Business Forms in Silverlight Part 2

(this is a continuation of Part 1)

From the previous post:

Basic DataForm experience

Basic DataForm experience

The first problem is the OrderDate is unintialized and renders as 0/00/0000.

The first thought is to change the OrderDate from DateTime to Nullable<DateTime>. This will require either the database schema be changed, or a second viewmodel created. Changing the database schema just to support a user-interface tweak is obviously out of the question. However, writing a viewmodel and copying all the properties over breaks a rule of “DRY” (Don’t Repeat Yourself).

Luckily, XAML binding supports the notion of binding converters. This lets us transforms inputs from one type to another.

public class NullValueConverter : IValueConverter

    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        if (value is DateTime && targetType == typeof(Nullable<DateTime>))
            if ((DateTime)value == DateTime.MinValue)
                return null;
        return value;

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        return value;

Applying the converter to the date picker, we get reasonably good results. For example, after entering a date and then clearing it, we get a validation error showing (see picture below). Furthermore, hitting cancel restores the control back to default value.


This done, we are ready to tackle our next problem.


Here’s a sample of how converters are applied.

    <local:NullValueConverter x:Key="NullValueConverter" />
  <sdk:DataField Label="Order Date">
    <sdk:DatePicker SelectedDate="{Binding OrderDate, Converter={StaticResource NullValueConverter}}" />

Fool-Proof Business Forms in Silverlight Part I

Silverlight DataForms makes it quick and easy to get started with database applications. However, it has some downsides. The default isn’t particularly customizable, and to do anything more takes a great deal more effort.

Take the following example:

        internal sealed class OrderMetadata

            // Metadata classes are not meant to be instantiated.
            private OrderMetadata()

            [Display(Name = "Order date", GroupName = "Order", Order = 1)]
            public DateTime OrderDate { get; set; }

            [Range(0, 100.0, ErrorMessage = "Please enter more than $0.00")]
            [Display(Name = "Total Amount", GroupName = "Order", Order = 2)]
            public decimal Amount { get; set; }

            [Display(Name = "Purchase Order No", GroupName = "Order", Order = 3)]
            public string PurchaseOrder { get; set; }

            [Display(Name = "Customer Name", GroupName = "Customer", Order = 1)]
            public Customer Customer { get; set; }

            [Display(Name = "Is Delivered", GroupName = "Customer", Order = 2)]
            public byte[] IsDelivered { get; set; }

            public int CustomerId { get; set; }

            public int OrderId { get; set; }
            public float Weight { get; set; }

            [UIHint("Image", "SL", "ScannedFilename")]
            public Byte[] ScannedImage { get; set; }

            public String ScannedFilename { get; set; }

This generates a data form that gets us pretty close. See the picture below.


However, there are several issues:

  1. The Order date is very ugly. It should have default to a null value
  2. The Customer field should have been bound to a combo box or something more custom
  3. The Total Amount validation message could not be customized. It reports “Input is not in the correct format”. Ideally, the message should be customizable and localizable.
  4. CustomerId and OrderId should be hidden
  5. Scanned file name and Scanned image should be combined into a single image control, showing the image, the file name, and provide a method to replace the image.

Over the next few posts, I’ll discuss how to overcome these problems using a custom view model and avoid unnecessary code duplication.

Syncfusion’s latest datagrid

I’ve been looking forward to Syncfusion’s latest release of their Silverlight components (and it’s out today). In particular, their new SfDataGrid datagrid is reaching maturity so I decided to take it out for a quick spin, and verdict is out. Two thumbs up. Well done. Their API is intuitive and much improved from their original DataGrid. It is different, so don’t expect to be able to port over existing code easily, but there is considerably less code to port.

