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POWhy is the multibinding always passing DependencyProperty.UnsetValue for the first value?
 

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  1. POWhy is the multibinding always passing DependencyProperty.UnsetValue for the first value?
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    <p>In a form in my WPF application, I am building a psuedo bar graph. The bar graph consists of a Grid with 12 columns. Each column contains a Rectangle. I am using databinding to bind the height of the rectangle to the data that I want to graph. The xaml looks like this:</p> <pre><code>&lt;Border BorderBrush="{DynamicResource ControlBorder}" BorderThickness="2" Grid.Column="1" Grid.Row="0" Margin="0,5" Name="SNRGraphBorder"&gt; &lt;Grid&gt; &lt;Grid.ColumnDefinitions&gt; &lt;ColumnDefinition Width="*" /&gt; &lt;ColumnDefinition Width="*" /&gt; &lt;ColumnDefinition Width="*" /&gt; &lt;ColumnDefinition Width="*" /&gt; &lt;ColumnDefinition Width="*" /&gt; &lt;ColumnDefinition Width="*" /&gt; &lt;ColumnDefinition Width="*" /&gt; &lt;ColumnDefinition Width="*" /&gt; &lt;ColumnDefinition Width="*" /&gt; &lt;ColumnDefinition Width="*" /&gt; &lt;ColumnDefinition Width="*" /&gt; &lt;ColumnDefinition Width="*" /&gt; &lt;/Grid.ColumnDefinitions&gt; &lt;Rectangle Fill="{DynamicResource TextForeground}" Grid.Column="0" Margin="1,5,2,0" Name="Data01" VerticalAlignment="Bottom"&gt; &lt;Rectangle.Height&gt; &lt;MultiBinding Converter="{StaticResource ScaleData}"&gt; &lt;Binding Source="{StaticResource XmlProvider}" XPath="a:PathToData}" /&gt; &lt;Binding Path="RectangleHeight" RelativeSource="{RelativeSource AncestorType={x:Type cs:MyControl}}" /&gt; &lt;/MultiBinding&gt; &lt;/Rectangle.Height&gt; &lt;/Rectangle&gt; . . . &lt;/Grid&gt; &lt;/Border&gt; </code></pre> <p>I've only included one rectangle for brevity.</p> <p>Here's the code for the IMultiValueConverter used in the MultiBinding:</p> <pre><code>public class ScaleDataConverter : IMultiValueConverter { public object Convert( object[] values, Type targetType, object parameter, System.Globalization.CultureInfo culture ) { double snr = 0.0; if ( values[ 0 ] is string ) { snr = double.Parse( values[ 0 ] as string ); } else if ( values[ 0 ] is int || values[ 0 ] is double || values[ 0 ] is long || values[ 0 ] is float ) { snr = (double) values[ 0 ]; } else { return values[ 0 ]; } double ActualHeight = (double) values[ 1 ]; return snr * ActualHeight / 99.0; } public object[] ConvertBack( object value, Type[] targetTypes, object parameter, System.Globalization.CultureInfo culture ) { throw new NotImplementedException(); } } </code></pre> <p>Finally, here's the code behind for this control:</p> <pre><code>public partial class MyControl : UserControl { public XmlDataProvider DataProvider { get; set; } public DeviceMonitor DeviceMonitor { get; set; } public double RectangleHeight { get { return SNRGraphBorder.ActualHeight; } } public MyControl() { InitializeComponent(); DataProvider = Resources[ "XmlProvider" ] as XmlDataProvider; } private void GetDiagnosticsInfo() { if ( DeviceMonitor != null ) { XmlDocument diagnosticsDoc = new XmlDocument(); string info = DeviceMonitor.GetDiagnosticInfo(); diagnosticsDoc.LoadXml( info ); DataProvider.Document = diagnosticsDoc; } } private void RefreshButton_Click( object sender, RoutedEventArgs e ) { GetDiagnosticsInfo(); e.Handled = true; } } </code></pre> <p>I've put breakpoints into the converter on the <code>if ( values[ 0 ] is string )</code> line. I see that the first entry in the values array is always DependencyProperty.UnsetValue. Yet I know that the XML has other data for this property. What am I doing wrong?</p> <p>Thanks</p> <p>Tony</p>
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    1. USTony Vitabile
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    1. CODid you add XmlDataProvider with key "XmlProvider" to Resources? And are you sure that "a:PathToData}" is correct? is one bracket?
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      1. POWhy is the multibinding always passing DependencyProperty.UnsetValue for the first value?
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    2. COYes, I did add XmlDataProvider with key "XmlProvider" to Resources. I just didn't show it in the example. My XPaths are correct: I had an earlier version of the code without the IMultiBinding and IMultConverter and I was able to see the data i nthat version. The problem is that in every call to the IMultiConverter, the first parameter is always DependencyProperty.UnsetValue.
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      1. POWhy is the multibinding always passing DependencyProperty.UnsetValue for the first value?
      1. USTony Vitabile
    3. COhm.. interesting.. and 'RectangleHeight' has correct value in 'IMultiValueConverter'?
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      1. POWhy is the multibinding always passing DependencyProperty.UnsetValue for the first value?
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