Programming with .NET - General

Re: Enum as DepedencyProperty

rankorn — Wed, 14 Oct 2009 10:08:19 GMT

In SL3, you do not even have to use TypeConverter as it automatically handles enums. I am not sure about intellisense.

Re: Enum as DepedencyProperty

DJanjicek — Fri, 24 Apr 2009 16:49:15 GMT

It works! Still a pity that IntelliSense doesn't work...

Anyways, thank you!

Re: Enum as DepedencyProperty

DMW — Fri, 24 Apr 2009 16:30:39 GMT

No, absolutely not. You can expose a single DP, whose type is the type of the enum. Then you will be able to set the value of that property to any of the values of the enum.

Re: Enum as DepedencyProperty

DJanjicek — Fri, 24 Apr 2009 15:53:14 GMT

Okay, so i have to create for every enum value a property?

Re: Enum as DepedencyProperty

DMW — Fri, 24 Apr 2009 09:06:34 GMT

In the call to DependencyProperty.Register, make sure that the last parameter reads something like this new PropertyMetadata( Foo.A ) assuming that you have an enum called Foo, with a named value A.

Re: Enum as DepedencyProperty

DJanjicek — Fri, 24 Apr 2009 06:33:41 GMT

dmw:
A further thought has crossed my mind. A common mistake to make when registering DPs is to leave in the default PropertyMetadata(0) in the DP.Register method. This will result in a TypeInitializationException at runtime, and potentially strange problems at design-time. Make sure that you change this to a proper value of the enum, as the PropertyMetadata constructor takes a parameter of type object. Thus boxing will occur, and unboxing an Int32 to an enum will fail during type initialization.

I don't understand this one... Could you provide an example?

Re: Enum as DepedencyProperty

DMW — Fri, 24 Apr 2009 02:11:47 GMT

A further thought has crossed my mind. A common mistake to make when registering DPs is to leave in the default PropertyMetadata(0) in the DP.Register method. This will result in a TypeInitializationException at runtime, and potentially strange problems at design-time. Make sure that you change this to a proper value of the enum, as the PropertyMetadata constructor takes a parameter of type object. Thus boxing will occur, and unboxing an Int32 to an enum will fail during type initialization.

Re: Enum as DepedencyProperty

DMW — Fri, 24 Apr 2009 02:06:37 GMT

DJanjicek:
i doubt the MS guys have written a converter for every particular enum they're using

Your are quite correct; they have not. The XAML parser can automatically parse strings to named enum values, and if you examine an enum-based property in Blend, you will see that it automatically displays a drop-down for the property. You therefore do not need to use a TypeConverter, and doing so will achieve little for a simple enum. I'm not denying that you might have had problems, but a TypeConverter is not the solution to them.

Re: Enum as DepedencyProperty

DJanjicek — Thu, 23 Apr 2009 20:09:23 GMT

I'll post the c# version tomorrow! Thanks for your effort!

Re: Enum as DepedencyProperty

wjchristenson2 — Thu, 23 Apr 2009 19:58:31 GMT

Below is a generic EnumTypeConverter class i wrote.

Here's a property using it:

    <TypeConverter(GetType(EnumTypeConverter(Of Vehicle.VehicleType)))> _
    Public Property Type() As VehicleType
        Get
            Return DirectCast(GetValue(Vehicle.TypeProperty), VehicleType)
        End Get
        Set(ByVal value As VehicleType)
            SetValue(Vehicle.TypeProperty, value)
        End Set
    End Property

Here is the generic EnumTypeConverter:

Imports System.ComponentModel

Public Class EnumTypeConverter(Of T)
    Inherits TypeConverter

    Public Overrides Function CanConvertFrom(ByVal context As System.ComponentModel.ITypeDescriptorContext, ByVal sourceType As System.Type) As Boolean
        If sourceType.Equals(GetType(String)) Then
            Return True
        Else
            Return MyBase.CanConvertFrom(context, sourceType)
        End If
    End Function

    Public Overrides Function CanConvertTo(ByVal context As System.ComponentModel.ITypeDescriptorContext, ByVal destinationType As System.Type) As Boolean
        If destinationType.Equals(GetType(String)) Then
            Return True
        Else
            Return MyBase.CanConvertTo(context, destinationType)
        End If
    End Function

    Public Overrides Function ConvertFrom(ByVal context As System.ComponentModel.ITypeDescriptorContext, ByVal culture As System.Globalization.CultureInfo, ByVal value As Object) As Object
        If TypeOf value Is String Then
            Try
                Return CType([Enum].Parse(GetType(T), value, True), T)
            Catch
                Throw New InvalidCastException(value)
            End Try
        Else
            Return MyBase.ConvertFrom(context, culture, value)
        End If
    End Function

    Public Overrides Function ConvertTo(ByVal context As System.ComponentModel.ITypeDescriptorContext, ByVal culture As System.Globalization.CultureInfo, ByVal value As Object, ByVal destinationType As System.Type) As Object
        If destinationType.Equals(GetType(String)) Then
            Return value.ToString()
        Else
            Return MyBase.ConvertTo(context, culture, value, destinationType)
        End If
    End Function
End Class

Re: Enum as DepedencyProperty

DJanjicek — Thu, 23 Apr 2009 16:52:31 GMT

I've found this article on the net, maybe it can be used to extend your implementation...

http://www.kindblad.com/2008/08/18/how-to-convert-from-string-to-enum-using-c-and-generics/

Re: Enum as DepedencyProperty

wjchristenson2 — Thu, 23 Apr 2009 16:41:21 GMT

I'm sure you could create a generic enum converter. M$ may have one out there that I'm not aware of. I've not done a lot of searching on it. Please post if you find one.

Re: Enum as DepedencyProperty

DJanjicek — Thu, 23 Apr 2009 16:28:03 GMT

Thank you very much, i will try that tomorrow! i'm just curious, your solution dictates to have a particular converter for every enum i will work with. How much work would it be to implement a generic converter? If i look at all the out-of-the-box controls which actually use enums for their properties i doubt the MS guys have written a converter for every particular enum they're using.

Re: Enum as DepedencyProperty

wjchristenson2 — Thu, 23 Apr 2009 16:17:24 GMT

You will need to create a TypeConverter for your property so that it will know how to convert from a string to your enumerated type. I wrote a quick demo for you on my blog. The link is below:

http://www.mostlydevelopers.com/blog/post/2009/04/23/Set-an-Enum-Dependency-Property-with-XAML.aspx

Enum as DepedencyProperty

DJanjicek — Thu, 23 Apr 2009 14:54:18 GMT

HI,

can somebody tell me how to register a dependency property of type enum? My property is accessable in xaml, but not how you would expect from an enum (drop down, etc). And the runtime throws a weird exception which doesn't make much sense...

Thanks in advance...