Ios drawMapRect上下文+;中央大调度
我有这个功能:Ios drawMapRect上下文+;中央大调度,ios,objective-c,mapkit,grand-central-dispatch,Ios,Objective C,Mapkit,Grand Central Dispatch,我有这个功能: - (void)drawMapRect:(MKMapRect)mapRect zoomScale:(MKZoomScale)zoomScale inContext:(CGContextRef)context { TileOverlay *tileOverlay = (TileOverlay *)self.overlay; NSArray *tilesInRect = [tileOverlay tilesInMapRect:mapRect zoomScale:zoo
- (void)drawMapRect:(MKMapRect)mapRect zoomScale:(MKZoomScale)zoomScale inContext:(CGContextRef)context
{
TileOverlay *tileOverlay = (TileOverlay *)self.overlay;
NSArray *tilesInRect = [tileOverlay tilesInMapRect:mapRect zoomScale:zoomScale];
CGContextSetAlpha(context, tileAlpha);
for (ImageTile *tile in tilesInRect)
{
__block UIImage * image;
CGRect rect = [self rectForMapRect:tile.frame];
NSString *path = [[NSString alloc] initWithFormat:@".../%@.png", tile.imagePath];
NSLog(@"Loading tile from URL %@", path);
image =[UIImage imageWithData: [NSData dataWithContentsOfURL:[NSURL URLWithString: path]]];
CGContextSaveGState(context);
CGContextTranslateCTM(context, CGRectGetMinX(rect), CGRectGetMinY(rect));
CGContextScaleCTM(context, 1/zoomScale, 1/zoomScale);
CGContextTranslateCTM(context, 0, image.size.height);
CGContextScaleCTM(context, 1, -1);
CGContextDrawImage(context, CGRectMake(0, 0, image.size.width, image.size.height), [image CGImage]);
CGContextRestoreGState(context);
}
}
正如您所知,dataWithContentsOfURL
将阻塞线程,直到完成。我想将图像加载块添加到GCD
部分
我试着这样做:
- (void)drawMapRect:(MKMapRect)mapRect zoomScale:(MKZoomScale)zoomScale inContext:(CGContextRef)context
{
TileOverlay *tileOverlay = (TileOverlay *)self.overlay;
NSArray *tilesInRect = [tileOverlay tilesInMapRect:mapRect zoomScale:zoomScale];
CGContextSetAlpha(context, tileAlpha);
for (ImageTile *tile in tilesInRect)
{
__block UIImage * image;
CGRect rect = [self rectForMapRect:tile.frame];
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW,0), ^{
NSString *path = [[NSString alloc] initWithFormat:@".../%@.png", tile.imagePath];
NSLog(@"Loading tile from URL %@", path);
image =[UIImage imageWithData: [NSData dataWithContentsOfURL:[NSURL URLWithString: path]]];
CGContextSaveGState(context);
CGContextTranslateCTM(context, CGRectGetMinX(rect), CGRectGetMinY(rect));
CGContextScaleCTM(context, 1/zoomScale, 1/zoomScale);
CGContextTranslateCTM(context, 0, image.size.height);
CGContextScaleCTM(context, 1, -1);
CGContextDrawImage(context, CGRectMake(0, 0, image.size.width, image.size.height), [image CGImage]);
CGContextRestoreGState(context);
});
}
}
但我有上下文错误。请帮我拿这东西。
如何在GCD块中使用上下文操作?我的第一个注意事项是MKOVERYVIEW已折旧。您应该考虑切换到MKOFLADRIENDER。 在任何情况下,都不应该从-draw_u_;方法中使用GCD。这包括MKOverlayView-drawMapRect:zoomScale:inContext:以及UIView-drawMapRect:。相反,您应该将NSOperationQueue与-canDrawMapRect:zoomScale:zoomScale和setNeedsDisplayinPrect:结合使用 下面是一些sudo代码:
- (BOOL)canDrawMapRect:(MKMapRect)mapRect zoomScale:(MKZoomScale)zoomScale
{
BOOL hasAtLeastOneTile = NO;
TileOverlay *tileOverlay = (TileOverlay *)self.overlay;
NSArray *tilesInRect = [tileOverlay tilesInMapRect:mapRect zoomScale:zoomScale];
for (ImageTile *tile in tilesInRect) {
if ([tile isAvailable]) {
hasAtLeastOneTile = hasAtLeastOneTile || YES;
} else {
// Add operation to NSOperationQueue to fetch tile
__weak MKOverlayView *weakOverlay = self; // Weak ref to prevent retain cycles
NSOperation *op = [NSBlockOperation blockOperationWithBlock: ^{
//TODO: Load Tile
[weakOverlay setNeedsDisplayInMapRect:mapRect];
}];
[self.operationQueue addOperation:op];
}
}
return hasAtLeastOneTile;
}
然后在你的-drawMapRect:zoomScale:inContext中:你绘制可用的分幅,并跳过不可用的分幅。你不能在主(UI)线程之外绘制,但我可以并行线程下载,然后更新,是吗?是的,你将需要发送到主线程非常有用,谢谢。如果可能的话,请回答一些愚蠢的问题=)我需要检查drawMapRect中是否有磁砖,是吗?所以我需要一些图像阵列(或地图)与所有瓷砖?还有其他问题:如果tile不可用并且现在已经下载,它会在drawMapRect中自动更新吗?谢谢你的时间,你应该已经有了任何你想画的东西。这通常意味着您将平铺存储在某种类型的数据结构中,例如NSMutableDictionary。此外,当您调用-setNeedsDisplayinPrect:,它将触发您通过调用-drawMapRect:zoomScale:inContext:指定的区域的重绘。您不应该直接调用-drawMapRect:zoomScale:inContext:yourself。