Migrate catalog app to Kotlin Multiplatform

[ellykits]

IMPORTANT: All PRs must be linked to an issue (except for extremely trivial and straightforward changes).

Fixes #2941

Description
Clear and concise code change description.

Alternative(s) considered
Have you considered any alternatives? And if so, why have you chosen the approach in this PR?

Type
Choose one: (Bug fix | Feature | Documentation | Testing | Code health | Builds | Releases | Other)

Screenshots (if applicable)

Checklist

• I have read and acknowledged the Code of conduct.
• I have read the Contributing page.
• I have signed the Google Individual CLA, or I am covered by my company's Corporate CLA.
• I have discussed my proposed solution with code owners in the linked issue(s) and we have agreed upon the general approach.
• I have run ./gradlew spotlessApply and ./gradlew spotlessCheck to check my code follows the style guide of this project.
• I have run ./gradlew check and ./gradlew connectedCheck to test my changes locally.
• I have built and run the demo app(s) to verify my change fixes the issue and/or does not break the demo app(s).

[ellykits]

Marked this as ready for review and created an issue to track remaining features that aren't blocking testing questionnaires via catalog application here #2942

[ellykits]

DataCapture Issues Report

Generated on: 2026-02-23

---

1. General

• [x] Cross-platform open questionnaire not implemented (TBD via Implement an open questionnaire menu action for different platforms for the catalog app. #2943)
• QuestionnaireResponse Only captures the answer value; additional
  information for the questionnaire item that is missing.

---

2. Components

Slider

• Creates items above the maximum that is allowed

Label

• Appear small compared to the previous label widget

Not working

• Repeated Group
• Date and Time fields
• Attachment
• Locations (Misc)
• Initial value (Misc)
• Custom styling (Misc)

Help Icon

• Do not use filled icon, use outline
• Has no toggle error state icon

Item Answer Media

• Not working for both datacapture and datacapture kmp modules

---

3. Layout

• Of course, date fields are not working, affecting skip logic
• Labels are rather darkened or bold
• Validation dialog not displayed on Default
• Cannot submit multiple times too
• No validation happening for paginated UI too
• Review not pre-populated (On display and on edit)
• Read-only not working

---

4. Behaviors

Calculated expression

• Calculated expression not working (possibly because of a missing
  date time field). Info displayed on top instead of below.

Answer expression

• Answer expression crashes the app, see log below

Log Snippet

    java.lang.IllegalStateException: XFhirQueryResolver cannot be null. Please provide the XFhirQueryResolver via DataCaptureConfig.
        at com.google.android.fhir.datacapture.expressions.EnabledAnswerOptionsEvaluator.resolveAnswerExpression(EnabledAnswerOptionsEvaluator.kt:200)
        at com.google.android.fhir.datacapture.expressions.EnabledAnswerOptionsEvaluator.answerOptions(EnabledAnswerOptionsEvaluator.kt:133)
        at com.google.android.fhir.datacapture.expressions.EnabledAnswerOptionsEvaluator.evaluate$datacapture_kmp(EnabledAnswerOptionsEvaluator.kt:92)
        at com.google.android.fhir.datacapture.QuestionnaireViewModel.getQuestionnaireAdapterItems(QuestionnaireViewModel.kt:1022)
        at com.google.android.fhir.datacapture.QuestionnaireViewModel.getQuestionnaireAdapterItems(QuestionnaireViewModel.kt:971)
        at com.google.android.fhir.datacapture.QuestionnaireViewModel.getQuestionnaireAdapterItems$default(QuestionnaireViewModel.kt:964)
        at com.google.android.fhir.datacapture.QuestionnaireViewModel.getQuestionnaireState(QuestionnaireViewModel.kt:832)
        at com.google.android.fhir.datacapture.QuestionnaireViewModel.access$getQuestionnaireState(QuestionnaireViewModel.kt:104)
        at com.google.android.fhir.datacapture.QuestionnaireViewModel$questionnaireStateFlow$1.invokeSuspend(QuestionnaireViewModel.kt:654)
        at com.google.android.fhir.datacapture.QuestionnaireViewModel$questionnaireStateFlow$1.invoke(Unknown Source:9)
        at com.google.android.fhir.datacapture.QuestionnaireViewModel$questionnaireStateFlow$1.invoke(Unknown Source:20)

Skip logic

• Skip logic not working because of a missing date field
• The info displayed at the top of the progress bar should be
  below, right above the bottom navigation page
• Skip logic with expression crashes with the log below

