Patterns - Errors(App error and incompatible state error)

출처 : http://www.google.com/design/spec/patterns/errors.html#errors-user-input-errors

     App errors

App errors occur independent of user input.

General app error

When an error occurs, an app should display loading indicators until the error message appears.

Features not available may be represented in the UI. Not every error requires a new component to pop up.

If possible, give your user an action that will help them address the error.

Alert dialog: app feedback about an error that is blocking normal operation  

Snackbar: app feedback about a peripheral error. Snackbars are transient, don't use them for critical, persistent, or bulk errors.

Sync error/failure to load

When sync is down or content has failed to load, the user should be able to interact with as much of the rest of the app as possible.

Empty state for the screen/content failing to load.

Container/component specific error with action.

Connectivity

When connectivity is down, the user should be able to interact with as much of the rest of the app as possible.

If appropriate, present a link to help a user accomplish their task. Only offer links that you can actually support. For example, don't offer an option like "Try again" in cases where you can detect that the operation will fail.

Snackbar with action to retry

Empty state for a screen only available online

Incompatible state errors

Incompatible state errors occur when users attempt to run operations that conflict, such as making a call while in airplane mode or taking a screenshot from a restricted work account. Help prevent users from putting themselves into these situations by clearly communicating the states they are selecting and the implications for the rest of their experience. When these errors are triggered, do not imply that they are the user’s fault.

General incompatibility

Clarify the reason for and origination of the error.  

For example, screenshots and premium features are not allowed while in a restricted mode.

Snackbar + Special mode indicator

Offline by choice

Display an unobtrusive, persistent indicator when users are offline but try to do tasks that require being online.

Examples:

• Placing a call while in airplane mode
• Music availability while offline

Snackbar

Indicator that the device has been placed into airplane mode.

Permission requested

If your app requires user permission before proceeding with an action, include the permission request in the app flow instead of treating it as an error.

If permissions are necessary before the first run of an app, consider including them into your app’s first-run experience.

Examples:

• An app’s permissions have changed.
• In-app purchases have been disabled.

Dialog