[WIP] DI: implement simple local vm factory provider

examples/llama.android/app/src/main/java/com/example/llama/revamp/util/ViewModelFactoryProvider.kt

@@ -0,0 +1,52 @@
+package com.example.llama.revamp.util
+
+import androidx.lifecycle.ViewModel
+import androidx.lifecycle.ViewModelProvider
+import com.example.llama.revamp.data.preferences.UserPreferences
+import com.example.llama.revamp.engine.InferenceEngine
+import com.example.llama.revamp.monitoring.PerformanceMonitor
+import com.example.llama.revamp.viewmodel.MainViewModel
+import com.example.llama.revamp.viewmodel.PerformanceViewModel
+
+/**
+ * Utility class to provide ViewModel factories.
+ *
+ * TODO-han.yin: Replace with Hilt
+ */
+object ViewModelFactoryProvider {
+
+    /**
+     * Creates a factory for PerformanceViewModel.
+     */
+    fun getPerformanceViewModelFactory(
+        performanceMonitor: PerformanceMonitor,
+        userPreferences: UserPreferences
+    ): ViewModelProvider.Factory {
+        return object : ViewModelProvider.Factory {
+            @Suppress("UNCHECKED_CAST")
+            override fun <T : ViewModel> create(modelClass: Class<T>): T {
+                if (modelClass.isAssignableFrom(PerformanceViewModel::class.java)) {
+                    return PerformanceViewModel(performanceMonitor, userPreferences) as T
+                }
+                throw IllegalArgumentException("Unknown ViewModel class: ${modelClass.name}")
+            }
+        }
+    }
+
+    /**
+     * Creates a factory for MainViewModel.
+     */
+    fun getMainViewModelFactory(
+        inferenceEngine: InferenceEngine
+    ): ViewModelProvider.Factory {
+        return object : ViewModelProvider.Factory {
+            @Suppress("UNCHECKED_CAST")
+            override fun <T : ViewModel> create(modelClass: Class<T>): T {
+                if (modelClass.isAssignableFrom(MainViewModel::class.java)) {
+                    return MainViewModel(inferenceEngine) as T
+                }
+                throw IllegalArgumentException("Unknown ViewModel class: ${modelClass.name}")
+            }
+        }
+    }
+}