Log Snippet

    Process: com.google.android.fhir.catalog, PID: 5853
    java.lang.IllegalStateException: Unknown variable: %has
        at com.google.fhir.fhirpath.FhirPathEvaluator.visitExternalConstantTerm(FhirPathEvaluator.kt:360)
        at com.google.fhir.fhirpath.FhirPathEvaluator.visitExternalConstantTerm(FhirPathEvaluator.kt:62)
        at com.google.fhir.fhirpath.parsers.fhirpathParser$ExternalConstantTermContext.accept(fhirpathParser.kt:985)
        at org.antlr.v4.kotlinruntime.tree.AbstractParseTreeVisitor.visitChildren(AbstractParseTreeVisitor.kt:41)
        at com.google.fhir.fhirpath.parsers.fhirpathBaseVisitor.visitTermExpression(fhirpathBaseVisitor.kt:91)
        at com.google.fhir.fhirpath.parsers.fhirpathParser$TermExpressionContext.accept(fhirpathParser.kt:573)
        at org.antlr.v4.kotlinruntime.tree.AbstractParseTreeVisitor.visit(AbstractParseTreeVisitor.kt:11)
        at com.google.fhir.fhirpath.FhirPathEvaluator.visitAdditiveExpression(FhirPathEvaluator.kt:164)
        at com.google.fhir.fhirpath.FhirPathEvaluator.visitAdditiveExpression(FhirPathEvaluator.kt:62)
        at com.google.fhir.fhirpath.parsers.fhirpathParser$AdditiveExpressionContext.accept(fhirpathParser.kt:284)
        at org.antlr.v4.kotlinruntime.tree.AbstractParseTreeVisitor.visit(AbstractParseTreeVisitor.kt:11)
        at com.google.fhir.fhirpath.FhirPathEngine.evaluateExpression(FhirPathEngine.kt:82)
        at com.google.android.fhir.datacapture.fhirpath.ExpressionEvaluator.evaluateExpression(ExpressionEvaluator.kt:150)
        at com.google.android.fhir.datacapture.enablement.EnablementEvaluator.evaluate(EnablementEvaluator.kt:150)
        at com.google.android.fhir.datacapture.QuestionnaireViewModel.getQuestionnaireAdapterItems(QuestionnaireViewModel.kt:988)
        at com.google.android.fhir.datacapture.QuestionnaireViewModel.getQuestionnaireAdapterItems(QuestionnaireViewModel.kt:971)
        at com.google.android.fhir.datacapture.QuestionnaireViewModel.getQuestionnaireAdapterItems$default(QuestionnaireViewModel.kt:964)

Dynamic question

• Dynamic question not working, possibly because of the missing
  date time field (should be updated when an option is selected on the
  choose option widget)

Questionnaire constraint

• Questionnaire constraint not working, failing with the error logs
  below

Log Snippet

    FATAL EXCEPTION: main (Fix with AI)
    Process: com.google.android.fhir.catalog, PID: 5918
    java.lang.IllegalStateException: Unknown variable: %context
        at com.google.fhir.fhirpath.FhirPathEvaluator.visitExternalConstantTerm(FhirPathEvaluator.kt:360)
        at com.google.fhir.fhirpath.FhirPathEvaluator.visitExternalConstantTerm(FhirPathEvaluator.kt:62)
        at com.google.fhir.fhirpath.parsers.fhirpathParser$ExternalConstantTermContext.accept(fhirpathParser.kt:985)
        at org.antlr.v4.kotlinruntime.tree.AbstractParseTreeVisitor.visitChildren(AbstractParseTreeVisitor.kt:41)
        at com.google.fhir.fhirpath.parsers.fhirpathBaseVisitor.visitTermExpression(fhirpathBaseVisitor.kt:91)
        at com.google.fhir.fhirpath.parsers.fhirpathParser$TermExpressionContext.accept(fhirpathParser.kt:573)
        at org.antlr.v4.kotlinruntime.tree.AbstractParseTreeVisitor.visit(AbstractParseTreeVisitor.kt:11)
        at com.google.fhir.fhirpath.FhirPathEvaluator.visitInvocationExpression(FhirPathEvaluator.kt:110)
        at com.google.fhir.fhirpath.FhirPathEvaluator.visitInvocationExpression(FhirPathEvaluator.kt:62)
        at com.google.fhir.fhirpath.parsers.fhirpathParser$InvocationExpressionContext.accept(fhirpathParser.kt:487)
        at org.antlr.v4.kotlinruntime.tree.AbstractParseTreeVisitor.visit(AbstractParseTreeVisitor.kt:11)
        at com.google.fhir.fhirpath.FhirPathEvaluator.visitInvocationExpression(FhirPathEvaluator.kt:110)
        at com.google.fhir.fhirpath.FhirPathEvaluator.visitInvocationExpression(FhirPathEvaluator.kt:62)
        at com.google.fhir.fhirpath.parsers.fhirpathParser$InvocationExpressionContext.accept(fhirpathParser.kt:487)
        at org.antlr.v4.kotlinruntime.tree.AbstractParseTreeVisitor.visit(AbstractParseTreeVisitor.kt:11)
        at com.google.fhir.fhirpath.FhirPathEvaluator.visitEqualityExpression(FhirPathEvaluator.kt:218)
        at com.google.fhir.fhirpath.FhirPathEvaluator.visitEqualityExpression(FhirPathEvaluator.kt:62)
        at com.google.fhir.fhirpath.parsers.fhirpathParser$EqualityExpressionContext.accept(fhirpathParser.kt:516)
        at org.antlr.v4.kotlinruntime.tree.AbstractParseTreeVisitor.visit(AbstractParseTreeVisitor.kt:11)
        at com.google.fhir.fhirpath.FhirPathEngine.evaluateExpression(FhirPathEngine.kt:82)
        at com.google.android.fhir.datacapture.fhirpath.ExpressionEvaluator.evaluateExpression(ExpressionEvaluator.kt:150)
        at com.google.android.fhir.datacapture.fhirpath.ExpressionEvaluator.evaluateExpression$default(ExpressionEvaluator.kt:145)
        at com.google.android.fhir.datacapture.validation.ConstraintItemExtensionValidator.validate(ConstraintItemExtensionValidator.kt:77)
        at com.google.android.fhir.datacapture.validation.QuestionnaireResponseItemValidator.validate(QuestionnaireResponseItemValidator.kt:55)

[ellykits]

Catalog app demo in pics and video

Android Emulator demo

catalog_demo.mp4

iOS simulator

Android

Desktop