We’ll start off with a simple model

namespace SyncfusionGridDemo.ViewModels
    using System.ComponentModel.DataAnnotations;

    public class Customer
        [Display(Name="Full Name")]
        [Required(ErrorMessage="{0} is required")]
        public string FullName { get; set; }

        [Range(18, 80)]
        public int Age { get; set; }

As you can see there is not much to it, and we’ll create a viewmodel and host a collection of Customers.

namespace SyncfusionGridDemo.ViewModels
    using System.Collections.Generic;
    using System.Collections.ObjectModel;
    using System.Collections.Specialized;

    public class MainPageViewModel
        private IList<Customer> _addedCustomers = new List<Customer>();
        private IList<Customer> _deletedCustomers = new List<Customer>();

        public MainPageViewModel()
            Customers = new ObservableCollection<Customer>(new[]
                new Customer { FullName = "Marcus Aurelius", Age=30 },
                new Customer { FullName = "Dana Fausbinder", Age=3 },
                new Customer { FullName = "Tomoko Cressida McManus", Age=54 },
            Customers.CollectionChanged += Customers_CollectionChanged;

        void Customers_CollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
            switch (e.Action)
                case NotifyCollectionChangedAction.Add:
                    // TODO these will need to be saved to the database
                case NotifyCollectionChangedAction.Remove:
                case NotifyCollectionChangedAction.Replace:
                    // TODO these will need to be saved to the database



        public ObservableCollection<Customer> Customers { get; set; }

    public static class CollectionExtension
        public static void AddRange<T>(this IList<T> coll, IEnumerable<T> items)
            foreach (var item in items)
                if (!coll.Contains(item))

        public static void RemoveRange<T>(this IList<T> coll, IEnumerable<T> items)
            foreach (var item in items)
                if (coll.Contains(item))


And now let’s bind to Syncfusion SfDataGrid

             ItemsSource="{Binding Customers}" 

and the result is rather good for so little work.

Some minor criticism

The datagrid is not aware of IEditableObject interface. This interface supports BeginEdit(), EndEdit() and CancelEdit(). This allows the user to revert the record’s changes using the escape key.

Overall, the user experience is much improved. Thanks again for listening to my concerns.

Succeeding with Windows Phone Apps

Take aways:

  1. Add all screenshots
  2. Provide background image – or it will not get featured in the Store
  3. Description is super important especially the first few sentences

Make use of

  1. Live Tiles
  2. Lock Screen
  3. Toast Notification
  4. SkyDrive
  5. Wallet
  6. Caching
  7. Location Services

Live Tiles

  1. 159 x 169
  2. 336 x 336
  3. 691 x 336

There are three type of templates

  1. Flips to the back. So the most important info should be on the front
  2. Cycle template of 9 images – but don’t make user wait.
  3. Iconic template small icons
    1. 110×110 for small
    2. 202 x 202 for Medium.
    3. Wide uses the small icon

Effective Design-Time data with Silverlight

There were quite a few ways one can enable Silverlight design time data binding. Design time data binding provides the GUI designer with some sample values and this is particularly handy when laying out controls in Visual Studio.

Using d:DataContext and d:DesignInstance

<Grid x:Name="LayoutRoot" Background="White"

Note: You can also do this:

<Grid x:Name="LayoutRoot" Background="White"

Using d:DesignData


Note: the Build action should be DesignData or DesignDataWithDesignTimeCreatableTypes

Using d:DesignSource (for CollectionViewSource)

If your model binds to a CollectionViewSource, you can set it in conjunction with DesignInstance.

