fix some errors

Samples/UIWidgetsSamples_2019_4/Assets/UIWidgetsGallery/demo/cupertino/cupertino_navigation_demo.cs

                                                             decoration: new BoxDecoration(
                                                                 image: new DecorationImage(
                                                                     image: new FileImage(
-                                                                        file: "logo.png"
+                                                                        file: "people/square/trevor.png"
                                                                     )
                                                                 ),
                                                                 shape: BoxShape.circle
                                                             decoration: new BoxDecoration(
                                                                 image: new DecorationImage(
                                                                     image: new FileImage(
-                                                                        "logo.png"
+                                                                        "people/square/sandra.png"
                                                                     )
                                                                 ),
                                                                 shape: BoxShape.circle

Samples/UIWidgetsSamples_2019_4/Assets/UIWidgetsGallery/demo/shrine/backdrop.cs

                               )
                             ),
                             new FractionalTranslation(
-                              translation: new Tween<Offset>(
+                              translation: new OffsetTween(
                               begin: Offset.zero,
                               end: new Offset(1.0f, 0.0f)).evaluate(animation),
                               child: new Container(
                                 curve: new Interval(0.5f, 1.0f)
                             ).value,
                             child: new FractionalTranslation(
-                                translation: new Tween<Offset>(
+                                translation: new OffsetTween(
                                 begin: Offset.zero,
                                 end: new Offset(0.5f, 0.0f)).evaluate(animation),
                                 child: backTitle
                                 parent: animation,
                                 curve: new Interval(0.5f, 1.0f)).value,
                             child: new FractionalTranslation(
-                            translation: new Tween<Offset>(
+                            translation: new OffsetTween(
                                 begin: new Offset(-0.25f, 0.0f),
                                 end: Offset.zero).evaluate(animation),
                             child: frontTitle

Samples/UIWidgetsSamples_2019_4/Assets/UIWidgetsGallery/demo/shrine/expanding_bottom_sheet.cs

         public static readonly float _kCornerRadius = 24.0f;
         public static readonly float _kWidthForCartIcon = 64.0f;
         
-        public static Animation<T> _getEmphasizedEasingAnimation<T>(
-            T begin,
-            T peak,
-            T end,
+        public static Animation<float> _getFloatEmphasizedEasingAnimation(
+            float begin,
+            float peak,
+            float end,
             bool isForward,
             Animation<float> parent
         ) {
                 secondWeight = _kPeakVelocityTime;
             }
 
-            return new TweenSequence<T>(
-                new List<TweenSequenceItem<T>>{
-                    new TweenSequenceItem<T>(
+            return new TweenSequence<float>(
+                new List<TweenSequenceItem<float>>{
+                    new TweenSequenceItem<float>(
-                        tween: new Tween<T>(
+                        tween: new FloatTween(
-                    new TweenSequenceItem<T>(
+                    new TweenSequenceItem<float>(
-                        tween: new Tween<T>(
+                        tween: new FloatTween(
                           begin: peak,
                           end: end
                         ).chain(new CurveTween(curve: secondCurve))
         }
         
+        public static Animation<Offset> _getOffsetEmphasizedEasingAnimation(
+          Offset begin,
+          Offset peak,
+          Offset end,
+          bool isForward,
+          Animation<float> parent
+        ) {
+          Curve firstCurve;
+          Curve secondCurve;
+          float firstWeight;
+          float secondWeight;
+
+          if (isForward) {
+            firstCurve = _kAccelerateCurve;
+            secondCurve = _kDecelerateCurve;
+            firstWeight = _kPeakVelocityTime;
+            secondWeight = 1.0f - _kPeakVelocityTime;
+          } else {
+            firstCurve = _kDecelerateCurve.flipped;
+            secondCurve = _kAccelerateCurve.flipped;
+            firstWeight = 1.0f - _kPeakVelocityTime;
+            secondWeight = _kPeakVelocityTime;
+          }
+
+          return new TweenSequence<Offset>(
+            new List<TweenSequenceItem<Offset>>{
+              new TweenSequenceItem<Offset>(
+                weight: firstWeight,
+                tween: new OffsetTween(
+                  begin: begin,
+                  end: peak
+                ).chain(new CurveTween(curve: firstCurve))
+              ),
+              new TweenSequenceItem<Offset>(
+                weight: secondWeight,
+                tween: new OffsetTween(
+                  begin: peak,
+                  end: end
+                ).chain(new CurveTween(curve: secondCurve))
+              ),
+            }
+          ).animate(parent);
+        }
+        
+        
         public static float _getPeakPoint(float begin, float end) {
           return begin + (end - begin) * _kPeakVelocityProgress;
         }
 
