Previewing Files In-App in Rork — calling Quick Look safely from Expo

Call iOS Quick Look through a bridge module

QLPreviewController is a UIViewController, so present it from your Expo native module on top of the current top screen. The data source is a thin thing that just returns the item to preview.

import QuickLook
 
final class PreviewBridge: NSObject, QLPreviewControllerDataSource {
  private var url: URL!
 
  func present(path: String, from vc: UIViewController) {
    self.url = URL(fileURLWithPath: path)
    let preview = QLPreviewController()
    preview.dataSource = self
    vc.present(preview, animated: true)
  }
 
  func numberOfPreviewItems(in controller: QLPreviewController) -> Int { 1 }
 
  func previewController(_ controller: QLPreviewController,
                         previewItemAt index: Int) -> QLPreviewItem {
    return url as QLPreviewItem
  }
}

From JavaScript, make it a call site that just passes the downloaded local path.

import { ensureLocalCopy } from './downloadForPreview';
import QuickLookPreview from './QuickLookBridge'; // native module
 
export async function openPreview(remoteUrl: string, filename: string) {
  const localPath = await ensureLocalCopy(remoteUrl, filename);
  // The implementation passes a path with file:// stripped on iOS
  await QuickLookPreview.present(localPath.replace('file://', ''));
}

On Android, substitute with FileProvider and ACTION_VIEW

Android has no Quick Look. Instead, build a safe content URI with FileProvider and hand it off via Intent.ACTION_VIEW. If you insist on a full-screen in-app view, using a built-in viewer for PDFs only and delegating the rest to external apps turned out to be the practical compromise.

fun openWithViewer(context: Context, file: File, mime: String) {
  val uri = FileProvider.getUriForFile(
    context, "${context.packageName}.fileprovider", file
  )
  val intent = Intent(Intent.ACTION_VIEW).apply {
    setDataAndType(uri, mime)
    addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION)
  }
  // Guard against crashing when no app can handle it
  if (intent.resolveActivity(context.packageManager) != null) {
    context.startActivity(intent)
  } else {
    // Fallback: a chooser or a built-in PDF viewer
  }
}

Keep the JS openPreview under the same name and branch so iOS calls Quick Look and Android calls this Intent. Folding it into one call site means your screen code never has to think about platform differences.

How to handle the share and print buttons

Quick Look shows share and print buttons in the top right by default. This needs a design decision.

When you want to suppress sharing, handle it through the QLPreviewController delegate that controls edit/share capability rather than the QLPreviewItem. Complete exfiltration prevention is hard given how the OS works, so it's safest to design on the assumption that "screenshots can still be taken" and not over-promise. In my case the line is: free confirmation previews allow share; paid content switches to a built-in viewer and skips Quick Look entirely.

Large files and cleanup after closing

Download a tens-of-MB PDF and then open it, and you get a silent wait. Don't open the preview while downloading — show progress, and users feel more at ease. expo-file-system's createDownloadResumable gives you a progress callback.

Cleanup after closing is easy to forget. Files dropped into the cache pile up if you leave them. My policy is "keep the most recently opened ones, and sweep caches untouched for a while at startup." Anything under cacheDirectory the OS will clear when it has to, but setting your own ceiling avoids storage pressure.

When a file can be viewed to completion inside the app, the user keeps working without losing context. Quick Look itself is a few lines to call, but it only becomes a viewing path you can rely on once you include remote pre-downloading, the Android substitute, share gating, and cleanup. I hope it helps anyone working on the same implementation.