Support for ErrorTemplate

.gitignore

@@ -11,3 +11,5 @@ src/Graphviz4Net.v12.suo
 .vs/slnx.sqlite
 src/.vs/Graphviz4Net/v15/.suo
 src/.vs/Graphviz4Net/v15/sqlite3/storage.ide
+.vs
+*.bak

src/Graphviz4Net.WPF.Example/Graphviz4Net.WPF.Example.csproj

@@ -116,6 +116,9 @@
     <Resource Include="Avatars\avatar3.jpg" />
     <Resource Include="Avatars\avatarAnon.gif" />
   </ItemGroup>
+  <ItemGroup>
+    <Resource Include="Assets\error.png" />
+  </ItemGroup>
   <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
   <!-- To modify your build process, add your task inside one of the targets below and uncomment it. 
        Other similar extension points exist, see Microsoft.Common.targets.

src/Graphviz4Net.WPF.Example/MainWindow.xaml

@@ -83,6 +83,13 @@
             <Path Data="{Binding Data}" Stroke="Black" StrokeThickness="1" ToolTip="{Binding Edge.Label}"/>
         </DataTemplate>
 
+        <DataTemplate x:Key="ErrorTemplate">
+            <StackPanel Orientation="Horizontal">
+                <Image Source="pack://application:,,,/Graphviz4Net.WPF.Example;component/Assets/error.png"/>
+                <TextBlock Text="{Binding ErrorMessage}" TextWrapping="Wrap" Width="300"/>
+            </StackPanel>
+        </DataTemplate>
+
         <ObjectDataProvider x:Key="dataFromLayoutEngineEnum" MethodName="GetValues"
                             ObjectType="{x:Type System:Enum}">
             <ObjectDataProvider.MethodParameters>
@@ -144,6 +151,7 @@
             <WPF:GraphLayout 
                 UseContentPresenterForAllElements="True"
                 LogGraphvizOutput="True"
+                ErrorTemplate="{StaticResource ErrorTemplate}"
                 Graph="{Binding Graph}"
                 Engine="{Binding LayoutEngine}"
                 x:Name="GraphLayout">

src/Graphviz4Net.WPF.Example/MainWindowViewModel.cs

@@ -148,6 +148,10 @@ public LayoutEngine LayoutEngine
 		public string UpdatePersonName { get; set; }
 
 		public string UpdatePersonNewName { get; set; }
+        public string DotExecutablePath
+        {
+            get { return @"C:\Program Files (x86)\Graphviz2.38\bin"; }
+        }
 
         public IEnumerable<string> PersonNames
         {

src/Graphviz4Net.WPF/GraphLayout.cs

@@ -9,6 +9,7 @@ namespace Graphviz4Net.WPF
     using Graphs;
 #if !SILVERLIGHT
     using System.Threading.Tasks;
+    using System.Windows.Data;
 #endif
 
     [TemplatePart(Name = "PART_Canvas", Type = typeof(Canvas))]
@@ -53,6 +54,13 @@ public class GraphLayout : Control
                 typeof(GraphLayout),
                 new PropertyMetadata(string.Empty));
 
+        public static readonly DependencyProperty ErrorTemplateProperty =
+           DependencyProperty.Register(
+               "ErrorTemplate",
+               typeof(DataTemplate),
+               typeof(GraphLayout),
+               new PropertyMetadata());
+
         private LayoutDirector director;
 
         private Exception backgroundException = null;
@@ -64,7 +72,7 @@ static GraphLayout()
         {
             DefaultStyleKeyProperty.OverrideMetadata(
                             typeof(GraphLayout),
-                            new FrameworkPropertyMetadata(typeof(GraphLayout)));                      
+                            new FrameworkPropertyMetadata(typeof(GraphLayout)));
         }
 #endif
 
@@ -135,6 +143,12 @@ public string DotExecutablePath
             set { this.SetValue(DotExecutablePathProperty, value); }
         }
 
+        public DataTemplate ErrorTemplate
+        {
+            get { return (DataTemplate)this.GetValue(ErrorTemplateProperty); }
+            set { this.SetValue(ErrorTemplateProperty, value); }
+        }
+
         public override void OnApplyTemplate()
         {
             base.OnApplyTemplate();
@@ -143,7 +157,7 @@ public override void OnApplyTemplate()
         }
 
         private static void OnUseContentPresenterForAllElementsChanged(
-            DependencyObject dependencyObject, 
+            DependencyObject dependencyObject,
             DependencyPropertyChangedEventArgs args)
         {
             var graphLayout = (GraphLayout)dependencyObject;
@@ -153,7 +167,7 @@ private static void OnUseContentPresenterForAllElementsChanged(
             }
             else
             {
-                graphLayout.elementsFactory = new DefaultLayoutElementsFactory();                
+                graphLayout.elementsFactory = new DefaultLayoutElementsFactory();
             }
         }
 
@@ -175,7 +189,7 @@ private void GraphChanged(object sender, GraphChangedArgs e)
         private void UpdateVerticesLayout()
         {
             if (this.canvas == null ||
-				this.Graph == null ||
+                this.Graph == null ||
                 DesignerProperties.GetIsInDesignMode(this))
             {
                 return;
@@ -217,13 +231,7 @@ private void UpdateVerticesLayout()
             }
             catch (Exception ex)
             {
-                var textBlock = new TextBlock { Width = 300, TextWrapping = TextWrapping.Wrap };
-                textBlock.Text =
-                    string.Format(
-                        "Graphviz4Net: an exception was thrown during layouting." +
-                        "Exception message: {0}.",
-                        ex.Message);
-                this.canvas.Children.Add(textBlock);
+                ShowError(ex);
             }
         }
 
@@ -255,14 +263,17 @@ private void BuildGraph()
 
         private void ShowError(Exception ex)
         {
-            var textBlock = new TextBlock { Width = 300, TextWrapping = TextWrapping.Wrap };
-            textBlock.Text =
-                string.Format(
+            var content = new ContentControl { ContentTemplate = ErrorTemplate, Width = 300 };
+            content.Content = new
+            {
+                ErrorMessage = string.Format(
                     "Graphviz4Net: an exception was thrown during layouting." +
                     "Exception message: {0}.",
-                    ex.Message);
+                    ex.Message),
+                Error = ex
+            };
             this.canvas.Children.Clear();
-            this.canvas.Children.Add(textBlock);
+            this.canvas.Children.Add(content);
         }
 
         private delegate void VoidDelegate();

src/Graphviz4Net.WPF/Themes/Generic.xaml

@@ -1,7 +1,12 @@
 <ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
                     xmlns:GraphvizWPF="clr-namespace:Graphviz4Net.WPF">
+
+    <DataTemplate x:Key="ErrorTemplateKey">
+        <TextBlock Text="{Binding ErrorMessage}" Width="300" TextWrapping="Wrap"/>
+    </DataTemplate>
     <Style TargetType="{x:Type GraphvizWPF:GraphLayout}">
+        <Setter Property="ErrorTemplate" Value="{StaticResource ErrorTemplateKey}"/>
         <Setter Property="Template">
             <Setter.Value>
                 <ControlTemplate TargetType="{x:Type GraphvizWPF:GraphLayout}">