CodeKeyboard Part 1: Why, and the Three Layers

Why this exists

CodeKeyboard is a system Android keyboard (IME), not a text box demo. The layout is Sofle-inspired: split halves, column stagger, multiple layers, home-row modifiers. The point is coder-friendly modifiers and layers on a phone, plus prediction that can learn personal and mixed-script typing (for example Banglish) without a server.

React Native is still in the repo for the launcher app: settings, themes, snippet management, layout preview. The keys you type with in other apps are not RN views. They are a Kotlin View subclass drawn on a Canvas inside InputMethodService.

docs/architecture/overview.md still draws RN as transitional and lists an older component set. Treat that diagram as direction, then read the Kotlin package for what runs today.

Three layers

Launcher app (React Native)
  settings, themes, preview keyboard
        |
        |  optional bridge (layout JSON, snippets, settings)
        v
IME process (Kotlin)
  CodeKeyboardIME
  NativeKeyboardView, KeyboardState, ComposingBuffer
  Trie, UserTrie, BigramModel, SuggestionBarView, EmojiPanelView
        |
        |  InputConnection only
        v
Host app field

You never find the host EditText in the view tree. You only use InputConnection methods: commitText, setComposingText, finishComposingText, deleteSurroundingText, sendKeyEvent, performEditorAction, getTextBeforeCursor, and so on.

Register the IME

android/app/src/main/AndroidManifest.xml:

<service
    android:name=".CodeKeyboardIME"
    android:label="@string/ime_name"
    android:permission="android.permission.BIND_INPUT_METHOD"
    android:exported="true">
  <intent-filter>
    <action android:name="android.view.InputMethod" />
  </intent-filter>
  <meta-data
      android:name="android.view.im"
      android:resource="@xml/method" />
</service>

res/xml/method.xml points settings at .MainActivity. After install the user must enable the IME in system settings. That is normal Android.

What ships vs what ADRs name

supportsComposing

Set in CodeKeyboardIME.onStartInput:

supportsComposing = when {
    editorInfo == null -> false
    editorInfo.inputType == InputType.TYPE_NULL -> false
    isPasswordField(editorInfo) -> false
    isNumericField(editorInfo) -> false
    else -> true
}

• TYPE_NULL: terminals / raw key hosts (for example Termux).
• Password variations: no underlined composing.
• Number, phone, datetime classes: direct commits.

When false, characters go through commitText (or key events) without building a composing region the same way.

onCreate wiring (preview of later parts)

trie = Trie.load(this)
userTrie = UserTrie.load(File(filesDir, "user.trie"))
bigramModel = BigramModel(this).also { it.load() }
suggestionStrategy = BigramAwareSuggestionStrategy(
    MergedSuggestionStrategy(userTrie, trie), bigramModel)
wordLearner = WordLearner(userTrie) { word ->
    trie.suggest(word, 1).firstOrNull() == word
}

That single stack is the whole suggestion product: user trie, base trie, fuzzy fill inside Merged, bigram promotion outside.

Verification (part 1)