Monotouch: Generating UIImage from PDF leaking entire document size - pdf

Question

In a Monotouch application the following code converts a page from a PDF document to a UIImage. It works, but it doesn't correctly dispose the PDF document.
public class KillerLeak
{
public static void RunOnce()
{
using (CGPDFDocument doc = CGPDFDocument.FromFile("DMSWorkbook.pdf"))
{
Console.WriteLine("Opened: pages={0}", doc.Pages);
UIImage img = GetThumbImage(doc, 1000, 1);
img.Dispose();
}
GC.Collect(GC.MaxGeneration);
GC.WaitForPendingFinalizers();
}
private static UIImage GetThumbImage(CGPDFDocument document, float thumbContentSize, int pageNumber)
{
if ((pageNumber <= 0) || (pageNumber > document.Pages)) {
return null;
}
// Calc page view size
SizeF pageSize = new SizeF(768, 1024);
if (pageSize.Width % 2 > 0) {
pageSize.Width--;
}
if (pageSize.Height % 2 > 0) {
pageSize.Height--;
}
// Calc target size
var targetSize = new Size((int)pageSize.Width, (int)pageSize.Height);
// Draw page on CGImage
CGImage pageImage;
using (CGColorSpace rgb = CGColorSpace.CreateDeviceRGB()) {
using (CGBitmapContext context = new CGBitmapContext(null, targetSize.Width, targetSize.Height, 8, 0, rgb, CGBitmapFlags.ByteOrder32Little | CGBitmapFlags.NoneSkipFirst)) {
using (CGPDFPage pdfPage = document.GetPage(pageNumber)) {
RectangleF thumbRect = new RectangleF(0.0f, 0.0f, targetSize.Width, targetSize.Height);
context.SetFillColor(1.0f, 1.0f, 1.0f, 1.0f);
context.FillRect(thumbRect);
context.ConcatCTM(pdfPage.GetDrawingTransform(CGPDFBox.Crop, thumbRect, 0, true));
context.SetRenderingIntent(CGColorRenderingIntent.Default);
context.InterpolationQuality = CGInterpolationQuality.Default;
context.DrawPDFPage(pdfPage);
pageImage = context.ToImage();
}
}
}
UIImage result = UIImage.FromImage(pageImage);
pageImage.Dispose();
return result;
}
}
If I comment out the DrawPDFPage(...) line, the code doesn't leak. Is this a Monotouch bug or am I doing something wrong?

Answer 1

Turns out the leak is not related to Monotouch as I previously thought. The leak does not occur on IOS 5, but does leak under the next version of IOS which is still under beta. I've tested using the same code written in Monotouch and Objective-C and they both exhibit the same behavior.