diff --git a/lib/flutter_tindercard.dart b/lib/flutter_tindercard.dart
index 0d9787c..f9be512 100644
--- a/lib/flutter_tindercard.dart
+++ b/lib/flutter_tindercard.dart
@@ -48,6 +48,7 @@ class TinderSwapCard extends StatefulWidget {
   /// value of alignment, 0.0 means middle, so it need bigger than zero.
   /// and size control params;
   TinderSwapCard({
+    Key key,
     @required CardBuilder cardBuilder,
     @required int totalNum,
     AmassOrientation orientation = AmassOrientation.bottom,
@@ -77,7 +78,8 @@ class TinderSwapCard extends StatefulWidget {
         _swipeEdgeVertical = swipeEdgeVertical,
         _swipeUp = swipeUp,
         _swipeDown = swipeDown,
-        _allowVerticalMovement = allowVerticalMovement {
+        _allowVerticalMovement = allowVerticalMovement,
+        super(key: key) {
     final widthGap = maxWidth - minWidth;
     final heightGap = maxHeight - minHeight;