Question

On my quest to reduce memory usage, another question.
I see that UIImage and CGImage might be candidates for high memory usage in my app.
Wherever I use a UIImage, I try to wrap it in a using block to have it Dispose()‘d as soon as possible.

However, often the UIImage ends up in a UIImageView.Image property.
If I remove the UIIImageView from its Superview, am I supposed to Dispose() the Image property before and set it to null or is this wasted typing?

Answer 1

am I supposed to Dispose() the Image property

Quick answer: No.

Long answer:

The UIImageView.Image property, image selector, is retained. Even if you dispose it (from the managed side) the native retainCount (Objective-C is reference counted) of the UIImage will still be higher than 0 and the (native side of the) UIImage won’t be freed.

When you dispose the UIImageView it will release the UIImage it use (Apple’s Objective-C code) and, if the retainCount reach 0, it will be natively freed.

If there’s a large delay between when you stop needing the UIImage and the time you dispose of the UIImageView then you might want to set UIImageView.Image to null. That will release (in the ObjC way, i.e. drop its retainCount by one) the UIImage and, if it’s not used elsewhere, it will be (natively) freed.

Note that, if the UIImageView is not disposed, then setting its Image property to another UIImage will have the same result (the old one’s will be released).