Fastest way to write a large file on the iPhone?

Question

This app i'm working on allows the user to take pictures, and saves them locally (a small thumbnail image via Core Data, and the full-size image in the documents directory). I'm finding that writing the image file to the documents directory takes a long time, though -- 8 seconds on my iPhone 3GS, even longer on my iPhone 3G and first-gen iPod touch. I write the file this way:

[imgData writeToFile:imagePath atomically:YES];

... is there a faster way to do this? The iPhone's camera app seems to write the images to the filesystem very quickly. I could do the writing in a thread, but i'm concerned about the user possibly quitting my app before the thread finishes.

Answer 1

• A closely related question has been asked before, and the general opinion is that the iPhone's camera app uses undocumented internal API calls. I'm personally not sure if this is true, I think it's more likely that the iPhone app can persist in the background until the image is saved, a "commodity" not yet available to third party apps on non-jailbroken devices.
• Perhaps you should try indeed using a thread to save your image, but in a more data-oriented way, in byte chunks. This way, if the user presses the home button, in your - (void) applicationWillTerminate(UIApplication *)application method from the app's delegate, you could finalize the process of data saving to disk. This will only buy you an extra 5 seconds, though, but it's better than nothing at all. Similar recommendations have been given on saving a text file. Hope this helps, best of luck!