Prevent Spotify Using 3G on iPhone

In the Spotify iPhone application, there is a manual setting to turn offline mode on or off. Ideally there would be a feature that automatically switches to offline mode as soon as a wifi connection is left and returns to online mode when connected again. Is there another way to achieve this goal?

• How can I move or replicate my Apple iTunes Apple Music library to Spotify?
• Set Spotify as the source of song titles instead of iTunes
• Spotify Premium account price on the App Store
• Can I run Spotify by pressing the F8 button instead of iTunes?
• Ignore the “prevent sleep” prompt from a specific application

• Is there an easy way to temporarily grant networking access to a single application?
• Bluetooth speaker controls don’t work with Spotify on macOS
• The My Spotify application will not open, cannot be deleted, and will not be forced to quit macOS
• Xcode wants to access DeviceManager in your keyfob and tells me to add Spotify accessibility
• Run iTunes viewer out of Spotify output or built-in microphone?
• Opening Skype causes Spotify to pause playback from iOS 8.0.2
• Is there any way to make offline content of third party music apps on iPhone like iPod / Music?
• Can Spotify be interrupted when a Skype call is made, similar to how iTunes does it?