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POHow can I conditionally style only the text in the selected item of a ComboBox?
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  1. POHow can I conditionally style only the text in the selected item of a ComboBox?
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    copied!<p>I have a situation where I need to style the selected item in a ComboBox differently (make the text bold) when it is one of all except one value. For example, in the drop-down box labelled "What is your favourite primary colour?" I would have four options: <code>No Preference</code>, <code>Red</code>, <code>Green</code>, and <code>Blue</code>. The ComboBox items are just text with default styling, no images or anything else fancy, and are C# classes, not wrapped in ComboBoxItems. </p> <p>When the user specifies a preference from the list, I want to highlight that choice by setting the text of the selected item <em>in the collapsed list</em> to be bold. If the user chooses <code>No Preference</code>, the font weight should remain normal. </p> <p>I have achieved a 90% solution by setting the FontWeight property on the ComboBox to Bold in a Style with a DataTrigger defined as <code>SelectedItem != No Preference</code>. However, this styles all items in the ComboBox's list of items, including all those in the drop-down list. I would like those items to <em>always</em> be displayed with a normal font weight. </p> <p>Is this possible?</p> <p><strong>Edit</strong></p> <p>I have been trying @crazyarabian's method of styling the ComboBoxItem with a MultiTrigger. The style definition is:</p> <pre><code>&lt;Style x:Key="SelectedItemStyle"&gt; &lt;Setter Property="ComboBoxItem.FontWeight" Value="Normal" /&gt; &lt;Style.Triggers&gt; &lt;MultiTrigger&gt; &lt;MultiTrigger.Conditions&gt; &lt;Condition Property="ComboBoxItem.IsSelected" Value="True" /&gt; &lt;Condition Binding="{Binding IsNoPreferenceSelected,Mode=OneWay}" Value="False" /&gt; &lt;/MultiTrigger.Conditions&gt; &lt;Setter Property="ComboBoxItem.FontWeight" Value="Bold" /&gt; &lt;/MultiTrigger&gt; &lt;/Style.Triggers&gt; &lt;/Style&gt; </code></pre> <p>and it is applied to a ComboBox in the following DataTemplate:</p> <pre><code>&lt;DataTemplate x:Key="PrimaryColoursTemplate" DataType="{x:Type ViewModels:PrimaryColoursViewModel}"&gt; &lt;ComboBox ItemsSource="{Binding PrimaryColours}" SelectedItem="{Binding SelectedPrimaryColour}" ItemContainerStyle="{StaticResource SelectedItemStyle}" /&gt; &lt;/DataTemplate&gt; </code></pre> <p>Unfortunately, this kills WPF: </p> <pre><code>System.Windows.Data Error: 8 : Cannot save value from target back to source. BindingExpression:Path=IsDropDownOpen; DataItem='ComboBox' (Name=''); target element is 'ToggleButton' (Name=''); target property is 'IsChecked' (type 'Nullable`1') InvalidOperationException:'System.InvalidOperationException: Must have non-null value for 'Property'. </code></pre> <p>The application dies with a <code>NullReferenceException</code>, which is thrown after the InvalidOperationException above (or perhaps leads to it, I can't decipher the output). The only thing I can think of that might be causing this is resolving the property in the binding in my second MultiTrigger condition, but I don't get any binding errors at all. Here's the top of the stack trace in case that helps too:</p> <pre><code>InvalidOperationException:'System.InvalidOperationException: Must have non-null value for 'Property'. at System.Windows.Condition.Seal(ValueLookupType type) at System.Windows.ConditionCollection.Seal(ValueLookupType type) at System.Windows.MultiTrigger.Seal() at System.Windows.TriggerCollection.Seal() at System.Windows.Style.Seal() at System.Windows.StyleHelper.UpdateStyleCache(FrameworkElement fe, FrameworkContentElement fce, Style oldStyle, Style newStyle, Style&amp; styleCache) at System.Windows.FrameworkElement.OnStyleChanged(DependencyObject d, DependencyPropertyChangedEventArgs e) at System.Windows.DependencyObject.OnPropertyChanged(DependencyPropertyChangedEventArgs e) at System.Windows.FrameworkElement.OnPropertyChanged(DependencyPropertyChangedEventArgs e) at System.Windows.DependencyObject.NotifyPropertyChange(DependencyPropertyChangedEventArgs args) at System.Windows.DependencyObject.UpdateEffectiveValue(EntryIndex entryIndex, DependencyProperty dp, PropertyMetadata metadata, EffectiveValueEntry oldEntry, EffectiveValueEntry&amp; newEntry, Boolean coerceWithDeferredReference, Boolean coerceWithCurrentValue, OperationType operationType) at System.Windows.DependencyObject.SetValueCommon(DependencyProperty dp, Object value, PropertyMetadata metadata, Boolean coerceWithDeferredReference, Boolean coerceWithCurrentValue, OperationType operationType, Boolean isInternal) at System.Windows.DependencyObject.SetValue(DependencyProperty dp, Object value) at System.Windows.Controls.ItemsControl.ApplyItemContainerStyle(DependencyObject container, Object item) </code></pre>
 

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