Fix ProgressBar display.

Closes #217.

samples/BindingTest/MainWindow.paml

@@ -28,6 +28,7 @@
             <TextBlock FontSize="16" Text="Numeric Bindings"/>
             <TextBox Watermark="Double" UseFloatingWatermark="True" Text="{Binding Path=DoubleValue, Mode=TwoWay}"/>
             <TextBlock Text="{Binding Path=DoubleValue}"/>
+            <ProgressBar Maximum="10" Value="{Binding DoubleValue}"/>
           </StackPanel>
         </StackPanel>
       </StackPanel>

src/Perspex.Base/Utilities/TypeUtilities.cs

@@ -93,8 +93,16 @@ namespace Perspex.Utilities
             if ((value.GetType() == typeof(string) && Conversions.ContainsKey(to)) ||
                 (to == typeof(string) && Conversions.ContainsKey(value.GetType())))
             {
-                result = Convert.ChangeType(value, to, culture);
-                return true;
+                try
+                {
+                    result = Convert.ChangeType(value, to, culture);
+                    return true;
+                }
+                catch
+                {
+                    result = null;
+                    return false;
+                }
             }
             else
             {

src/Perspex.Controls/ProgressBar.cs

@@ -18,19 +18,32 @@ namespace Perspex.Controls
             ValueProperty.Changed.AddClassHandler<ProgressBar>(x => x.ValueChanged);
         }
 
+        /// <inheritdoc/>
+        protected override Size ArrangeOverride(Size finalSize)
+        {
+            UpdateIndicator(finalSize);
+            return base.ArrangeOverride(finalSize);
+        }
+
         /// <inheritdoc/>
         protected override void OnTemplateApplied()
         {
             _indicator = this.GetTemplateChild<Border>("PART_Indicator");
+            UpdateIndicator(Bounds.Size);
         }
 
-        private void ValueChanged(PerspexPropertyChangedEventArgs e)
+        private void UpdateIndicator(Size bounds)
         {
             if (_indicator != null)
             {
-                double percent = Maximum == Minimum ? 1.0 : ((double)e.NewValue - Minimum) / (Maximum - Minimum);
-                _indicator.Width = Bounds.Width * percent;
+                double percent = Maximum == Minimum ? 1.0 : (Value - Minimum) / (Maximum - Minimum);
+                _indicator.Width = bounds.Width * percent;
             }
         }
+
+        private void ValueChanged(PerspexPropertyChangedEventArgs e)
+        {
+            UpdateIndicator(Bounds.Size);
+        }
     }
 }