Ios Keyboard Limitations

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name: ios-keyboard-limitations description: iOS keyboard extension technical limitations and workarounds. Use when planning or building iOS custom keyboards with voice/audio features, dictation, or system integration needs. Covers memory limits, sandbox restrictions, microphone access, app launching, and viable alternative architectures.

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iOS Keyboard Extension Limitations

When building iOS custom keyboards with voice/audio features, these are the hard limitations discovered through the PolyVoice project.

🔴 Hard Limitations (Cannot be worked around)

1. Microphone Access — DISALLOWED

Keyboard extensions cannot access the microphone.

AVAudioRecorder will fail with permission error

SFSpeechRecognizer is unavailable

No Siri integration from keyboard context

Why: Apple security model — keyboards run in sandbox and could keylog audio.

2. Open Other Apps — BLOCKED

Keyboards cannot programmatically open the main app or any other app.

UIApplication.shared.open() returns false

URL schemes don't work (myapp://)

ExtensionContext.open() not available

Why: Prevents malicious keyboards from launching apps without user consent.

3. Memory Limit — ~50MB

Keyboard extensions have strict memory limits (~30-60MB).

App terminated silently if exceeded

No crash log, just disappears

Heavy audio processing = instant death

Mitigation:

Record at 16kHz mono (not 44.1kHz)

Use 32kbps bitrate max

Immediate file cleanup after processing

60-second max recording hard limit

4. No Persistent Storage

UserDefaults unavailable, only App Groups.

Standard UserDefaults doesn't persist

Must use UserDefaults(suiteName: "group.com.company.app")

Requires App Group capability in both targets

5. Network Requires "Full Access"

API calls fail without user enabling "Allow Full Access" in Settings.

User must explicitly enable: Settings → General → Keyboard → [Keyboard Name] → Allow Full Access

Most users won't do this

Cannot prompt or explain from keyboard UI effectively

🟡 Partial Workarounds (User friction)

The "Open App" Workaround

Goal: Let user tap a button to open main app for recording.

Attempt:

// This does NOT work
extensionContext?.open(URL(string: "myapp://record")!)

Reality: Must use UIApplication.shared.open() outside extension context, but keyboards can't call this.

The Manual Switch Pattern

What actually works (with friction):

1. User taps button in keyboard → Shows alert: "Open PolyVoice to record?" 2. User manually switches to main app (Home button, swipe, etc.) 3. Main app detects active session (via App Groups / shared state) 4. Main app auto-records on appear 5. Auto-stops on silence (2 seconds) 6. Auto-copies to clipboard 7. User manually switches back to target app 8. Keyboard auto-pastes on reappear

User flow:

Keyboard → Tap mic → [Manual: Switch to app] → App auto-records → 
[Manual: Switch back] → Keyboard auto-pastes

Friction points:

Two manual app switches

Context switching breaks flow

Users forget to return

Clipboard may be overwritten

🟢 Alternative Architectures

Option 1: Share Extension (Better for Audio)

Use Share Sheet instead of keyboard.

Full app capabilities

Can record audio

Can process and return text

Limitation: Not a keyboard — user must open share sheet per text field.

Option 2: Full App Mode

Don't use keyboard extension — use main app only.

User opens app

Records dictation

Copies result

Switches to target app

Pastes manually

Benefit: No memory limits, full mic access, reliable. Cost: More friction than keyboard.

Option 3: Siri Shortcuts Integration

Provide Siri Shortcuts for voice-to-text.

"Hey Siri, dictate with PolyVoice"

Returns text to current app

Fully supported by Apple

Limitation: Not instant, requires Siri setup.

📊 Decision Matrix

| Approach | Mic Access | Memory | User Friction | Apple Approved | |----------|-----------|---------|---------------|----------------| | Keyboard extension | ❌ No | ⚠️ 50MB | Low (if no audio) | ✅ Yes | | Keyboard + audio workaround | ❌ No | ⚠️ 50MB | 🔴 High | ✅ Yes | | Share extension | ✅ Yes | ✅ Full | 🟡 Medium | ✅ Yes | | Full app only | ✅ Yes | ✅ Full | 🟡 Medium | ✅ Yes | | Siri Shortcuts | ✅ Yes | ✅ Full | 🟡 Medium | ✅ Yes |

🎯 Recommendation

For voice dictation/AI transcription:

1. Don't build a keyboard extension — the limitations make it frustrating 2. Use Share Extension — Apple-supported, full capabilities 3. Or full app — simplest to build, most reliable 4. Add Shortcuts — for power users who want speed

For non-audio keyboards (emoji, translation, etc.):

Keyboard extension works great. Just avoid audio features.

📚 References

Apple's official docs: https://developer.apple.com/documentation/uikit/keyboards_and_input/creating_a_custom_keyboard

Custom Keyboard Programming Guide (WWDC sessions)

PolyVoice project learnings (~/Projects/polyvoice-keyboard/)