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DataFormComboBoxField grayed out RSS

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Last post Jun 03, 2009 09:51 PM by davidezordan

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pyt

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DataFormComboBoxField grayed out

May 12, 2009 11:03 PM | LINK
I'm having problems getting the DataFormComboBoxField control to work in my form.

I cannot figure out why the drop-down is always disabled.

Here is the xaml:
```
<dataform:DataFormComboBoxField Binding="{Binding CompanyID, Mode=TwoWay, Converter={StaticResource idToCompanyConverter}}"
                                DisplayMemberPath="Name" />
```
The CompanyID property is a Guid. The dataform is in AutoEdit.

I assign a list of companies to the drop down's ItemsSource in the UserControl constructor.

What am I missing?

Thanks,

Pierre-Yves Troel

Ayuda Media Systems
Pierre-Yves Troel
Ayuda Media Systems
http://www.ayudasystems.com
StefanOlson

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Re: DataFormComboBoxField grayed out

May 13, 2009 01:02 AM | LINK

I presume that the CompanyID property has a publicly accessible setter? Are there any metadata attributes on the CompanyID property?

...Stefan

http://www.olsonsoft.com/blogs/stefanolson

pyt

Member

35 Points

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Re: DataFormComboBoxField grayed out

May 13, 2009 01:57 PM | LINK

It does indeed, here is the code for the property, it's from the auto-generated file:

        [DataMember()]
        public Guid CompanyID
        {
            get
            {
                return this._companyID;
            }
            set
            {
                if ((this._companyID != value))
                {
                    this.ValidateProperty("CompanyID", value);
                    this.RaiseDataMemberChanging("CompanyID");
                    this._companyID = value;
                    this.RaiseDataMemberChanged("CompanyID");
                }
            }
        }

I wrote a small routine to find the combo in the dataform by inspecting the VisualTree and I can see that the IsEnabled property is set to false on the Combo:

I tried to find what was bound to the property using GetBindingExpression(Control.IsEnabledProperty) but it returns null...

Pierre-Yves Troel

Ayuda Media Systems

http://www.ayudasystems.com

Pierre-Yves Troel
Ayuda Media Systems
http://www.ayudasystems.com

StefanOlson

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260 Points

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Re: DataFormComboBoxField grayed out

May 15, 2009 12:48 AM | LINK

If you look in the source code for the DataFormComboBoxField, using.net reflector, you can see, that IsEnabled is set when the combo box is constructed:
private ComboBox GenerateComboBox(bool isReadOnly) {
ComboBox box = new ComboBox {IsEnabled = !isReadOnly};

isReadOnly comes from these functions:
internal virtual bool EffectiveIsEditModeReadOnly { get; }
internal virtual bool EffectiveIsReadOnly { get; }

So, I think for some reason the data form field thinks that the property is read-only. Exactly why this happens, I'd have to substantially more investigation, but I do wonder whether it has to do with the use of a converter?

...Stefan

http://www.olsonsoft.com/blogs/stefanolson
NickVerschueren

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Re: DataFormComboBoxField grayed out

May 16, 2009 09:03 PM | LINK
Hi Pierre-Yves,

I've had the exact same problem as you and it's been driving me up the wall for a whole week now. Then today I stumbled across the answer: the DataFormComboBox gets disabled when it is bound to a property of type System.Guid. I think the is a pretty fundamental bug as we use Guids allmost exclusively as foreign keys in our databses.

Luckily I've also found an easy way around this problem: you can define an additional property in a partial class (in the Silverlight project if you're using RIA Services) to accompany your Entity.
For the parent entity this could look something like this:
```
namespace MyProject.Web
{
    public sealed partial class Customer
    {
        public string StringCustomerID
        {
            get { return this.CustomerID != null ? this.CustomerID.ToString() : null; }
        }
    }
}
```
For the child entity you will need to add a setter aswell:
```
namespace MyProject.Web
{
    public sealed partial class Order
    {
        public string StringUserID 
        {
            get { return this.UserID != null ? this.UserID.ToString() : null; }
            set { this.UserID = value != null ? new Guid(value): Guid.Empty; }
        }
    }
}
```
This fixed it for me, so I hope it will do the same for you.
Nick Verschueren - Euricom
.Net RIA Services silverlight RIA RIA Services LINQ - Entities Ria Services databinding .NET RIA Services shared silverlight

Nick Verschueren - Euricom
pyt

Member

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Re: DataFormComboBoxField grayed out

May 16, 2009 10:18 PM | LINK

Thanks a lot for the workaround, hopefully this will get fixed in the release.

Pierre-Yves Troel
Ayuda Media Systems
http://www.ayudasystems.com
glasin

Member

9 Points

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Re: DataFormComboBoxField grayed out

May 19, 2009 06:30 AM | LINK

I come across the same problem too, except mine is binded to an entity with a string as FK behind it. I would thought this be a very typical use case for any type table attribute. The code looks up the type table for a list of possible collection and the UI display them in a combo box.
The dataForm is binded to Assessment entity, Assessment Type is one of its property. I bind the comboBox ItemsSource in code behind because I cant figure out how to do this in the xaml itself.
[Association("AssessmentType_Assessment", "AssesmentTypeID", "AssessmentTypeID", IsForeignKey=true)]
[Bindable(true, BindingDirection.TwoWay)]
public AssessmentType AssessmentType

<df:DataFormComboBoxField Binding="{Binding AssessmentType, Mode=TwoWay, Converter={StaticResource assessmentTypeConverter}}" />

assessmentTypeField.ItemsSource = myGradeBookContext.AssessmentTypes.Select(a => a.AssessmentTypeID);
NickVerschueren

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16 Points

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Re: DataFormComboBoxField grayed out

May 19, 2009 10:39 AM | LINK

The issue here is that in the binding you're specifying the entity rather than the foreign key field. You shoud change the binding to:

Binding="{Binding AssessmentTypeID, Mode=TwoWay, Converter={StaticResource assessmentTypeConverter}}" />

When you change the AssessmentTypeID which is definded in the association on the entity, the related entity will automatically change along with it, so you do not need to bind the entity itself.

Upto now I have found no other way than to set the itemsource on the combobox in code, at least no other way that works ;) The problem is that the load of entities is asynchronous and the refresh of listitems is not automatic, so you need to handle the loaded event on the context in order to fill the dropdown list.

Another thing I've found is that when you change the partent entity in thes way other controls in the app don't seem to get notified of this, so if you have another control displaying for instance the details of your selected AssessmentType entity, you will need to update them yourself (for instance by resetting the itemsource)

Nick Verschueren - Euricom
RogerGu

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Re: DataFormComboBoxField grayed out

Jun 02, 2009 11:15 PM | LINK

Can I ask you two to share how you are setting the ItemssSource for the DataFormComboBoxField?

Thanks,

DataFormComboBoxField ItemsSource

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davidezordan

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Re: Re: DataFormComboBoxField grayed out

Jun 03, 2009 09:51 PM | LINK

@Roger: I've replied here http://silverlight.net/forums/p/94171/218171.aspx#218171

Thanks, Davide

Silverlight MVP

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DataFormComboBoxField grayed out RSS

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pyt