<CollectionViewSource x:Key="CustomerViewSource"
   local:Customer, CreateList=True}" /> 

MEF, Caliburn and loading xap files

This the following modification to MefBootstrapper allows us to load XAPs at runtime, and register the types with Caliburn.Micro so that it can locate the correct view for a given view model.

using Caliburn.Micro;

namespace SlCaliburnTest
    using Extensions;
    using System;
    using System.Collections.Generic;
    using System.ComponentModel.Composition;
    using System.ComponentModel.Composition.Hosting;
    using System.ComponentModel.Composition.Primitives;
    using System.ComponentModel.Composition.ReflectionModel;
    using System.Linq;
    using System.Threading.Tasks;

    public class MefBootstrapper : Bootstrapper<IShell>
        private CompositionContainer container;

        protected override void Configure()
            container = CompositionHost.Initialize(
                new AggregateCatalog(
                    AssemblySource.Instance.Select(x => new AssemblyCatalog(x)).OfType<ComposablePartCatalog>()

            var batch = new CompositionBatch();

            batch.AddExportedValue<IWindowManager>(new WindowManager());
            batch.AddExportedValue<IEventAggregator>(new EventAggregator());


        protected override object GetInstance(Type serviceType, string key)
            string contract = string.IsNullOrEmpty(key) ? AttributedModelServices.GetContractName(serviceType) : key;
            var exports = container.GetExportedValues<object>(contract);

            if (exports.Count() > 0)
                return exports.First();

            throw new Exception(string.Format("Could not locate any instances of contract {0}.", contract));

        protected override IEnumerable<object> GetAllInstances(Type serviceType)
            return container.GetExportedValues<object>(AttributedModelServices.GetContractName(serviceType));

        protected override void BuildUp(object instance)

        #region Xap

        public async Task<bool> AddXap(Uri uri)
            var catalog = (container.Catalog as AggregateCatalog);
            DeploymentCatalog deploymentCatalog;
            lock (catalog.Catalogs)
                if (catalog.Catalogs.Any(c => (c is DeploymentCatalog && (c as DeploymentCatalog).Uri == uri)))
                    return false;

                deploymentCatalog = new DeploymentCatalog(uri);
                deploymentCatalog.Changing += (s, e) =>
                    // It is necessary to Update AssemblySource before deploymentCatalog Changed is fired.
                    // 1. deploymentCatalog.Changed even triggers Recomposition, 
                    // 2. Recomposition triggers ViewLocator to load the View
                    // 3. ViewLocator uses AssemblySource to find the assembly the view belongs to.
            var downloadSuccess = await deploymentCatalog.Download();
            return downloadSuccess;

        private void UpdateAssemblySource(IEnumerable<ComposablePartDefinition> parts)
            var assemblies = from assembly in 
                                  (from p in parts
                                   select ReflectionModelServices.GetPartType(p).Value.Assembly)
                              where !AssemblySource.Instance.Contains(assembly)
                              select assembly;                             
            foreach (var assembly in assemblies.Distinct())


Syncfusion DataGrid – prevent automatic sorting after edit

There are two ways to prevent a Syncfusion DataGrid control from reordering your grid after you modify an item.

  1. Disable sorting after edits
    dataGrid1.ModelLoaded += (sender, eventArgs) =>
        dataGrid1.Model.TableProperties.SortingOptions = 
  2. Change the ActivateCurrentCellBehavior to SetCurrent
            <s:GridDataControl ItemsSource="{Binding EquipmentParts}" 
                                ActivateCurrentCellBehavior="SetCurrent"   />

Elmah Logging Full Stack Trace of WCF DomainServiceFault


By default, only a partial stack trace is logged to Elmah when a WCF Exception occurs. This is not helpful when trying to troubleshoot problems.


Elmah logs exception.ToString() – which in the case of a DomainServiceFault, only contains partial stack trace.


The solution is to wrap the exception in another one so that we can override ToString().

