Fix GetDesiredSize (#87)

* Fix GetDesiredSize

* update for readability

src/Core/src/Handlers/View/ViewHandlerOfT.Tizen.cs

@@ -61,14 +61,9 @@ public override Size GetDesiredSize(double widthConstraint, double heightConstra
  {
  var nativeView = NativeView;
 
- if (nativeView == null || VirtualView == null)
+ if (nativeView == null || VirtualView == null || NativeParent == null)
  {
- return Size.Zero;
- }
-
- if (NativeParent == null)
- {
- return new Size(widthConstraint, heightConstraint);
+ return VirtualView == null ? Size.Zero : new Size(VirtualView.Width, VirtualView.Height);
  }
 
  int availableWidth = widthConstraint.ToScaledPixel();
@@ -79,9 +74,13 @@ public override Size GetDesiredSize(double widthConstraint, double heightConstra
  if (availableHeight < 0)
  availableHeight = int.MaxValue;
 
+ var explicitWidth = VirtualView.Width;
+ var explicitHeight = VirtualView.Height;
+ var hasExplicitWidth = explicitWidth >= 0;
+ var hasExplicitHeight = explicitHeight >= 0;
+
  Size measured;
- var nativeViewMeasurable = nativeView as IMeasurable;
- if (nativeViewMeasurable != null)
+ if (nativeView is IMeasurable nativeViewMeasurable)
  {
  measured = nativeViewMeasurable.Measure(availableWidth, availableHeight).ToDP();
  }
@@ -90,7 +89,8 @@ public override Size GetDesiredSize(double widthConstraint, double heightConstra
  measured = Measure(availableWidth, availableHeight);
  }
 
- return measured;
+ return new Size(hasExplicitWidth ? explicitWidth : measured.Width,
+ hasExplicitHeight ? explicitHeight : measured.Height);
  }
 
  public virtual ERect GetNativeContentGeometry()