRect: [self rectForMapRect: mapRect] blendMode: kCGBlendModeNormal alpha: 1.0 ];
        }
        else
        {
            NSLog( @"oops - no image" );
        }

        CGSize s = CGContextConvertSizeToUserSpace( context, CGSizeMake( 40, 1 ));

        UIFont* f = [UIFont systemFontOfSize: s.width];

        [[UIColor blackColor] setFill];

        [[NSString stringWithFormat: @"%d,%d", tilex, tiley] drawInRect: [self rectForMapRect: mapRect] withFont: f];
    }

    UIGraphicsPopContext();
}


- (void) requestFinished: (ASIHTTPRequest *) tileRequest
{
    NSValue* mapRectValue =  [tileRequest.userInfo objectForKey: @"mapRect"];
    MKMapRect mapRect;  [mapRectValue getValue: &mapRect];

    NSValue *zoomScaleValue = [tileRequest.userInfo objectForKey:@"zoomScale"];
    MKZoomScale zoomScale; [zoomScaleValue getValue: &zoomScale];

    NSLog( @"requestFinished: %d, %d, %lf",
          [[tileRequest.userInfo objectForKey:@"tilex"] intValue],
          [[tileRequest.userInfo objectForKey:@"tiley"] intValue],
          zoomScale  );

    [self setNeedsDisplayInMapRect: mapRect zoomScale: zoomScale];
}

编辑:I'm guessing that this is likely the issue.

最佳答案

我遇到的问题与此处描述的问题非常相似。就我而言，即使拥有最简单的代码，我也无法重现所需的行为(在http://developer.apple.com/library/ios/documentation/MapKit/Reference/MKOverlayView_class/Reference/Reference.html#//apple_ref/occ/instm/MKOverlayView/setNeedsDisplayInMapRect:zoomScale:中描述):

- (BOOL)canDrawMapRect:(MKMapRect)mapRect zoomScale:(MKZoomScale)zoomScale {
    NSLog(@"This should trace forever");

    [self setNeedsDisplayInMapRect:mapRect zoomScale:zoomScale];
    return NO;
}

或更接近我的原始代码:

- (BOOL)canDrawMapRect:(MKMapRect)mapRect zoomScale:(MKZoomScale)zoomScale {
    NSLog(@"This should trace forever");

    [SomeAsynchronousRequestWithCompletionHandler:^{
        [self setNeedsDisplayInMapRect:mapRect zoomScale:zoomScale];
    }];
    return NO;
}

在这两种情况下，setNeedsDisplayInMapRect:zoomScale:都从未被调用过。

当我开始运行setNeedsDisplayInMapRect:zoomScale:时，情况发生了变化，在dispatch_async内分派(dispatch)到可以运行canDrawMapRect的相同队列，例如:

- (BOOL)canDrawMapRect:(MKMapRect)mapRect zoomScale:(MKZoomScale)zoomScale {

    dispatch_queue_t queue = dispatch_get_current_queue();

    NSLog(@"This should trace forever");

    dispatch_async(queue, ^{
        [self setNeedsDisplayInMapRect:mapRect zoomScale:zoomScale];
    });

    return NO;
}

或包含异步作业:

- (BOOL)canDrawMapRect:(MKMapRect)mapRect zoomScale:(MKZoomScale)zoomScale {
    NSLog(@"This should trace forever");

    dispatch_queue_t queue = dispatch_get_current_queue();

    [SomeAsynchronousRequestWithCompletionHandler:^{
        dispatch_async(queue, ^{
            [self setNeedsDisplayInMapRect:mapRect zoomScale:zoomScale];
        });
    }];
    return NO;
}

使用dispatch_async-我可以看到不断跟踪的“这应该永远跟踪”字符串。我原来的问题也完全消失了。

最新消息:目前，我使用dispatch_get_main_queue()调用setNeedsDisplayInMapRect:zoomScale:

- (BOOL)canDrawMapRect:(MKMapRect)mapRect zoomScale:(MKZoomScale)zoomScale {
    NSLog(@"This should trace forever");

    [SomeAsynchronousRequestWithCompletionHandler:^{
        dispatch_async(dispatch_get_main_queue(), ^{
            [self setNeedsDisplayInMapRect:mapRect zoomScale:zoomScale];
        });
    }];
    return NO;
}