''' File: ElmahWcfExtensions
''' Usage: Decorate the DomainService with ServiceErrorBehavior and ServiceBehavior(IncludeExceptionDetailInFaults:=True)
''' Example:
'''    <ServiceModel.ServiceBehavior(IncludeExceptionDetailInFaults:=True)>
'''    <RequiresAuthentication()> _
'''    <EnableClientAccess()> _
'''    <ServiceErrorBehaviour(GetType(HttpErrorHandler))>
'''    Public Class SamDomainService

Option Compare Binary
Option Infer On
Option Strict On
Option Explicit On

Imports System
Imports System.Collections.Generic
Imports System.Collections.ObjectModel
Imports System.ServiceModel
Imports System.ServiceModel.Description
Imports System.ServiceModel.Dispatcher
Imports System.ServiceModel.Channels

Namespace Web

    ''' <summary>
    ''' Your handler to actually tell ELMAH about the problem.
    ''' </summary>
    Public Class HttpErrorHandler
        Implements IErrorHandler

        Public Sub ProvideFault([error] As Exception, version As MessageVersion, ByRef fault As Message) Implements IErrorHandler.ProvideFault
            If [error] IsNot Nothing Then
                ' Notify ELMAH of the exception.
                If System.Web.HttpContext.Current Is Nothing Then
                    Dim elmahCon As Elmah.ErrorLog = Elmah.ErrorLog.GetDefault(Nothing)
                    elmahCon.Log(New Elmah.Error([error]))
                    Elmah.ErrorSignal.FromCurrentContext().Raise(ServiceFault.From([error]), System.Web.HttpContext.Current)
                End If
            End If
        End Sub

        Public Function HandleError([error] As Exception) As Boolean Implements IErrorHandler.HandleError
            Return False
        End Function

    End Class

    ''' <summary>
    ''' So we can decorate Services with the [ServiceErrorBehaviour(typeof(HttpErrorHandler))]
    ''' ...and errors reported to ELMAH
    ''' </summary>
    Public Class ServiceErrorBehaviourAttribute
        Inherits Attribute
        Implements IServiceBehavior
        Private errorHandlerType As Type

        Public Sub New(errorHandlerType As Type)
            Me.errorHandlerType = errorHandlerType
        End Sub

        Public Sub Validate(description As ServiceDescription, serviceHostBase As ServiceHostBase) Implements IServiceBehavior.Validate

        End Sub

        Public Sub AddBindingParameters(description As ServiceDescription, serviceHostBase As ServiceHostBase, endpoints As Collection(Of ServiceEndpoint), parameters As BindingParameterCollection) Implements IServiceBehavior.AddBindingParameters
        End Sub

        Public Sub ApplyDispatchBehavior(description As ServiceDescription, serviceHostBase As ServiceHostBase) Implements IServiceBehavior.ApplyDispatchBehavior

            Dim errorHandler As IErrorHandler
            errorHandler = DirectCast(Activator.CreateInstance(errorHandlerType), IErrorHandler)
            For Each channelDispatcherBase As ChannelDispatcherBase In serviceHostBase.ChannelDispatchers
                Dim channelDispatcher As ChannelDispatcher = TryCast(channelDispatcherBase, ChannelDispatcher)
        End Sub

    End Class

    ''' <summary>
    ''' ServiceFault wrapper so that the entire stack trace is logged.
    ''' </summary>
    ''' <remarks></remarks>
    Public Class ServiceFault
        Inherits FaultException

        Friend _faultException As Exception
        Private Sub New(faultException As Exception)
            _faultException = faultException
        End Sub

        Public Shared Function From(faultException As Exception) As FaultException
            Return New ServiceFault(faultException)
        End Function

        Public Overrides ReadOnly Property Message As String
                Return _faultException.Message
            End Get
        End Property

        Public Overrides Property Source As String
                Return _faultException.Source
            End Get
            Set(value As String)
                MyBase.Source = value
            End Set
        End Property

        Public Overrides Function ToString() As String
            Dim faultExc As FaultException(Of DomainServiceFault) =
                TryCast(_faultException, FaultException(Of DomainServiceFault))

            If faultExc Is Nothing Then
                Return _faultException.StackTrace()
                ' DomainServiceFault stores its stacktrace in a 
                ' different location
                Return faultExc.Detail.StackTrace()
            End If
        End Function

    End Class
End Namespace