User control's Dependency Property doesn't get bound in Silverlight

Question

I have created a user control like numeric updown as follows

 <StackPanel Orientation="Horizontal" VerticalAlignment="Top" >
    <TextBox x:Name="InputTextBox" Grid.Row="0" Grid.Column="0" Grid.RowSpan="1"
                Style="{StaticResource NumericUpDownTextBoxStyle}"

             KeyDown="InputTextBox_KeyDown" 
             KeyUp="InputTextBox_KeyUp"
             GotFocus="InputTextBox_GotFocus" 
             LostFocus="InputTextBox_LostFocus"  
             MouseWheel="InputTextBox_MouseWheel"
             MouseEnter="InputTextBox_MouseEnter"
             LayoutUpdated="InputTextBox_LayoutUpdated" 
             Text="{Binding Path=ControlValue, Mode=TwoWay,ValidatesOnDataErrors=True,ValidatesOnExceptions=True,NotifyOnValidationError=True}"/>
</StackPanel>

I have bind a ViewModel to this control where I Set ControlValue property to TextBox property of the user control template textbox.

Everthing works fine at a control level. I have exposed from usercontrol.

public static readonly DependencyProperty MaximumValueProperty;

public static readonly DependencyProperty MinimumValueProperty;

public static readonly DependencyProperty StepValueProperty;

public static readonly DependencyProperty TextValueProperty;

My Properties are

 public double Maximum
{
    get
    {
        return (double)GetValue(MaximumValueProperty);
    }
    set
    {
        SetValue(MaximumValueProperty, value);
        this.ViewModel.Maximum = this.Maximum;
    }
}

public double Minimum
{
    get
    {
        return (double)GetValue(MinimumValueProperty);
    }
    set
    {
        SetValue(MinimumValueProperty, value);
        this.ViewModel.Minimum = this.Minimum;
    }
}

public double Step
{
    get
    {
        return (double)GetValue(StepValueProperty);
    }
    set
    {
        SetValue(StepValueProperty, value);
        this.ViewModel.Step = this.Step;
    }
}

public double TextValue
{
    get
    {
        return (double)GetValue(TextValueProperty);
    }
    set
    {
        SetValue(TextValueProperty, value);
        this.ViewModel.ControlValue = Convert.ToString(value);
    }
}

Initialization of the property.

  static NumericUpDown()
    {
        MaximumValueProperty = DependencyProperty.Register("Maximum", typeof(double), typeof(NumericUpDown), new PropertyMetadata(null));
        MinimumValueProperty = DependencyProperty.Register("Minimum", typeof(double), typeof(NumericUpDown), new PropertyMetadata(null));
        StepValueProperty = DependencyProperty.Register("Step", typeof(double), typeof(NumericUpDown), new PropertyMetadata(null));
        TextValueProperty = DependencyProperty.Register("TextValue", typeof(double), typeof(NumericUpDown), new PropertyMetadata(null));
    }

My Usercontrol implementation in the MainPage.xaml page as follows

 <local:NumericUpDown Maximum="28" Minimum="-28" Step="0.25" TextValue="{Binding ElementName=FranePrice, Path=DataContext.FranePrice}"></local:NumericUpDown>

Where I have another ViewModel which i bind to the XAML page and there is a Property in the ViewModel which i bind to the TextValue property of the Usercontrol.

FramePrice is property in the View model that i bind to the TextValue property of the user control

and Main page XAML is

<UserControl x:Class="DatePicker.MainPage"
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"
xmlns:local="clr-namespace:DatePicker"
mc:Ignorable="d"
d:DesignHeight="300" d:DesignWidth="400" xmlns:sdk="http://schemas.microsoft.com/winfx/2006/xaml/presentation/sdk">

<Grid x:Name="LayoutRoot" Background="White">
    <StackPanel Orientation="Vertical">

        <local:NumericUpDown Maximum="28" Minimum="-28" Step="0.25" TextValue="{Binding ElementName=FranePrice, Path=DataContext.FranePrice}"></local:NumericUpDown>
        <Button Content="Show Date" Height="23" Name="button1" VerticalAlignment="Top" Width="75" Click="button1_Click"/>
    </StackPanel>
</Grid>

This View model of the page where i used user control. On click event i showing TextValue to user.

public class MainPageViewModel : EntityViewModel {

    public MainPageViewModel()
    {

    }
    private double framePrice;
    public Double FramePrice
    {
        get
        {
            return framePrice;
        }
        set
        {
            framePrice = value;
            PropertyChangedHandler("FramePrice");
        }
    }
}

When I change the TextValue in the User control it doesnot change in the FramePrice property of the page viewmodel.

Is anything wrong in the code.???

As per Luke Woodward's post I have updated code as follows

 public static readonly DependencyProperty MaximumValueProperty;
    public static readonly DependencyProperty MinimumValueProperty;
    public static readonly DependencyProperty StepValueProperty;
    public static readonly DependencyProperty TextValueProperty;

    public static double Max;
    public static double Min;
    public static double Stp;
    public static double Val;

  public double Maximum
    {
        get
        {
            return (double)GetValue(MaximumValueProperty);
        }
        set
        {
            SetValue(MaximumValueProperty, value);
        }
    }

    public double Minimum
    {
        get
        {
            return (double)GetValue(MinimumValueProperty);
        }
        set
        {
            SetValue(MinimumValueProperty, value);
        }
    }

    public double Step
    {
        get
        {
            return (double)GetValue(StepValueProperty);
        }
        set
        {
            SetValue(StepValueProperty, value);
        }
    }

    public double TextValue
    {
        get
        {
            return (double)GetValue(TextValueProperty);
        }
        set
        {
            SetValue(TextValueProperty, value);
        }
    }
  static NumericUpDown()
    {
        MaximumValueProperty = DependencyProperty.Register("Maximum", typeof(double), typeof(NumericUpDown), new PropertyMetadata(new PropertyChangedCallback(onMaximumValueChanged)));
        MinimumValueProperty = DependencyProperty.Register("Minimum", typeof(double), typeof(NumericUpDown), new PropertyMetadata(new PropertyChangedCallback(onMinimumValueChanged)));
        StepValueProperty = DependencyProperty.Register("Step", typeof(double), typeof(NumericUpDown), new PropertyMetadata(new PropertyChangedCallback(onStepValueChanged)));
        TextValueProperty = DependencyProperty.Register("TextValue", typeof(double), typeof(NumericUpDown), new PropertyMetadata(new PropertyChangedCallback(onTextValueChanged)));
    }

    private static void onStepValueChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        Stp = (double)e.NewValue;
    }
    private static void onMinimumValueChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        Min = (double)e.NewValue;
    }
    private static void onMaximumValueChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        Max = (double)e.NewValue;
    }
    private static void onTextValueChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        Val = (double)e.NewValue;
    }

Then i accessed Max, Min , Stp and Val property in user control's view model to perform my logic.

and XAML code is follows

<local:NumericUpDown x:Name="ctlUpDown" Maximum="28" Minimum="-28" Step="0.25" TextValue="{Binding Path=FramePrice}"></local:NumericUpDown>

and XAML of user control

<StackPanel Margin="5" Orientation="Horizontal" VerticalAlignment="Center">
    <TextBox x:Name="InputTextBox" Grid.Row="0" Grid.Column="0" Grid.RowSpan="1"
             Height="23" VerticalAlignment="Top" 
             Width="50" TextAlignment="Center"  
             KeyDown="InputTextBox_KeyDown" 
             KeyUp="InputTextBox_KeyUp"
             GotFocus="InputTextBox_GotFocus" 
             LostFocus="InputTextBox_LostFocus"  
             MouseWheel="InputTextBox_MouseWheel"
             MouseEnter="InputTextBox_MouseEnter"
             Text="{Binding Path=TextValue, ElementName=ctlUpDown,  Mode=TwoWay,ValidatesOnDataErrors=True,ValidatesOnExceptions=True,NotifyOnValidationError=True}"
             />
</StackPanel>

Answer 1

The first thing I noticed wrong about your code was the properties Maximum, Minimum, Step and TextValue. Here's the TextValue property:

public double TextValue
{
    get
    {
        return (double)GetValue(TextValueProperty);
    }
    set
    {
        SetValue(TextValueProperty, value);
        this.ViewModel.ControlValue = Convert.ToString(value);
    }
}

Properties that are backed by a dependency property, such as the four I mentioned above, should ALWAYS look like the following:

public double TextValue
{
    get { return (double)GetValue(TextValueProperty); }
    set { SetValue(TextValueProperty, value); }
}

In other words, the getter should contain nothing more than a call to GetValue, and the setter should contain nothing more than a call to SetValue.

