In case you plan to use MiniKeePass on your iphone with key files (which I guess is highly recommended if you plan to share your kdb via Dropbox/Drive/you_name_it), pay special attention to the last line of their help page:
Using Key Files MiniKeePass can open KeePass 1.x/2.x files that use a key file instead of or in addition to a password. Steps: Load your KeePass database and key file in MiniKeePass using iTunes, Dropbox, etc. Open your KeePass file in MiniKeePass When prompted for your password you can enter a password and/or select a key file Note: MiniKeePass will automatically select your key file if it has the same filename as your KeePass file but with a .key extension.
Basically, you have to upload your data base and the key file with the same name (ie: MyDB.kdb and MyDB.key) to your_cloud_storage_service_here, and then, open both of them with MiniKeePass. Otherwise, all you will see in the Key-file screen is "None".
I learnt it the hard way and I lost 15 minutes of my life trying to import a key file with a different name than the KeePass database.
The devil is in the detail, as usual.... ;)