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Install QuickLook Plugin in Install4j macOS App Bundle

Step-by-step guide to bundle signed and notarized QuickLook plugin into Install4j macOS app. Use Copy Files action, code signing, notarization, and qlmanage for testing in JavaScript apps.

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How to install a signed and notarized QuickLook Preview Plugin into a macOS app bundle created with Install4j?

I am developing a macOS JavaScript app using Install4j, which does not natively support adding QuickLook Preview plugins to the app bundle. The advised approach is to first generate the DMG installer for the primary app, then incorporate the signed and notarized plugin. What are the detailed step-by-step instructions to achieve this?

To bundle a signed and notarized QuickLook plugin into your Install4j macOS app, add a Copy Files action in your Install4j project to target Contents/Library/QuickLook/ within the app bundle during the build process. After generating the DMG, ensure the plugin is signed with your Developer ID, submit it (and the app) for notarization via Apple’s notary service, then test by resetting QuickLook with qlmanage -r. This approach works even for JavaScript-based apps, though you might need to launch the app once post‑install for the plugin to register.

Contents

Overview of QuickLook Plugins in macOS Apps

QuickLook plugins—those .qlgenerator bundles—let users preview custom file types right in Finder with a spacebar tap. Embedding one directly into your macOS app bundle keeps everything tidy, avoiding manual installs to /Library/QuickLook/. For Install4j‑built apps (even JavaScript ones), the trick is leveraging build actions to copy the plugin into YourApp.app/Contents/Library/QuickLook/ during DMG generation.

Apple prefers this over global installs nowadays, especially for distribution. But here’s the catch: signing, notarization, and QuickLook’s picky cache can trip you up. Done right, users get instant previews without extra steps.

Prepare and Build Your QuickLook Plugin

Start with a working .qlgenerator bundle. You’ve probably already built this using Xcode or similar—it’s an app bundle with GeneratePreviewForURL, GenerateThumbnailForURL, and Info.plist declaring your UTIs.

Test it standalone first:

  • Drop it into ~/Library/QuickLook/ (user‑specific) or /Library/QuickLook/.
  • Run qlmanage -r in Terminal to reload.
  • Try qlmanage -p /path/to/yourfile.ext for a preview window.

For embedding, ensure your plugin targets the right architectures (arm64 for Apple Silicon, x86_64 for Intel). If it’s a small project, some devs duplicate source files across app and plugin targets to share code, but that’s optional. This guide on embedding covers Xcode build phases if you’re refining it there.

Once built, sign it early:
codesign --force --deep --sign "Developer ID Application: Your Name (TEAMID)" /path/to/YourPlugin.qlgenerator.
Verify with codesign -dv --verbose=4 YourPlugin.qlgenerator.

Configure Install4j for Plugin Bundling

Install4j shines here with its Copy Files action—no need for post‑DMG hacks if you set it up right. Here’s the step‑by‑step:

  1. Open your Install4j project.
  2. In the build wizard, go to Media > macOS DMG (or single bundle if not using DMG).
  3. Under Actions (pre‑ or post‑install), add a Copy Files action.
  4. Set Source to your pre‑built, signed .qlgenerator file (e.g., from a relative project path like plugins/YourPlugin.qlgenerator).
  5. Destination: @app/Contents/Library/QuickLook/ (the @app variable points to your app bundle).
  6. Ensure Overwrite is enabled for updates.

Rebuild the DMG. Boom—your QuickLook plugin lands inside the app bundle automatically. Detailed Install4j steps confirm this path works, even noting that plugins in bundles might need the app launched once to register.

Why post‑DMG tweaks if needed? If your workflow generates the primary DMG first, extract the app from it (via hdiutil attach), copy the plugin manually to Contents/Library/QuickLook/, re‑sign the whole app bundle, then repack. But baking it into Install4j is cleaner.

Sign and Notarize the Plugin and App

macOS Gatekeeper demands everything signed and notarized. For Install4j:

  • On macOS build machine: Enable code signing in Install4j under General Settings > Code Signing. Specify your Developer ID cert. It scans JARs too—add any with binaries to “JAR files to be scanned.”
  • Plugin‑specific: Sign the .qlgenerator as mentioned, then let Install4j handle the app bundle.
  • Notarization: After DMG build, use xcrun notarytool submit YourApp.dmg --keychain-profile "your-notary-profile" --wait. Or Install4j can automate if building on macOS.
  • Windows builds? Sign JARs explicitly in Install4j, then notarize the DMG on macOS. Install4j notarization tips highlight scanning JARs for embedded executables.
  • Staple the ticket: xcrun stapler staple YourApp.app. Check with spctl --assess --type execute YourApp.app.

Install and Test the Bundled App

  1. Attach the DMG: hdiutil attach YourApp.dmg.
  2. Drag YourApp.app to /Applications.
  3. Open the app once (helps plugin discovery).
  4. Reset QuickLook: qlmanage -r (or qlmanage -r cache to clear thumbnails).
  5. List plugins: qlmanage -m—look for your.utitype -> /Applications/YourApp.app/Contents/Library/QuickLook/YourPlugin.qlgenerator.
  6. Test: Spacebar on a file or qlmanage -t /path/to/file.ext for thumbnail, -p for preview.

If it works, users see previews immediately after install. QuickLook debugging commands are gold for verification.

Common Troubleshooting Tips

Plugin not showing? Run qlmanage -m plugins—if missing, copy to /Library/QuickLook/ manually as a test (then qlmanage -r). Embedded ones sometimes lag until app launch.

Signing woes? codesign errors mean deep‑sign the bundle. Notarization fails? Check logs from notarytool; rescan JARs in Install4j.

Classic embedding issue: Works standalone but not bundled? Reset and relaunch app.

On Apple Silicon? Ensure universal binary. JavaScript app quirks? Treat the bundle like any Cocoa app—QuickLook doesn’t care about runtime.

Sources

  1. Beyond the good ol’ LaunchAgents - 12 - QuickLook Plugins — Install4j Copy Files steps for QuickLook bundling and qlmanage reset: https://theevilbit.github.io/beyond/beyond_0012/
  2. Creating a QuickLook plugin for a document-based macOS application — Embedding plugins in Contents/Library/QuickLook with build phases: https://fespinoza.github.io/creating-a-quicklook-plugin-for-a-document-based-macos-application
  3. A quick look at QuickLook and its problems — Plugin paths, qlmanage commands for listing and resetting: https://eclecticlight.co/2024/04/05/a-quick-look-at-quicklook-and-its-problems/
  4. Quicklook plugin doesn’t work when in app bundle — Troubleshooting embedded QuickLook plugins and registration: https://stackoverflow.com/questions/35875624/quicklook-plugin-doesnt-work-when-in-app-bundle
  5. Apple notarization fails with install4j generated DMG — Install4j code signing and notarization for macOS DMGs: https://stackoverflow.com/questions/64964010/apple-notarization-fails-with-install4j-generated-dmg

Conclusion

Bundling a QuickLook plugin into your Install4j macOS app boils down to smart Copy Files actions, rigorous signing, notarization, and a QuickLook reset—users love the seamless previews. Skip manual post‑DMG fiddling by configuring during build; test thoroughly with qlmanage. Nail this, and your JavaScript app stands out with pro‑level Finder integration. Questions on tweaks? Dive into those sources.

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Install QuickLook Plugin in Install4j macOS App Bundle