CODEWITHSUNDEEP
iosswift3xcode8
user2596590
user2596590

Reputation: 29

IOS App keeps Images in Memory

I have an app that has two view controllers with images

when I launch the app the memory increases and when I then segue to the other view controller and load the 2nd image ( I have a button to do this ) the memory goes up again.. this is what I would have expected..

However, when I dismiss the 2nd VC controller or removing the image in the 2nd VC via a button, and then dismiss the controller , the memory never goes down.

why is this, with an app with lots of images it could get large.. how do I release the memory of the 2nd VC or at least the memory of the 2nd image.

Im looking at memory under debug navigator in Xcode 8, when running the app.

xcode project can be found here , very simple

Upvotes: 1

Views: 923

Answers (1)

Rob
Rob

Reputation: 437552

iOS will cache images. The documentation for UIImage(named:) says:

Discussion

This method looks in the system caches for an image object with the specified name and returns the variant of that image that is best suited for the main screen. If a matching image object is not already in the cache, this method locates and loads the image data from disk or from an available asset catalog, and then returns the resulting object.

The system may purge cached image data at any time to free up memory. Purging occurs only for images that are in the cache but are not currently being used...

Special Considerations

If you have an image file that will only be displayed once and wish to ensure that it does not get added to the system’s cache, you should instead create your image using imageWithContentsOfFile:. This will keep your single-use image out of the system image cache, potentially improving the memory use characteristics of your app.

Note, you don't control when this cache is freed. The OS does that as it sees fit (and generally in response to memory pressure).

Bottom line, we often don't worry about inherent caching by UIImage and simply ensure the app doesn't have its own memory issues, e.g. make sure deinit is getting called and/or use the "Debug Memory Graph" feature in Xcode to watch memory graph. Or if you want, programmatically set the image using UIImage(contentsOfFile:).

Upvotes: 1

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