Fix manual offline model detection for Qwen package

Author: Android-PowerUser

app/src/main/kotlin/com/google/ai/sample/GenerativeAiViewModelFactory.kt

@@ -30,6 +30,7 @@ enum class ModelOption(
     val supportsScreenshot: Boolean = true,
     val isOfflineModel: Boolean = false,
     val offlineModelFilename: String? = null,
+    val offlineAlternateModelFilenames: List<String> = emptyList(),
     val offlineRequiredFilenames: List<String> = emptyList(),
     val additionalDownloadUrls: List<String> = emptyList(),
     val requiresVisionBackend: Boolean = false
@@ -77,6 +78,7 @@ enum class ModelOption(
         "6.3 GB",
         isOfflineModel = true,
         offlineModelFilename = "model_multimodal.litertlm",
+        offlineAlternateModelFilenames = listOf("model_quantized.litertlm"),
         offlineRequiredFilenames = listOf(
             "model_multimodal.litertlm",
             "sentencepiece.model",

app/src/main/kotlin/com/google/ai/sample/feature/multimodal/ModelDownloadManager.kt

@@ -66,12 +66,12 @@ object ModelDownloadManager {
     )
 
     fun isModelDownloaded(context: Context, model: ModelOption = GenerativeAiViewModelFactory.getCurrentModel()): Boolean {
-        val required = getRequiredFiles(context, model)
-        return required.isNotEmpty() && required.all { it.exists() && it.length() > 0 }
+        val modelFile = getModelFile(context, model)
+        return modelFile != null && modelFile.exists() && modelFile.length() > 0
     }
 
     fun getModelFile(context: Context, model: ModelOption = GenerativeAiViewModelFactory.getCurrentModel()): File? {
-        val modelFilename = model.offlineModelFilename ?: return null
+        val modelFilename = resolveInstalledModelFilename(context, model) ?: model.offlineModelFilename ?: return null
         val externalFilesDir = context.getExternalFilesDir(null)
         return if (externalFilesDir != null) {
             File(externalFilesDir, modelFilename)
@@ -83,26 +83,30 @@ object ModelDownloadManager {
 
     private fun getRequiredFiles(context: Context, model: ModelOption): List<File> {
         val externalFilesDir = context.getExternalFilesDir(null) ?: return emptyList()
-        val requiredNames = if (model.offlineRequiredFilenames.isNotEmpty()) {
+        val activeModelFilename = resolveInstalledModelFilename(context, model)
+        val requiredNames = if (model == ModelOption.QWEN3_5_4B_OFFLINE && activeModelFilename == "model_quantized.litertlm") {
+            listOf("model_quantized.litertlm", "sentencepiece.model")
+        } else if (model.offlineRequiredFilenames.isNotEmpty()) {
             model.offlineRequiredFilenames
         } else {
             listOfNotNull(model.offlineModelFilename)
         }
         return requiredNames.map { File(externalFilesDir, it) }
     }
 
-    fun getMissingRequiredFiles(context: Context, model: ModelOption): List<String> {
-        val externalFilesDir = context.getExternalFilesDir(null) ?: return model.offlineRequiredFilenames
-        val requiredNames = if (model.offlineRequiredFilenames.isNotEmpty()) {
-            model.offlineRequiredFilenames
-        } else {
-            listOfNotNull(model.offlineModelFilename)
-        }
-        return requiredNames.filter { name ->
+    private fun resolveInstalledModelFilename(context: Context, model: ModelOption): String? {
+        val externalFilesDir = context.getExternalFilesDir(null) ?: return null
+        val candidates = listOfNotNull(model.offlineModelFilename) + model.offlineAlternateModelFilenames
+        return candidates.firstOrNull { name ->
             val f = File(externalFilesDir, name)
-            !f.exists() || f.length() <= 0
+            f.exists() && f.length() > 0
         }
     }
+
+    fun getMissingRequiredFiles(context: Context, model: ModelOption): List<String> {
+        val requiredFiles = getRequiredFiles(context, model)
+        return requiredFiles.filter { !it.exists() || it.length() <= 0 }.map { it.name }
+    }
 
     private fun createNotificationChannel(context: Context) {
         if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {

app/src/main/kotlin/com/google/ai/sample/feature/multimodal/PhotoReasoningViewModel.kt

@@ -350,7 +350,9 @@ class PhotoReasoningViewModel(
                     )
                     if (liteRtEngine == null) {
                         val preferredBackend = if (backend == InferenceBackend.GPU) Backend.GPU() else Backend.CPU()
-                        val preferredVisionBackend = if (currentModel.requiresVisionBackend) {
+                        val useVisionBackend = currentModel.requiresVisionBackend &&
+                            modelFile.name.contains("multimodal", ignoreCase = true)
+                        val preferredVisionBackend = if (useVisionBackend) {
                             if (backend == InferenceBackend.GPU) Backend.GPU() else Backend.CPU()
                         } else {
                             null
@@ -413,7 +415,7 @@ class PhotoReasoningViewModel(
             if (msg.contains("litert_compiled_model", ignoreCase = true) ||
                 msg.contains("litert_tensor_buffer", ignoreCase = true)
             ) {
-                return "Offline model could not be initialized: LiteRT cannot compile this model package on this device. Ensure the full multimodal package files are present and try CPU backend."
+                return "Offline model could not be initialized: LiteRT cannot compile this model package on this device. Check model files and try CPU backend."
             }
             return if (msg.contains("memory", ignoreCase = true) || msg.contains("RAM", ignoreCase = true) || msg.contains("OOM", ignoreCase = true) || msg.contains("alloc", ignoreCase = true) || msg.contains("out of", ignoreCase = true)) {
                 "Not enough RAM to load the model on GPU. Try switching to CPU."