Log invalid binding values in PriorityValue.

src/Perspex.Base/PerspexObject.cs

@@ -775,7 +775,11 @@ namespace Perspex
                 validate2 = v => validate(this, v);
             }
 
-            PriorityValue result = new PriorityValue(property.Name, property.PropertyType, validate2);
+            PriorityValue result = new PriorityValue(
+                property.Name, 
+                property.PropertyType, 
+                validate2,
+                _propertyLog);
 
             result.Changed.Subscribe(x =>
             {

src/Perspex.Base/PriorityValue.cs

@@ -7,6 +7,7 @@ using System.Linq;
 using System.Reactive.Subjects;
 using System.Text;
 using Perspex.Utilities;
+using Serilog;
 
 namespace Perspex
 {
@@ -54,19 +55,30 @@ namespace Perspex
         /// </summary>
         private readonly Func<object, object> _validate;
 
+        /// <summary>
+        /// An optional logger.
+        /// </summary>
+        private ILogger _logger;
+
         /// <summary>
         /// Initializes a new instance of the <see cref="PriorityValue"/> class.
         /// </summary>
         /// <param name="name">The name of the property.</param>
         /// <param name="valueType">The value type.</param>
         /// <param name="validate">An optional validation function.</param>
-        public PriorityValue(string name, Type valueType, Func<object, object> validate = null)
+        /// <param name="logger">An optional logger</param>
+        public PriorityValue(
+            string name, 
+            Type valueType,
+            Func<object, object> validate = null,
+            ILogger logger = null)
         {
             _name = name;
             _valueType = valueType;
             _value = PerspexProperty.UnsetValue;
             ValuePriority = int.MaxValue;
             _validate = validate;
+            _logger = logger;
         }
 
         /// <summary>
@@ -225,9 +237,13 @@ namespace Perspex
                 _value = value;
                 _changed.OnNext(Tuple.Create(old, _value));
             }
-            else
+            else if (_logger != null)
             {
-                // TODO: Log error.
+                _logger.Error(
+                    "Binding produced invalid value for {$Type} {$Property}: {$Value}",
+                    _valueType,
+                    _name,
+                    value);
             }
         }
 

tests/Perspex.Base.UnitTests/Perspex.Base.UnitTests.csproj

@@ -40,6 +40,14 @@
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
   <ItemGroup>
+    <Reference Include="Serilog, Version=1.5.0.0, Culture=neutral, PublicKeyToken=24c2f752a8e58a10, processorArchitecture=MSIL">
+      <HintPath>..\..\packages\Serilog.1.5.9\lib\net45\Serilog.dll</HintPath>
+      <Private>True</Private>
+    </Reference>
+    <Reference Include="Serilog.FullNetFx, Version=1.5.0.0, Culture=neutral, PublicKeyToken=24c2f752a8e58a10, processorArchitecture=MSIL">
+      <HintPath>..\..\packages\Serilog.1.5.9\lib\net45\Serilog.FullNetFx.dll</HintPath>
+      <Private>True</Private>
+    </Reference>
     <Reference Include="System" />
     <Reference Include="xunit.assert">
       <HintPath>..\..\packages\xunit.assert.2.0.0\lib\portable-net45+win+wpa81+wp80+monotouch+monoandroid+Xamarin.iOS\xunit.assert.dll</HintPath>

tests/Perspex.Base.UnitTests/packages.config

@@ -3,6 +3,7 @@
   <package id="Rx-Core" version="2.2.5" targetFramework="net45" />
   <package id="Rx-Interfaces" version="2.2.5" targetFramework="net45" />
   <package id="Rx-Linq" version="2.2.5" targetFramework="net45" />
+  <package id="Serilog" version="1.5.9" targetFramework="net45" />
   <package id="xunit" version="2.0.0" targetFramework="net45" />
   <package id="xunit.abstractions" version="2.0.0" targetFramework="net45" />
   <package id="xunit.assert" version="2.0.0" targetFramework="net45" />