Dart compile errorFlutter: “The argument type ‘String’ can’t be assigned to the parameter type ‘Uri’”

Why a String is rejected, and the fix

1. 01

   Code written for package:http before 0.13

   “All APIs which previously allowed a String or Uri to be passed now require a Uri.” pub.dev, package:http 0.13.0 changelog

   get, post, put, delete and the Client methods all take a Uri now. Convert the string once, at the call.

   import 'package:http/http.dart' as http;
   
   final response = await http.get(Uri.parse('https://api.example.com/items'));

2. 02

   A URL built by joining strings

   String concatenation breaks on spaces and special characters in query values. Uri.https builds the URL from parts and encodes the query for you; use Uri.http for plain http, such as a local server. Pass the bare host (api.example.com), not https://api.example.com.

   final uri = Uri.https('api.example.com', '/search', {
     'q': query,
     'page': '$page',
   });
   final response = await http.get(uri);

3. 03

   url_launcher and WebView calls

   The same error comes from launchUrl and canLaunchUrl in url_launcher (the old launch took a String) and from WebViewController.loadRequest. Parse the string first.

   await launchUrl(Uri.parse(url));
   controller.loadRequest(Uri.parse(url));

4. 04

   A malformed URL string

   Uri.parse throws a FormatException for a string that isn’t a valid URI. Use Uri.tryParse for user input, which returns null instead of throwing.

   final uri = Uri.tryParse(input);
   if (uri == null || !uri.hasScheme) {
     // show a validation error
   }

Checked against the vendor’s docs on November 8, 2026: pub.dev: package:http changelog (0.13.0); Dart API: Uri.parse.

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