Don't make people sit around staring at a static screen, waiting for your app to load content or perform lengthy data processing operations. Use activity indicators and progress bars to let people know your app isn't stalled, and to give them some idea of how long they will be waiting. Let's start the topic of progress indicators. With an activity indicator is that animated spinning wheel you see when the content is loading or the task is being performed. An activity indicator shows that a task or process is progressing and activity indicator spins while an unquantifiable task such as the loading or synchronizing complex data is being performed. It disappears when the task completes.
Activity indicators are non interactive. The activity indicator in this example also has a text label and pointing that out. Because it can be just a spinner, like in this example. Anyways, using the activity indicator in the toolbar, or in the main view to show that processing is occurring, without suggesting when it will finish. That's right. Activity indicator can also be placed in the toolbar.
Don't display a stationary activity indicator. Users associate a stationary activity indicator with a stall process. So keep it spinning so they know something's happening. If it's helpful, provide useful information while waiting for a task to complete. Include a label with an activity indicator to give extra context. Try to be more specific than just using fact terms like loading.
Customize an activity indicator to harmonize with the view it's in if appropriate, coordinate the size and color If an activity indicator with the background of the views in as we've seen this example, a background can be added to the activity indicator. And that's just one example. Favorite progress bars over activity indicators. If activity is quantifiable use a progress bar instead of an activity indicator so people can better go watch what's happening and how long it will take. not mentioned in the iOS guidelines, but it's okay to use some custom spinners. Make sure they match your style though and that they're understandable.
You can always stay safe with the standard one though.