How to completely remove Realm database from iOS?

To completely delete the Realm file from disk and start from scratch, it's simply a matter of using NSFileManager to manually delete it.

For example, to delete the default Realm file:

NSFileManager.defaultManager().removeItemAtURL(Realm.Configuration.defaultConfiguration.fileURL!)

If you want to preserve the Realm file, but completely empty it of objects, you can call deleteAll() to do so:

let realm = try! Realm()
try! realm.write {
  realm.deleteAll()
}

Update: I feel I neglected to mention this in my original answer. If you choose to delete the Realm file from disk, you must do so before you've opened it on any threads in your app. Once it's opened, Realm will internally cache a reference to it, which won't be released even if the file is deleted.

If you absolutely do need to open the Realm file to check its contents before deletion, you can enclose it in an autoreleasepool to do this.

This is how to do in swift 4.1:

FileManager.default.removeItem(at:Realm.Configuration.defaultConfiguration.fileURL!)