Fix the ClassCastException in DemoActivity

The R.id.motionlayout could be other Views (such as DrawerLayout in
motion_13_drawerlayout.xml)

Author: thagikura

motionlayout/src/main/java/com/google/androidstudio/motionlayoutexample/DemoActivity.kt

@@ -26,24 +26,25 @@ import android.widget.ImageView
 
 @RequiresApi(Build.VERSION_CODES.LOLLIPOP) // for View#clipToOutline
 class DemoActivity : AppCompatActivity() {
-    private lateinit var motionLayout : MotionLayout
+    private lateinit var container: View
 
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
         val layout = intent.getIntExtra("layout_file_id", R.layout.motion_01_basic)
         setContentView(layout)
-        motionLayout = findViewById(R.id.motionLayout)
+        container = findViewById(R.id.motionLayout)
 
         if (layout == R.layout.motion_11_coordinatorlayout) {
             val icon = findViewById<ImageView>(R.id.icon)
             icon?.clipToOutline = true
         }
 
         val doShowPaths = intent.getBooleanExtra("showPaths", false)
-        motionLayout.setShowPaths(doShowPaths)
+        (container as? MotionLayout)?.setShowPaths(doShowPaths)
     }
 
     fun changeState(v: View?) {
+        val motionLayout = container as? MotionLayout ?: return
         if (motionLayout.progress > 0.5f) {
             motionLayout.transitionToStart()
         } else {