Fix update Sheet content while initializing (#432)

@@ -373,11 +373,18 @@ class __SheetRouteContainerState extends State<_SheetRouteContainer>
     _routeController.addListener(onRouteAnimationUpdate);
     _sheetController.addListener(onSheetExtentUpdate);
     WidgetsBinding.instance.addPostFrameCallback((Duration timeStamp) {
-      _sheetController.relativeAnimateTo(
+      _sheetController
+          .relativeAnimateTo(
         route.initialExtent,
         duration: route.transitionDuration,
         curve: route.animationCurve ?? Curves.easeOut,
-      );
+      )
+          .then((_) {
+        if (_sheetController.hasClients) {
+          (_sheetController.position.context as SheetContext)
+              .initialAnimationFinished = true;
+        }
+      });
     });
     super.initState();
   }

@@ -122,7 +122,12 @@ class SheetPrimaryScrollPosition extends ScrollPositionWithSingleContext {
     }
 
     if (sheetPosition.hasContentDimensions) {
-      sheetPosition.goBallistic(velocity);
+      if (sheetContext.initialAnimationFinished) {
+        sheetPosition.goBallistic(velocity);
+      } else {
+        goIdle();
+        return;
+      }
     }
 
     if (velocity > 0.0 &&

@@ -25,6 +25,8 @@ import 'package:sheet/src/widgets/min_interaction.dart';
 abstract class SheetContext extends ScrollContext {
   double? get initialExtent;
   SheetPosition get position;
+  bool get initialAnimationFinished;
+  set initialAnimationFinished(bool initialAnimationFinished);
 }
 
 /// A widget that transform to user drag.
@@ -326,6 +328,9 @@ class SheetState extends State<SheetScrollable>
   @override
   AxisDirection get axisDirection => widget.axisDirection;
 
+  @override
+  bool initialAnimationFinished = false;
+
   late SheetBehavior _configuration;
   ScrollPhysics? _physics;
   SheetController? _fallbackScrollController;
@@ -775,7 +780,7 @@ class _ScrollSemantics extends SingleChildRenderObjectWidget {
     required this.allowImplicitScrolling,
     required this.semanticChildCount,
     super.child,
-  })  : assert(semanticChildCount == null || semanticChildCount >= 0);
+  }) : assert(semanticChildCount == null || semanticChildCount >= 0);
 
   final ScrollPosition position;
   final bool allowImplicitScrolling;