Question

我正在处理从MapServer加载的滚动视图中显示多个图像，这些图像返回显示地图的图像。所以我做的是创建了4个UIImageViews，将它们放在NSMutableDictionary中。然后当滚动到所需的Image时，它将启动从url异步加载数据。所以首先我显示一个UIActivityIndicatorView，然后它将加载数据，最后隐藏UIActivityIndicatorView并显示UIImageView。

除了在图像显示之前需要很长时间，所有内容都或多或少都有效，尽管图像不是那么大，但我有一个日志文本，表明函数的结尾已到达...此日志消息出现立即但图像仍然没有显示... 如果我通过Webbrowser调用URL，也会立即显示图像。

下面你看到我的代码。

- (void) loadSRGImage:(int) page {

UIImageView *currentSRGMap   = (UIImageView *)[srgMaps objectForKey:[NSString stringWithFormat:@"image_%i", page]];
UIActivityIndicatorView *currentLoading  = (UIActivityIndicatorView *)[srgMaps objectForKey:[NSString stringWithFormat:@"loading_%i", page]];


// if the image has been loaded already, do not load again
if ( currentSRGMap.image != nil ) return;

if ( page > 1 ) {

    MKCoordinateSpan currentSpan;
    currentSpan.latitudeDelta   = [[[srgMaps objectForKey:[NSString stringWithFormat:@"span_%i", page]] objectForKey:@"lat"] floatValue];
    currentSpan.longitudeDelta  = [[[srgMaps objectForKey:[NSString stringWithFormat:@"span_%i", page]] objectForKey:@"lon"] floatValue];

    region.span         = currentSpan;
    region.center       = mapV.region.center;
    [mapV setRegion:region animated:TRUE];
    //[mapV regionThatFits:region];
}
srgLegende.hidden = NO;

currentSRGMap.hidden = YES;
currentLoading.hidden = NO;
[currentLoading startAnimating];

NSOperationQueue *queue = [NSOperationQueue new];
NSInvocationOperation *operation = [[NSInvocationOperation alloc] 
                                    initWithTarget:self
                                    selector:@selector(loadImage:) 
                                    object:[NSString stringWithFormat:@"%i", page]];

[queue addOperation:operation]; 
[operation release];

}

- (void) loadImage:(NSInvocationOperation *) operation {

NSString *imgStr = [@"image_" stringByAppendingString:(NSString *)operation];
NSString *loadStr = [@"loading_" stringByAppendingString:(NSString *)operation];

WGS84ToCH1903 *converter = [[WGS84ToCH1903 alloc] init];

CLLocationCoordinate2D coord1   = [mapV convertPoint:mapV.bounds.origin toCoordinateFromView:mapV];
CLLocationCoordinate2D coord2   = [mapV convertPoint:CGPointMake(mapV.bounds.size.width, mapV.bounds.size.height) toCoordinateFromView:mapV];
int x1 = [converter WGStoCHx:coord1.longitude withLat:coord1.latitude];
int y1 = [converter WGStoCHy:coord1.longitude withLat:coord1.latitude];
int x2 = [converter WGStoCHx:coord2.longitude withLat:coord2.latitude];
int y2 = [converter WGStoCHy:coord2.longitude withLat:coord2.latitude];

NSString *URL = [NSString stringWithFormat:@"http://map.ssatr.ch/mapserv?mode=map&map=import/dab/maps/dab_online.map&mapext=%i+%i+%i+%i&mapsize=320+372&layers=DAB_Radio_Top_Two", y1, x1, y2, x2];

NSData* imageData = [[NSData alloc] initWithContentsOfURL:[NSURL URLWithString:URL]];
UIImage* image = [[UIImage alloc] initWithData:imageData];
[imageData release];

UIImageView *currentSRGMap   = (UIImageView *)[srgMaps objectForKey:imgStr];
UIActivityIndicatorView *currentLoading  = (UIActivityIndicatorView *)[srgMaps objectForKey:loadStr];

currentSRGMap.hidden = NO;
currentLoading.hidden = YES;
[currentLoading stopAnimating];

[currentSRGMap setImage:image]; //UIImageView
[image release];

NSLog(@"finished loading image: %@", URL);

}

Answer 1

我的应用中有类似的内容，我使用https://github.com/rs/SDWebImage中的SDWebImage。这个类别写在UIImageView上。您需要向UIImageView提及占位符图片和网址。它将在下载后显示图像，并维护下载图像的缓存，从而避免多个服务器调用。

iPhone UIImageView在setImage时延迟显示

1 个答案: