Silverlight 4-绑定不适用于POCO对象的枚举类型吗？

Question

I have a WCF RIA POCO object -> Traffic light which has an enum type describing it's state.

[DataContract]
public class TrafficLight
{
    [Key]
    [DataMember]
    public long Id { get; set; }    

    [DataMember]
    public Longitude Longitude { get; set; }

    [DataMember]
    public Latitude Latitude { get; set; }

    [DataMember]
    public TrafficLightState SelectedLight { get; set; }
}

[DataMember]
public enum TrafficLightState
{
    [EnumMember]
    Red = 0,

    [EnumMember]
    Yellow = 1,

    [EnumMember]
    Green = 2
}

So given a WCF RIA service I needed to get this traffic light object to the Silverlight client application:

public IEnumerable<TrafficLight> GetTrafficLightsForCity(int cityId)
{
    return Data.GetTrafficLightsForCity(cityId).AsEnumerable();
}

So that works fine. I get my list and all is good until I decide to bind the list to a grid that will display my traffic lights... (PS. This is a game kinda like sim city):

The way the traffic lights are displayed in the grid is via a small control that displays the state of the light -> red, yellow, green, plus some other stuff. For now I will just show you the Light status and ID:

<UserControl x:Name="MiniTrafficLightControl" x:Class="UI.MiniTrafficLight"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    d:DesignHeight="15" 
    d:DesignWidth="15"
    Width="15" Height="15">
    <StackPanel Orientation="Horizontal">
        <Border x:Name="BrdGreen" Visibility="Visible" CornerRadius="10" Width="15" Height="15" Margin="0" ToolTipService.ToolTip="Runing" d:IsLocked="True">
        <Border.Background>
            <RadialGradientBrush  GradientOrigin="0.4,0.3" Center="0.4,0.3" RadiusX="0.5" RadiusY="0.5">
            <RadialGradientBrush.GradientStops>
                <GradientStop Color="LightGreen" Offset="0" />
            <GradientStop Color="Green" Offset="0.95" />
            </RadialGradientBrush.GradientStops>
        </RadialGradientBrush>
        </Border.Background>
    </Border>
    <Border x:Name="BrdYellow" Visibility="Collapsed" CornerRadius="10" Width="15" Height="15" Margin="0" ToolTipService.ToolTip="Action Pending" d:IsHidden="True" d:IsLocked="True">
        <Border.Background>
            <RadialGradientBrush  GradientOrigin="0.4,0.3" Center="0.4,0.3" RadiusX="0.5" RadiusY="0.5">
            <RadialGradientBrush.GradientStops>
                <GradientStop Color="Yellow" Offset="0" />
            <GradientStop Color="Orange" Offset="0.95" />
            </RadialGradientBrush.GradientStops>
        </RadialGradientBrush>
        </Border.Background>
    </Border>
    <Border x:Name="BrdRed" Visibility="Collapsed" CornerRadius="10" Width="15" Height="15" Margin="0" ToolTipService.ToolTip="Stopped" d:IsHidden="True" d:IsLocked="True">
        <Border.Background>
            <RadialGradientBrush  GradientOrigin="0.4,0.3" Center="0.4,0.3" RadiusX="0.5" RadiusY="0.5">
            <RadialGradientBrush.GradientStops>
                <GradientStop Color="Orange" Offset="0" />
            <GradientStop Color="Red" Offset="0.95" />
            </RadialGradientBrush.GradientStops>
        </RadialGradientBrush>
        </Border.Background>
    </Border>
    </StackPanel>
</UserControl>

And the code behind for the control:

namespace UI
{
    public partial class MiniTrafficLight : UserControl
    {
        public static readonly DependencyProperty TrafficLightStateProperty = DependencyProperty.Register("TrafficLightState", typeof(TrafficLightState), typeof(MiniTrafficLight), null);

        public TrafficLightState TrafficLightState
    {
        get
        {
            return (TrafficLightState)this.GetValue(TrafficLightStateProperty);
        }
        set
        {
            if (value == TrafficLightState.Red)
        {
            this.BrdRed.Visibility = System.Windows.Visibility.Visible;
            this.BrdGreen.Visibility = System.Windows.Visibility.Collapsed;
            this.BrdYellow.Visibility = System.Windows.Visibility.Collapsed;
        }
        else if (value == TrafficLightState.Yellow)
        {
            this.BrdRed.Visibility = System.Windows.Visibility.Collapsed;
            this.BrdGreen.Visibility = System.Windows.Visibility.Collapsed;
            this.BrdYellow.Visibility = System.Windows.Visibility.Visible;
        }
        else
        {
             this.BrdRed.Visibility = System.Windows.Visibility.Collapsed;
                     this.BrdGreen.Visibility = System.Windows.Visibility.Visible;
             this.BrdYellow.Visibility = System.Windows.Visibility.Collapsed;
        }

                this.SetValue(TrafficLightStateProperty, value);
        }
        }
    }
}

so now the problem is that if anywhere on the page I have a grid that displays all traffic light objects using the MiniTraficLight control inside a grid - the MiniTrafficLight control never works... or it never displays the green red or yellow lights. I've debugged the service and have verified that the TrafficLightState property is set when its being read from the db for each traffic light object. I also can verify that on the client silverlight app that the TrafficLightState for each TrafficLight object arrives properly (aka... it is set).

However, if I set the MiniTrafficLight's control TrafficLightState manually without binding it works. If I use binding it never shows up. With or without a converter that property on the MiniTrafficLight control never gets called. The reason I know is that I added a MessageBox.Show(...) on the set accessor of the property and i don't see any message boxes. If I put break points - they never get reached. Bellow is the sample code that displays the Traffic Light objects inside a grid:

<datagrid:DataGrid x:Name="ReceiverNodesDataGrid" Grid.Row="1" AutoGenerateColumns="False" IsReadOnly="True" HorizontalAlignment="Stretch" SelectionMode="Single">
    <datagrid:DataGrid.Columns>
        <datagrid:DataGridTemplateColumn Header="Status">
            <datagrid:DataGridTemplateColumn.CellTemplate>
                <DataTemplate>
                    <local:MiniTraficLight TrafficLightState="{Binding TrafficLightState}"/>
        </DataTemplate>
            </datagrid:DataGridTemplateColumn.CellTemplate>
    </datagrid:DataGridTemplateColumn>
        <datagrid:DataGridTextColumn Header="Id" Binding="{Binding Id}" />
    </datagrid:DataGrid.Columns>
</datagrid:DataGrid>

Any idea why this binding doesn't work?

Thanks All, Martin

Answer 1

So apparently the trick to this is to properly implement the dependency properties. UGHHHHH!

namespace UI
{
    public partial class MiniTrafficLight : UserControl
    {
        private static PropertyMetaData trafficLightStateMetaData = new PropertyMetaData(new PropertyChangedCallBack(TrafficLightState_Changed));
        public static readonly DependencyProperty TrafficLightStateProperty = DependencyProperty.Register("TrafficLightState", typeof(TrafficLightState), typeof(MiniTrafficLight), trafficLightStateMetaData);

        public TrafficLightState TrafficLightState
        {
            get { return (TrafficLightState)this.GetValue(TrafficLightStateProperty); }
            set { this.SetValue(TrafficLightStateProperty, value); }
        }

        private static void TrafficLightState_Changed(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            MiniTrafficLight sender = d as MiniTrafficLight;
            TrafficLightState state = (TrafficLightState)e.NewState;

            if( state == TrafficLightState.Red )
            {
                //...
            }
            else if ( state == TrafficLightState.Yellow )
            {
                //...
            }
            else
            {
                //...
            }
        }
    }
}