iOS7 RMMapView可以'；不要把所有的瓷砖都装上

我正在使用MapBox SDK，并且已经生成了.mbtiles文件。 但是，当我将它与RMMapView一起使用时，它只能加载一小部分。为什么不是所有的瓷砖都装上了？ 例如，zoomlevel 0中应该有16个平铺，但我只能看到2个

    - (void)viewDidLoad
{
    [super viewDidLoad];
    RMMBTilesSource *offlineSource = [[RMMBTilesSource alloc] initWithTileSetURL:[NSURL fileURLWithPath:[[NSBundle mainBundle] pathForResource:@"nn" ofType:@"mbtiles"]]];
    RMMapView *mapView = [[RMMapView alloc] initWithFrame:self.view.bounds andTilesource:offlineSource];

    // default zoom
    mapView.zoom = 0;
    // hard code minimal zoom. Try to run in without it to see what happens.
    mapView.minZoom = 0;
    mapView.maxZoom = 3;
    // hide MapBox logo
    mapView.showLogoBug = NO;
    // hide bottom right "i" icon
    [mapView setHideAttribution:YES];

    mapView.autoresizingMask = UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleWidth;
    mapView.adjustTilesForRetinaDisplay = YES; // these tiles aren't designed specifically for retina, so make them legible

    [self.view addSubview:mapView];
    // Do any additional setup after loading the view, typically from a nib.
}

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您是如何生成MBTiles文件的？您是否在其他客户端尝试过，例如上载到mapbox.com？您还可以在

RMMBTilesSource

中设置断点，以查看是否正在加载磁贴