1

我有以下方法，它需要一些CAShapeLayers并将它们转换为UIImage. 用于单元格UIImage中的 a UITableView（很像从您的一个库中选择照片时的照片应用程序）。这个方法是从一个GCD块中调用的：

-(UIImage*) imageAtIndex:(NSUInteger)index
{
    Graphic *graphic = [[Graphic graphicWithType:index]retain];

    CALayer *layer = [[CALayer alloc] init];
    layer.bounds = CGRectMake(0,0, graphic.size.width, graphic.size.height);
    layer.shouldRasterize = YES;
    layer.anchorPoint = CGPointZero;
    layer.position = CGPointMake(0, 0);

    for (int i = 0; i < [graphic.shapeLayers count]; i++)
    {
        [layer addSublayer:[graphic.shapeLayers objectAtIndex:i]];
    }

    CGFloat largestDimension = MAX(graphic.size.width, graphic.size.height);
    CGFloat maxDimension = self.thumbnailDimension;
    CGFloat multiplicationFactor = maxDimension / largestDimension;
    CGSize graphicThumbnailSize = CGSizeMake(multiplicationFactor * graphic.size.width, multiplicationFactor * graphic.size.height);

    layer.sublayerTransform = CATransform3DScale(layer.sublayerTransform, graphicThumbnailSize.width / graphic.size.width, graphicThumbnailSize.height / graphic.size.height, 1);
    layer.bounds = CGRectMake(0,0, graphicThumbnailSize.width, graphicThumbnailSize.height);

    UIGraphicsBeginImageContextWithOptions(layer.bounds.size, NO, 0);
    [layer renderInContext:UIGraphicsGetCurrentContext()];
    UIImage *image = [UIGraphicsGetImageFromCurrentImageContext() retain];
    UIGraphicsEndImageContext();

    [layer release];
    [graphic release];

    return [image autorelease];
}

无论出于何种原因，当我滚动UITableView并加载图像时，它有点口吃。我知道GCD代码很好，因为它以前工作过，所以看起来这段代码中的某些东西导致了口吃。有谁知道那可能是什么？不是CAAnimation线程安全的吗？或者有没有人知道更好的方法来获取一堆CAShapeLayers并将它们转换成一个UIImage？

4

1 回答 1

1

最后我相信：

[layer renderInContext:UIGraphicsGetCurrentContext()];

无法在单独的线程上完成，因此我必须执行以下操作：

UIGraphicsBeginImageContextWithOptions(imageSize, NO, 0);
CGContextRef context = UIGraphicsGetCurrentContext();
//draw the mutable paths of the CAShapeLayers to the context
UIImage *image = [UIGraphicsGetImageFromCurrentImageContext() retain];
UIGraphicsEndImageContext();

在WWDC2012视频“Building Concurrent User Interfaces on iOS”中有一个很好的例子（我学会了这样做）

于 2012-12-25T19:19:15.553 回答