1. simplified suggestion scrolling; 2. hopefully fixed the 'spans can not have zero length' warning; 3. fixed repeated words popping over and over again, when scrolling the suggestions in Amazon Kindle app, on the Share Document screen (AppHacks established)

src/io/github/sspanak/tt9/ime/KeyPadHandler.java

@@ -74,8 +74,8 @@ abstract class KeyPadHandler extends InputMethodService {
 	 */
 	@Override
 	public void onStartInput(EditorInfo inputField, boolean restarting) {
+		// Logger.d("T9.onStartInput", "inputType: " + inputField.inputType + " fieldId: " + inputField.fieldId + " fieldName: " + inputField.fieldName + " packageName: " + inputField.packageName + " privateImeOptions: " + inputField.privateImeOptions + " imeOptions: " + inputField.imeOptions + " extras: " + inputField.extras);
 		currentInputConnection = getCurrentInputConnection();
-		// Logger.d("T9.onStartInput", "inputType: " + inputField.inputType + " fieldId: " + inputField.fieldId + " fieldName: " + inputField.fieldName + " packageName: " + inputField.packageName);
 		onStart(inputField);
 	}
 

src/io/github/sspanak/tt9/ime/TraditionalT9.java

@@ -18,6 +18,7 @@ import java.util.List;
 import io.github.sspanak.tt9.Logger;
 import io.github.sspanak.tt9.R;
 import io.github.sspanak.tt9.db.DictionaryDb;
+import io.github.sspanak.tt9.ime.helpers.AppHacks;
 import io.github.sspanak.tt9.ime.helpers.InputModeValidator;
 import io.github.sspanak.tt9.ime.helpers.InputType;
 import io.github.sspanak.tt9.ime.helpers.TextField;
@@ -35,6 +36,7 @@ import io.github.sspanak.tt9.ui.tray.SuggestionsBar;
 public class TraditionalT9 extends KeyPadHandler {
 	// internal settings/data
 	private boolean isActive = false;
+	@NonNull private AppHacks appHacks = new AppHacks(null, null);
 	@NonNull private TextField textField = new TextField(null, null);
 	@NonNull private InputType inputType = new InputType(null, null);
 	@NonNull private final Handler autoAcceptHandler = new Handler(Looper.getMainLooper());
@@ -202,6 +204,7 @@ public class TraditionalT9 extends KeyPadHandler {
 	protected void onStart(EditorInfo input) {
 		inputType = new InputType(currentInputConnection, input);
 		textField = new TextField(currentInputConnection, input);
+		appHacks = new AppHacks(input, textField);
 
 		if (!inputType.isValid() || inputType.isLimited()) {
 			// When the input is invalid or simple, let Android handle it.
@@ -242,6 +245,10 @@ public class TraditionalT9 extends KeyPadHandler {
 
 
 	public boolean onBackspace() {
+		if (appHacks.onBackspace(mInputMode)) {
+			return true;
+		}
+
 		// 1. Dialer fields seem to handle backspace on their own and we must ignore it,
 		// otherwise, keyDown race condition occur for all keys.
 		// 2. Allow the assigned key to function normally, when there is no text (e.g. "Back" navigates back)
@@ -296,7 +303,7 @@ public class TraditionalT9 extends KeyPadHandler {
 		}
 
 		if (mInputMode.shouldSelectNextSuggestion() && !isSuggestionViewHidden()) {
-			nextSuggestion();
+			onKeyScrollSuggestion(false, false);
 			scheduleAutoAccept(mInputMode.getAutoAcceptTimeout());
 		} else {
 			getSuggestions();
@@ -311,9 +318,9 @@ public class TraditionalT9 extends KeyPadHandler {
 
 		if (isSuggestionViewHidden()) {
 			return performOKAction();
-		} else {
-			acceptCurrentSuggestion(KeyEvent.KEYCODE_ENTER);
 		}
+
+		acceptCurrentSuggestion(KeyEvent.KEYCODE_ENTER);
 		return true;
 	}
 
@@ -425,10 +432,9 @@ public class TraditionalT9 extends KeyPadHandler {
 		}
 
 		cancelAutoAccept();
-		if (backward) previousSuggestion();
+		suggestionBar.scrollToSuggestion(backward ? -1 : 1);
-		else nextSuggestion();
 		mInputMode.setWordStem(suggestionBar.getCurrentSuggestion(), true);
-		textField.setComposingTextWithHighlightedStem(suggestionBar.getCurrentSuggestion(), mInputMode);
+		setComposingTextWithHighlightedStem(suggestionBar.getCurrentSuggestion());
 		return true;
 	}
 
@@ -493,12 +499,18 @@ public class TraditionalT9 extends KeyPadHandler {
 
 	@Override
 	public void onUpdateSelection(int oldSelStart, int oldSelEnd, int newSelStart, int newSelEnd, int candidatesStart, int candidatesEnd) {
+		// Logger.d("onUpdateSelection", "oldSelStart: " + oldSelStart + " oldSelEnd: " + oldSelEnd + " newSelStart: " + newSelStart + " oldSelEnd: " + oldSelEnd + " candidatesStart: " + candidatesStart + " candidatesEnd: " + candidatesEnd);
+
 		super.onUpdateSelection(oldSelStart, oldSelEnd, newSelStart, newSelEnd, candidatesStart, candidatesEnd);
 