The reason for this is that when Silverlight changes the value of the TextValue dependency property, it won't do it by using the property above. The values of dependency properties are stored within the Silverlight dependency system, and when Silverlight wants to change the value of one of them, it goes directly to this dependency system. It doesn't call your code at all. Properties like that above are provided only for your convenience, giving you an easy way to access and change the value stored in the dependency property. They will never be called by anything other than your own code.

Generally, if you want a method to be called whenever a dependency property value changes, you need to pass a PropertyChangedCallback in the PropertyMetadata when registering the dependency property. However, I suspect that in your case you won't need to do that.

It seems to me that you have three properties:

• the FramePrice property in your view-model class,
• the TextValue dependency property of your NumericUpDown user control,
• the Text dependency property of the TextBox within your NumericUpDown user control's XAML.

My impression is that you want the FramePrice property in your view-model to always have the same value as the Text property of the TextBox. To do that, you need to bind the FramePrice property to the NumericUpDown's TextValue property, and then bind that to the Text property of the TextBox.

To bind the first two of these properties together, there are a couple of things to change. Firstly, the TextValue property in your <local:NumericUpDown> element should look like

TextValue="{Binding Path=FramePrice}"

The binding {Binding ElementName=FramePrice, Path=DataContext.FramePrice} won't work, because there's no element in your XAML with the attribute x:Name="FramePrice". The value of an ElementName property in a {Binding ...} must match the x:Name of an object in the XAML.

You also need to set up the DataContext for your main page. If your main page view-model object has a zero-argument constructor, one way of doing this is to follow this answer.

To bind the second two properties together, I would:

• add an x:Name attribute to the <UserControl> element of your NumericUpDown control (x:Name="ctlUpDown", say),

• replace the Text property of the TextBox within your NumericUpDown control with the following:

  Text="{Binding Path=TextValue, ElementName=ctlUpDown, Mode=TwoWay, ValidatesOnDataErrors=True, ValidatesOnExceptions=True, NotifyOnValidationError=True}"/>
  

Once you've done that, you can then remove all of the lines this.ViewModel.SomeProperty = ... from your code-behind class. They're not necessary, and as I've already explained they won't be run when you wanted them to.

Finally, is there a reason you're not using the Silverlight Toolkit's NumericUpDown control?

EDIT 2: Against my better judgement I took a look at one of the two Silverlight projects you uploaded (I ignored the one with _2 in it). It bears very little resemblance to your question.

I can only assume you want the two textboxes (one of which is in a user control) to always have the same value. I was able to do this after making the following changes:

• MainPageViewModel.cs: add ClearErrorFromProperty("DPropertyBind"); to the property setter. (Otherwise the validation error never gets cleared.)

• MyUserControlWVM.xaml: removed reference to LostFocus event handler, added binding on Text property and added add x:Name attribute to the <UserControl> element. In other words, it now looks like the following:

  <UserControl x:Class="DependencyPropertyBinding.MyUserControlWVM"
      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"
      x:Name="ctlWVM"
      d:DesignHeight="300" d:DesignWidth="205">
      <StackPanel Orientation="Horizontal" Width="204" Height="32">
          <TextBox x:Name="textbox" Height="30" Width="200" Text="{Binding Path=DProperty, ElementName=ctlWVM, Mode=TwoWay, NotifyOnValidationError=True, ValidatesOnDataErrors=True, ValidatesOnExceptions=True}" />
      </StackPanel>
  </UserControl>
  

• MyUserControlWVM.xaml.cs: renamed dependency property DependencyPropertyValue to DPropertyProperty (the naming convention is that the static readonly field has the name of the property (in this case DProperty) with Property appended). I also removed the TextBox_LostFocus event handler.

Answer 2

If the code above is accurate you have spelt FramePrice as FranePrice in the binding

The output window should have shown this as a binding error when the page loaded.

it is currently Binding ElementName=FranePrice, Path=DataContext.FranePrice

should be: Binding ElementName=FramePrice, Path=DataContext.FramePrice

"With great binding capabilities comes great responsibility" :)