Databinding one property on a Dialog from two contols

Question

I have a Window that I'm showing using ShowDialog. One of the values I'm trying to get from the user is size in GB or TB. So I have two controls for this, an IntegerUpDown from the WPF Extended Toolkit and a ComboBox:

<xctk:IntegerUpDown Name="SizeN" Minimum="1" Maximum="1023" Increment="1" Value="100"/>
<ComboBox Name="SizeS" SelectedIndex="0">
    <ComboBoxItem>GB</ComboBoxItem>
    <ComboBoxItem>TB</ComboBoxItem>
</ComboBox>

I am setting the Dialog's DataContext to itself. I have defined the Capacity property:

public ulong Capacity { get; set; }

public CustomWindow()
{
    InitializeComponent();
    DataContext = this;
}

I have already created an IMultiValueConverter, PowerConverter, that takes an int and a string and returns ulong. I think the correct MultiBinding is:

<Window.Resources>
    <local:PowerConverter x:Key="CapacityConverter" />
</Window.Resources>

<MultiBinding Converter="{StaticResource CapacityConverter}">
    <Binding ElementName="SizeN" Path="Value" />
    <Binding ElementName="SizeS" Path="SelectedValue" />
</MultiBinding>

I can't figure out how to assign this binding to the Capacity property on the Dialog. I want WPF to automagically set the Capacity property for me. Any ideas?

Answer 1

I had to convert Capacity into a DependencyProperty on CustomWindow, set the SelectedValuePath attribute on the ComboBox, and assign the binding to Capacity in the style.

XAML:

<Window xmlns:="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:xctk="clr-namespace:Xceed.Wpf.Toolkit;assembly=WPFToolkit.Extended"
        xmlns:local="clr-namespace:MyProject"
        x:Class="MyProject.CustomWindow" Title="CustomWindow"
        DataContext="{Binding RelativeSource={RelativeSource Self}}">
    <Window.Resources>
        <local:PowerConverter x:Key="CapacityConverter" />
    </Window.Resources>
    <Window.Style>
        <Style TargetType="{x:Type local:CustomWindow}">
            <Setter Property="Capacity">
                <Setter.Value>
                    <MultiBinding Converter="{StaticResource CapacityConverter}"
                                  Mode="TwoWay">
                        <Binding  ElementName="SizeNumber" Path="Value"
                                  Mode="TwoWay" />
                        <Binding  ElementName="SizeSuffix" Path="SelectedValue"
                                  Mode="TwoWay" />
                    </MultiBinding>
                </Setter.Value>
            </Setter>
        </Style>
    </Window.Style>
    <StackPanel>
        <xctk:IntegerUpDown Name="SizeNumber" Minimum="1" Maximum="1023" Increment="1"
                            Value="100"/>                        
        <ComboBox Name="SizeSuffix" SelectedIndex="0" SelectedValuePath="Content">
            <ComboBoxItem>GB</ComboBoxItem>                        
            <ComboBoxItem>TB</ComboBoxItem>                        
        </ComboBox>
    </StackPanel>
</Window>

Code behind:

public partial class CustomWindow : Window
{
    public CustomWindow()
    {
        InitializeComponent();
    }

    public static readonly DependencyProperty CapacityProperty =
        DependencyProperty.Register("Capacity", typeof(ulong), typeof(CustomWindow));

    public ulong Capacity
    {
        get
        {
            return (ulong)GetValue(CapacityProperty);
        }
        set
        {
            SetValue(CapacityProperty, value);
        }
    }
}