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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, each controller maps the canonical asset directory to a private randomized HTTPS host with cross-origin access denied. Mappings are replaced or cleared as navigation changes. Linux requires absolute file paths and canonicalizes them before loading. Both implementations reject traversal and symlink escapes outside the Flutter asset bundle. On web, assets resolve 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, require CORS approval, preserve binary response bytes, and use the final redirect URL as the logical URL.
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.