iOS上的PNG验证 [英] PNG validation on iOS
问题描述
在iOS上编写地图应用程序,使用OpenStreetMap图块。
地图图块图像以异步方式下载并存储在字典中,或者保存在SQLite DB中。
Writing a mapping application on iOS, making use of OpenStreetMap tiles. Map tile images are downloaded asynchronously and stored in a dictionary, or persisted in a SQLite DB.
有时,无论出于何种原因,在尝试渲染地图时平铺图像,我收到以下错误:
ImageIO:< ERROR> PNGinvalid距离太远
Occasionally, for whatever reason, while attempting to render a map tile image, I get the following error:
ImageIO: <ERROR> PNGinvalid distance too far back
这会导致令人讨厌的黑色方块出现在我的地图上。
This causes nasty black squares to appear over my map.
这是发生这种情况的代码:
This is the piece of code in which this occurs:
NSData *imageData = [TileDownloader RetrieveDataAtTileX:(int)tilex Y:(int)tiley Zoom:(int)zoomLevel];
if (imageData != nil) {
NSLog(@"Obtained image data\n");
UIImage *img = [[UIImage imageWithData:imageData] retain];
// Perform the image render on the current UI context.
// ERROR OCCURS BETWEEN PUSH AND POP
UIGraphicsPushContext(context);
[img drawInRect:[self rectForMapRect:mapRect] blendMode:kCGBlendModeNormal alpha:1.0f];
UIGraphicsPopContext();
[img release];
}
现在,我正在寻找的方法是确保png是在尝试将其渲染到我的地图之前有效。
Now, what I'm looking for is a way to ensure a png is valid before attempting to render it to my map.
编辑:系统偶尔会抛出此错误:
ImageIO:< ERROR> PNGIDAT:CRC错误
The system also occasionally throws this error:
ImageIO: <ERROR> PNGIDAT: CRC error
推荐答案
从我自己的异步下载队列管理器切换到All Seeing I实现。问题变得没有实际意义。
Switched from my own Asynchronous Download Queue Manager to the All Seeing I implementation. Problem became a moot point.
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