saving array of images with UIImagePNGRepresentation memory warning swift -

i'm capturing randomly-sized/shaped sections of uiview , saving disk using uiimagepngrepresentation. files save expected, when run on device, dreaded "received memory warning", though i'm doing saving files in loop , not displaying them:

uigraphicsbeginimagecontextwithoptions(bbox.size, false, 0) cgcontextsetfillcolorwithcolor(uigraphicsgetcurrentcontext(), uicolor(red: 1.0, green: 0.0, blue: 0.0, alpha: 0.25).cgcolor) cgcontextaddrect(uigraphicsgetcurrentcontext(), cgrectmake(0, 0, bbox.width, bbox.height)) cgcontextfillpath(uigraphicsgetcurrentcontext())  let strokeimage = uigraphicsgetimagefromcurrentimagecontext() let strokefile = "stroke_\(strokebezierarraymemory.count).png" let datapng = uiimagepngrepresentation(strokeimage) let fileurl = folderurl!.urlbyappendingpathcomponent(strokefile)  //println("\(fileurl)") if (datapng.writetourl(fileurl, options: .atomicwrite, error: &error) ) {   //println ("wrote \(fileurl)") } else {   print (error) } 

i've seen similar posts, no answers solve problem. this post suggests using avfoundation, i'm hoping can stick uiimagepngrepresentation.

i tried wrapping nsdata part of code in autoreleasepool closure no avail:

autoreleasepool({ () -> () in   let strokefile = "stroke_\(strokebezierarraymemory.count).png"   let data = uiimagepngrepresentation(strokeimage)   let fileurl = folderurl!.urlbyappendingpathcomponent(strokefile)  //println("\(fileurl)")   if (data.writetourl(fileurl, options: .atomicwrite, error: &error) ) {     //println ("wrote \(fileurl)")   } else {     print (error)   } }) 

is there way force nsdata release each datapng once written disk?