Add BackHandlerView hosting a Compose BackHandler

Author: colemancda

Demo/app/src/main/java/com/pureswift/swiftandroid/BackHandlerView.kt

@@ -0,0 +1,32 @@
+package com.pureswift.swiftandroid
+
+import android.content.Context
+import android.widget.FrameLayout
+import androidx.activity.compose.BackHandler
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.setValue
+import androidx.compose.ui.platform.ComposeView
+
+// Hosts a Jetpack Compose `BackHandler` to intercept the system back button and forward it to
+// Swift via `onBack()`. Renders no visible UI of its own; used only for its back-press interception.
+class BackHandlerView(context: Context, val callback: SwiftObject) : FrameLayout(context) {
+
+    private var handlerEnabled by mutableStateOf(true)
+
+    init {
+        val composeView = ComposeView(context)
+        composeView.setContent {
+            BackHandler(enabled = handlerEnabled) {
+                onBack()
+            }
+        }
+        addView(composeView)
+    }
+
+    fun setBackHandlerEnabled(value: Boolean) {
+        handlerEnabled = value
+    }
+
+    external fun onBack()
+}