Understanding Capacitor Architecture

Capacitor Runtime Model

Capacitor embeds a WebView inside a native app shell. Communication between JavaScript and native layers happens via plugin APIs and a bridge layer. Misuse of this bridge often causes silent failures or inconsistent behaviors.

Plugin-Based Extensibility

Plugins are at the heart of Capacitor's extensibility. Poor plugin implementations, mismatched versions, or missing platform code can result in compilation errors or broken features at runtime.

Common Issues and Root Causes

1. Plugin Not Registered Error

Occurs when a custom or third-party plugin fails to load due to missing native registration code. Often seen after migrating to Capacitor v5 or manually editing native files.

// Android - MainActivity.java
import com.getcapacitor.Plugin; // Ensure custom plugin is imported
add(new MyCustomPlugin());

2. iOS White Screen on Launch

Typically caused by improper splash screen handling, missing assets, or JavaScript errors before the WebView loads. It can also be linked to Cordova plugin remnants that conflict with Capacitor's lifecycle.

3. Inconsistent File Handling

Capacitor File System APIs behave differently across platforms. For example, writing to `Directory.Documents` on iOS stores files in app-scoped sandbox, while on Android it could map to external storage depending on API level.

Step-by-Step Diagnostics

1. Inspect the Console Log

Use adb logcat for Android and Xcode's console for iOS. Pay close attention to plugin registration errors, file path issues, or native bridge messages.

2. Verify Plugin Sync Status

After installing plugins, always run:

npx cap sync
npx cap update ios
npx cap update android

Missing this step leaves native code in an inconsistent state with JavaScript references.

3. Validate WebView Load

Enable remote debugging (Chrome DevTools for Android, Safari Inspector for iOS) to check JavaScript errors or blank page loads.

Fixing Common Problems

Plugin Not Detected

• Ensure correct native imports (Android/iOS)
• Check capacitor.config.ts for plugin inclusion
• Clean native build folders (npx cap clean)

Splash Screen and White Screen Fix

• Update @capacitor/splash-screen and configure launchShowDuration
• Wrap app.mount() in DOMContentLoaded to delay rendering until platform ready

File System Path Resolution

// Example: Write a file to Capacitor Filesystem
Filesystem.writeFile({
  path: "data.json",
  data: JSON.stringify(data),
  directory: Directory.Documents,
});

Always use FilesystemDirectory enums and avoid hardcoded paths.

Platform-Specific Debugging

Android

• Use adb logcat | grep Capacitor to isolate logs
• Validate AndroidManifest.xml for required permissions (camera, file)

iOS

• Use Xcode Organizer for crash logs
• Ensure Info.plist has necessary entries for plugins (e.g., camera usage)
• Confirm WebView loads by adding console logs early in JS entry point

Best Practices for Enterprise Apps

• Pin Capacitor versions across team with package-lock.json
• Isolate custom plugins into separate libraries
• Always test on physical devices, not just emulators
• Document native changes after each sync/update

Conclusion

Capacitor offers powerful hybrid capabilities, but requires disciplined debugging and version control to work reliably across platforms. Most issues stem from missing syncs, unregistered plugins, or mismatched native expectations. By following structured diagnostics and understanding Capacitor's internals, teams can confidently build and maintain high-performance mobile apps in production environments.

FAQs

1. Why is my plugin working on Android but not iOS?

Likely due to missing Objective-C/Swift registration in the iOS plugin source. Ensure plugin is listed in AppDelegate.swift.

2. How do I handle deep links in Capacitor?

Use the App.addListener('appUrlOpen') event and configure Associated Domains in iOS and intent filters in AndroidManifest.xml.

3. What causes "Cannot read properties of undefined" with Capacitor APIs?

It usually means the plugin failed to load. Confirm sync was run and that you're referencing the plugin from the correct scope.

4. Why does the iOS app crash after plugin installation?

Possibly due to native code mismatch or missing permissions. Always rebuild in Xcode and validate required capabilities.

5. Can I use Cordova plugins with Capacitor?

Yes, but compatibility is not guaranteed. Prefer native Capacitor plugins or build custom plugins following Capacitor's plugin development guide.