如何让CATiledLayer不阻塞主线程
我正在将 CATiledLayer 实现到 UIScrollView 中。在CATiledLayer中，我有一个绘制图层的函数，如下所示：
- (void)drawLayer:(CALayer *)layer inContext:(CGContextRef)ctx {
CGContextTranslateCTM(ctx, 0.0f, 0.0f);
CGContextScaleCTM(ctx, 1.0f, -1.0f);
CGRect box = CGContextGetClipBoundingBox(ctx);
NSData *data = [NSData dataWithContentsOfURL:[NSURL URLWithString:@"urlhere"]];
UIImage *image = [[UIImage alloc] initWithData:data];
CGContextDrawImage(ctx, box, [image CGImage]);
[image release];
[data release];
}
问题是，当每个图块下载时，它会阻止其他图块的下载。我非常希望这些图块能够并行下载。特别是它会阻止我无法控制的另一个 UI 元素的下载。
基本上，我只需要知道如何在 CATiledLayer 绘图消息中异步下载数据。
I am implementing a CATiledLayer into a UIScrollView. In the CATiledLayer, I have a function to draw the layers like so:
- (void)drawLayer:(CALayer *)layer inContext:(CGContextRef)ctx {
CGContextTranslateCTM(ctx, 0.0f, 0.0f);
CGContextScaleCTM(ctx, 1.0f, -1.0f);
CGRect box = CGContextGetClipBoundingBox(ctx);
NSData *data = [NSData dataWithContentsOfURL:[NSURL URLWithString:@"urlhere"]];
UIImage *image = [[UIImage alloc] initWithData:data];
CGContextDrawImage(ctx, box, [image CGImage]);
[image release];
[data release];
}
The problem is that when each tile is downloading it blocks the downloads of other tiles. I would very much prefer if these tiles were downloaded in parallel. In particular it blocks the downloads of another UI element that I am not in control over.
Basically, I just need to know how to download data asynchronously in a CATiledLayer drawing message.
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您可以使用 NSURLConnection 之类的工具异步下载数据，就像在任何其他情况下一样。下载完成后，告诉图层重新绘制，然后调用 -drawLayer:inContext: 此时您只需抓取已下载的图像。换句话说，不要在 -drawLayer 中下载数据，也不要使用 -dataWithContentsOfURL，它是同步的，默认情况下会阻塞。
You download the data asynchronously as you would in any other situation using something like NSURLConnection. When the download has completed, tell the layer to re-draw which will then call -drawLayer:inContext: at which point you just grab the image that was downloaded. In other words, don't download your data in -drawLayer and don't use -dataWithContentsOfURL which is synchronous and blocks by default.