How to detect total available/free disk space on the iPhone/iPad device?

Question

I\'m looking for a better way to detect available/free disk space on the iPhone/iPad device programmatically.
Currently I\'m using the NSFileManager to detect the disk s

Answer 1

Update with a new accurate API to get available size on disk available in iOS11. Here is the description for the new API resource key:

#if os(OSX) || os(iOS)
/// Total available capacity in bytes for "Important" resources, including space expected to be cleared by purging non-essential and cached resources. "Important" means something that the user or application clearly expects to be present on the local system, but is ultimately replaceable. This would include items that the user has explicitly requested via the UI, and resources that an application requires in order to provide functionality.
/// Examples: A video that the user has explicitly requested to watch but has not yet finished watching or an audio file that the user has requested to download.
/// This value should not be used in determining if there is room for an irreplaceable resource. In the case of irreplaceable resources, always attempt to save the resource regardless of available capacity and handle failure as gracefully as possible.
@available(OSX 10.13, iOS 11.0, *) @available(tvOS, unavailable) @available(watchOS, unavailable)
public var volumeAvailableCapacityFor Usage: Int64? { return _get(.volumeAvailableCapacityForImportantUsageKey) }
#endif

I cross compared the results from key "FileAttributeKey.systemFreeSize" and key "URLResourceKey.volumeAvailableCapacityForImportantUsageKey" and found the results returned form "volumeAvailableCapacityForImportantUsageKey" exactly matches the available storage shown on UI. Here is the swift implementation:

class var freeDiskSpaceInBytesImportant:Int64 {
    get {
        do {
            return try URL(fileURLWithPath: NSHomeDirectory() as String).resourceValues(forKeys: [URLResourceKey.volumeAvailableCapacityForImportantUsageKey]).volumeAvailableCapacityForImportantUsage!
        } catch {
            return 0
        }
    }
}