 		// If the cursor moves while composing a word (usually, because the user has touched the screen outside the word), we must
 		// end typing end accept the word. Otherwise, the cursor would jump back at the end of the word, after the next key press.
 		// This is confusing from user perspective, so we want to avoid it.
-		if (!suggestionBar.isEmpty() && (newSelStart != candidatesEnd || newSelEnd != candidatesEnd)) {
+		if (
+			candidatesStart != -1 && candidatesEnd != -1
+			&& (newSelStart != candidatesEnd || newSelEnd != candidatesEnd)
+			&& !suggestionBar.isEmpty()
+		) {
 			acceptIncompleteSuggestion();
 		}
 	}
@@ -509,18 +521,6 @@ public class TraditionalT9 extends KeyPadHandler {
 	}
 
 
-	private void previousSuggestion() {
-		suggestionBar.scrollToSuggestion(-1);
-		textField.setComposingTextWithHighlightedStem(suggestionBar.getCurrentSuggestion(), mInputMode);
-	}
-
-
-	private void nextSuggestion() {
-		suggestionBar.scrollToSuggestion(1);
-		textField.setComposingTextWithHighlightedStem(suggestionBar.getCurrentSuggestion(), mInputMode);
-	}
-
-
 	private boolean scheduleAutoAccept(int delay) {
 		cancelAutoAccept();
 
@@ -624,7 +624,7 @@ public class TraditionalT9 extends KeyPadHandler {
 		// for a more intuitive experience.
 		String word = suggestionBar.getCurrentSuggestion();
 		word = word.substring(0, Math.min(mInputMode.getSequenceLength(), word.length()));
-		textField.setComposingTextWithHighlightedStem(word, mInputMode);
+		setComposingTextWithHighlightedStem(word);
 	}
 
 
@@ -665,6 +665,15 @@ public class TraditionalT9 extends KeyPadHandler {
 	}
 
 
+	private void setComposingTextWithHighlightedStem(@NonNull String word) {
+		if (appHacks.setComposingTextWithHighlightedStem(word)) {
+			Logger.w("highlightComposingText", "Defective text field detected! Text highlighting disabled.");
+		} else {
+			textField.setComposingTextWithHighlightedStem(word, mInputMode);
+		}
+	}
+
+
 	private void nextInputMode() {
 		if (mInputMode.isPassthrough()) {
 			return;

src/io/github/sspanak/tt9/ime/helpers/AppHacks.java

@@ -0,0 +1,42 @@
+package io.github.sspanak.tt9.ime.helpers;
+
+import android.view.inputmethod.EditorInfo;
+
+import androidx.annotation.NonNull;
+
+import io.github.sspanak.tt9.ime.modes.InputMode;
+
+public class AppHacks {
+	private final EditorInfo editorInfo;
+	private final TextField textField;
+
+
+	public AppHacks(EditorInfo inputField, TextField textField) {
+		this.editorInfo = inputField;
+		this.textField = textField;
+	}
+
+
+	private boolean isKindleInvertedTextField() {
+		return editorInfo != null && editorInfo.inputType == 1 && editorInfo.packageName.contains("com.amazon.kindle");
+	}
+
+
+	public boolean setComposingTextWithHighlightedStem(@NonNull String word) {
+		if (isKindleInvertedTextField()) {
+			textField.setComposingText(word);
+			return true;
+		}
+
+		return false;
+	}
+
+
+	public boolean onBackspace(InputMode inputMode) {
+		if (isKindleInvertedTextField()) {
+			inputMode.clearWordStem();
+		}
+
+		return false;
+	}
+}

src/io/github/sspanak/tt9/ime/helpers/TextField.java

@@ -274,13 +274,13 @@ public class TextField {
 	 * the text will be in bold and italic.
 	 */
 	private CharSequence highlightText(CharSequence word, int start, int end, boolean highlightMore) {
-		if (end < start || start < 0) {
+		if (end <= start || start < 0) {
 			Logger.w("tt9.util.highlightComposingText", "Cannot highlight invalid composing text range: [" + start + ", " + end + "]");
 			return word;
 		}
 
-		// nothing to highlight in an empty word
+		// nothing to highlight in an empty word or if the target is beyond the last letter
-		if (word == null || word.length() == 0) {
+		if (word == null || word.length() == 0 || word.length() <= start) {
 			return word;
 		}
 

src/io/github/sspanak/tt9/ui/tray/SuggestionsBar.java

@@ -7,6 +7,7 @@ import android.graphics.drawable.Drawable;
 import android.os.Handler;
 import android.view.View;
 
+import androidx.annotation.NonNull;
 import androidx.core.content.ContextCompat;
 import androidx.recyclerview.widget.DefaultItemAnimator;
 import androidx.recyclerview.widget.DividerItemDecoration;
@@ -106,6 +107,7 @@ public class SuggestionsBar {
 	}
 
 
+	@NonNull
 	public String getSuggestion(int id) {
 		if (id < 0 || id >= suggestions.size()) {
 			return "";