Ensure that your apps are useable by the widest possible audience
Accessibility refers to the concept of designing app user interfaces that work well operating system display- and input-assistance features such as large type, high contrast, zoom in, screen reading (text-to-speech), visual or haptic feedback cues, and alternative input methods.
To implement the guidelines in this document, use the APIs provided by each platform:
Follow these tips to ensure that your apps are accessible to the widest audience possible. Check out the Android Accessibility Testing Checklist and Apple's Accessibility page for additional information.
Support large fonts and high contrast
Avoid hardcoding control dimensions and, instead, prefer layouts that can resize to accommodate larger font sizes. Test color schemes in high-contrast mode to ensure that they are readable.
Make the user interface self-describing
Tag all the elements of your user-interface with descriptive text and hints that are compatible with the screen reading APIs on each platform.
Ensure that images and icons have an alternate text description
Images and icons that are part of the application user interface (such as buttons or indicators of status, for example) should be tagged with an accessible description.
Design the visual tree with accessible navigation in mind
Use appropriate layout controls or APIs so that navigating between controls using alternate input methods follows the same logical flow as using the touch screen.
Exclude unnecessary elements from screen readers (decorative images or labels for fields that are already accessible, for example).
Don't rely on audio or color cues alone
Avoid situations where the sole indication of progress, completion, or some other state is a sound or color-change. Either design the user interface to include clear visual cues (with sound and color for reinforcement only), or add specific accessibility indicators.
When choosing colors, try to avoid a palette that is hard to distinguish for users with color blindness.
Captioning for video, text for audio
Provide captions for video content, and a readable script for audio content. It's also helpful to provide controls that adjust the speed of audio or video content, and ensure that volume and play/pause buttons are easy to find and use.
Accessibility descriptions can (and should) be localized where the application supports multiple languages.