Files, Assets, HTML

HTML file inputs

<input type="file"> is a page-initiated picker, not loadFile. Android uses the built-in Photo Picker / content chooser / camera path. iOS uses WKWebView’s system picker. macOS uses NSOpenPanel. Windows, Linux, and Web use the engine or browser dialog. See Permissions for host-app manifest and Info.plist keys.

Manual checks after a page load:

<input type="file" accept="image/*" multiple> opens the Photo Picker or system picker, allows more than one image, and canceling lets you tap the control again.
<input type="file"> without accept can pick an arbitrary file such as a PDF.
<input type="file" accept="image/*" capture> asks for camera permission and then opens the camera. Denying permission or backing out of the camera must not freeze the input.

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.
Enables file access and loads the file URL.
Unsupported; browsers do not allow arbitrary file reads from a hosted app.

Android File Headers

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

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

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

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

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`.
Web	Non-simple requests use `fetch`, require CORS approval, preserve binary response bytes, and use the final redirect URL as the logical URL.
Other native platforms	Support method, headers, and body through native request APIs.