Part 1 — ListViews

• Shrink wrapping ListView.builder or using NeverScrollableScrollPhysics.
• Letting every item in the list determine height on its own.
• Wrapping a ListView into a Padding widget.
• Using wrong scroll physics for different platforms.
• Adding keys to every list item and expecting that it will improve the scrolling performance.
• Not using restorationId.

Part 2 — Images

• Large image assets.
• Not using WebP assets.
• Using the Opacity widget when not needed.
• Not precaching image assets.
• Not caching network images.
• Not optimizing SVG assets.

Part 3 — i18n

• Using different string entries to make a single sentence by concatenating.
• Ignoring plurals or writing some custom logic to handle it.
• Manually formatting date and time, hardcoding names of months, days of week.
• Concatenating currency and price strings.
• Using fonts that support only Latin script.

Part 4 — OAuth

• Using WebView to handle auth flow.
• Storing access tokens in a non-secure storage.
• Racing refreshing sessions when the refresh token is allowed to be used only once.
• Bundling client secrets in the application.