   Animation<float> _getWidthAnimation(float screenWidth) {
     if (_controller.status == AnimationStatus.forward) {
-      return new Tween<float>(begin: _width, end: screenWidth).animate(
+      return new FloatTween(begin: _width, end: screenWidth).animate(
         new CurvedAnimation(
           parent: _controller.view,
           curve: new Interval(0.0f, 0.3f, curve: Curves.fastOutSlowIn)
-      return expanding_buttom_sheetUtils._getEmphasizedEasingAnimation(
+      return expanding_buttom_sheetUtils._getFloatEmphasizedEasingAnimation(
         begin: _width,
         peak: expanding_buttom_sheetUtils._getPeakPoint(begin: _width, end: screenWidth),
         end: screenWidth,
 
   Animation<float> _getHeightAnimation(float screenHeight) {
     if (_controller.status == AnimationStatus.forward) {
-      return expanding_buttom_sheetUtils._getEmphasizedEasingAnimation(
+      return expanding_buttom_sheetUtils._getFloatEmphasizedEasingAnimation(
         begin: expanding_buttom_sheetUtils._kCartHeight,
         peak: expanding_buttom_sheetUtils._kCartHeight + (screenHeight - expanding_buttom_sheetUtils._kCartHeight) * expanding_buttom_sheetUtils._kPeakVelocityProgress,
         end: screenHeight,
     } else {
-      return new Tween<float>(
+      return new FloatTween(
         begin: expanding_buttom_sheetUtils._kCartHeight,
         end: screenHeight
       ).animate(
   // Animation of the cut corner. It's cut when closed and not cut when open.
   Animation<float> _getShapeAnimation() {
     if (_controller.status == AnimationStatus.forward) {
-      return new Tween<float>(begin: expanding_buttom_sheetUtils._kCornerRadius, end: 0.0f).animate(
+      return new FloatTween(begin: expanding_buttom_sheetUtils._kCornerRadius, end: 0.0f).animate(
         new CurvedAnimation(
           parent: _controller.view,
           curve: new Interval(0.0f, 0.3f, curve: Curves.fastOutSlowIn)
-      return expanding_buttom_sheetUtils._getEmphasizedEasingAnimation(
+      return expanding_buttom_sheetUtils._getFloatEmphasizedEasingAnimation(
         begin: expanding_buttom_sheetUtils._kCornerRadius,
         peak: expanding_buttom_sheetUtils._getPeakPoint(begin: expanding_buttom_sheetUtils._kCornerRadius, end: 0.0f),
         end: 0.0f,
   }
 
   Animation<float> _getThumbnailOpacityAnimation() {
-    return new Tween<float>(begin: 1.0f, end: 0.0f).animate(
+    return new FloatTween(begin: 1.0f, end: 0.0f).animate(
       new CurvedAnimation(
         parent: _controller.view,
         curve: _controller.status == AnimationStatus.forward
 
   // Builder for the hide and reveal animation when the backdrop opens and closes
   Widget _buildSlideAnimation(BuildContext context, Widget child) {
-    _slideAnimation = expanding_buttom_sheetUtils._getEmphasizedEasingAnimation(
+    _slideAnimation = expanding_buttom_sheetUtils._getOffsetEmphasizedEasingAnimation(
       begin: new Offset(1.0f, 0.0f),
       peak: new Offset(expanding_buttom_sheetUtils._kPeakVelocityProgress, 0.0f),
       end: new Offset(0.0f, 0.0f),
   }
 
   Widget _buildThumbnail(BuildContext context, int index, Animation<float> animation) {
-     Animation<float> thumbnailSize = new Tween<float>(begin: 0.8f, end: 1.0f).animate(
+     Animation<float> thumbnailSize = new FloatTween(begin: 0.8f, end: 1.0f).animate(
       new CurvedAnimation(
         curve: new Interval(0.33f, 1.0f, curve: Curves.easeIn),
         parent: animation

Samples/UIWidgetsSamples_2019_4/Assets/UIWidgetsGallery/demo/shrine/login.cs

             new Column(
               children: new List<Widget>
               {
-                Image.asset("packages/shrine_images/diamond.png"),
+                Image.file("shrine_images/diamond.png"),
                 new SizedBox(height: 16.0f),
                 new Text(
                   "SHRINE",