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Files, Assets, HTML

Local Files

Section titled “Local Files”
await controller.loadFile('/Users/me/Documents/page.html');

Platform behavior:

Platform Behavior
Android Uses file URL loading. AndroidLoadFileParams can add headers.
iOS/macOS Uses WebKit local file loading. WebKitLoadFileParams controls read access scope.
Windows Maps the file’s directory to a virtual HTTPS host.
Linux Loads the absolute file through WebKitGTK.
OHOS Enables file access and loads the file URL.
Web Unsupported; browsers do not allow arbitrary file reads from a hosted app.

Android File Headers

Section titled “Android File Headers”
await controller.platform.loadFileWithParams(
  AndroidLoadFileParams(
    absoluteFilePath: '/sdcard/Download/page.html',
    headers: const <String, String>{'X-Source': 'app'},
  ),
);

WebKit Read Access

Section titled “WebKit Read Access”
await controller.platform.loadFileWithParams(
  WebKitLoadFileParams(
    absoluteFilePath: '/Users/me/site/index.html',
    readAccessPath: '/Users/me/site',
  ),
);

readAccessPath must include any images, scripts, and styles referenced by the HTML file.

Flutter Assets

Section titled “Flutter Assets”

Declare the asset:

flutter:
  assets:
    - assets/help/index.html

Load it:

await controller.loadFlutterAsset('assets/help/index.html');

On Windows, the implementation maps the asset directory to an internal HTTPS host. On web, it resolves the asset under the app’s generated assets/ path.

Inline HTML

Section titled “Inline HTML”
await controller.loadHtmlString(
  '<html><body><a href="details.html">Details</a></body></html>',
  baseUrl: 'https://docs.example.com/help/',
);

Use baseUrl when the document contains relative URLs.

Custom Requests

Section titled “Custom Requests”
await controller.loadRequest(
  Uri.parse('https://api.example.com/form'),
  method: LoadRequestMethod.post,
  headers: const <String, String>{'Content-Type': 'application/json'},
  body: Uint8List.fromList(utf8.encode('{"ok":true}')),
);

Check platform support before relying on custom requests:

Platform Notes
Android POST with custom headers is not supported by Android WebView postUrl.
OHOS POST with custom headers is not supported by ArkWeb postUrl; webview_all_ohos throws UnsupportedError.
Web Non-simple requests use fetch and require CORS approval from the server.
Windows/Linux/iOS/macOS Support method, headers, and body through native request APIs.

Recommended Fallback for Unsupported POST Headers

Section titled “Recommended Fallback for Unsupported POST Headers”

When a platform cannot submit a POST with custom headers directly, send the request with your app’s HTTP client and load the resulting HTML:

final response = await http.post(
  Uri.parse('https://api.example.com/form'),
  headers: const <String, String>{'Authorization': 'Bearer token'},
  body: '{"ok":true}',
);


await controller.loadHtmlString(
  response.body,
  baseUrl: 'https://api.example.com/form',
);

This fallback is appropriate for HTML responses. It is not equivalent to browser navigation for cookies, redirects, service workers, or streaming responses.