# Passing Data and Deep Links — Flutter

Source: https://www.skillbyai.com/en/flutter/n-deeplinks

> Arguments, query parameters and platform links.

## Getting data to the next screen

Pass small, serialisable data such as IDs through the **path or query string** (`/products/42?tab=reviews`) so the screen can rebuild itself from the URL alone - this is what makes refresh on the web and deep links work. Load the full object inside the destination screen. go_router also supports an `extra` object, but it is not part of the URL and is lost on a web refresh or a cold-start deep link. **Deep links** open the app from outside: Android **App Links** need an intent filter and a `assetlinks.json` file on your domain, and iOS **Universal Links** need the Associated Domains entitlement and an `apple-app-site-association` file. With a router configured, Flutter passes the incoming path to it; check the Flutter deep linking guide for current setup steps.

## Reading path and query parameters

Inside a GoRoute builder (go_router 10+ style).

```dart
GoRoute(
  path: '/products/:id',
  builder: (context, state) {
    final id = state.pathParameters['id']!;
    final tab = state.uri.queryParameters['tab'] ?? 'details';
    return ProductPage(id: id, initialTab: tab);
  },
);

// a deep link such as https://shop.example.com/products/42?tab=reviews
// opens ProductPage(id: '42', initialTab: 'reviews')
```

## Test links from the command line

On Android you can fire a link with adb shell am start -a android.intent.action.VIEW -d "<url>"; on the iOS simulator use xcrun simctl openurl booted "<url>".

**Quiz:** Why prefer passing an ID in the URL over passing a whole object with extra?

- [x] The screen can be rebuilt from the URL alone, so refreshes and deep links work
- [ ] Objects cannot be passed in Dart
- [ ] URLs are encrypted
- [ ] extra is slower to type

*Answer:* The screen can be rebuilt from the URL alone, so refreshes and deep links work. Data that is not in the URL is lost when the app is opened from a link.