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POHow can you get a XAML TextBlock to collapse when it contains no data?
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  1. POHow can you get a XAML TextBlock to collapse when it contains no data?
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    copied!<p>I want to tell WPF: "<strong>If TextBlock contains no data, then don't show it.</strong>"</p> <p><strong>TRY #1</strong> with a <strong>simple trigger</strong> produces the error "<em>'Text' member is not valid because it does not have a qualifying type name.</em>":</p> <pre><code>&lt;StackPanel Margin="10"&gt; &lt;TextBlock Padding="10" Background="Yellow" Text="{Binding MainMessage}"&gt; &lt;TextBlock.Triggers&gt; &lt;Trigger Property="Text" Value="{x:Null}"&gt; &lt;Setter Property="Visibility" Value="Collapsed"/&gt; &lt;/Trigger&gt; &lt;/TextBlock.Triggers&gt; &lt;/TextBlock&gt; &lt;/StackPanel&gt; </code></pre> <p><strong>TRY #2</strong> with a <strong>style trigger</strong> produces the error <em>The type 'style' does not contain a public type-converter class</em>:</p> <pre><code>&lt;UserControl x:Class="TestItemsSource234.Views.SmartForm" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"&gt; &lt;UserControl.Resources&gt; &lt;Style x:Key="MainMessageStyle" TargetType="TextBlock"&gt; &lt;Style.Triggers&gt; &lt;Trigger&gt; &lt;Trigger Property="Text" Value="{x:Null}"&gt; &lt;Setter Property="Visibility" Value="Collapsed"/&gt; &lt;/Trigger&gt; &lt;/Trigger&gt; &lt;/Style.Triggers&gt; &lt;/Style&gt; &lt;/UserControl.Resources&gt; &lt;StackPanel Margin="10"&gt; &lt;TextBlock Style="MainMessageStyle" Padding="10" Background="Yellow" Text="{Binding MainMessage}"/&gt; &lt;/StackPanel&gt; &lt;/UserControl&gt; </code></pre> <p><strong>TRY #3</strong> with a <strong>style DataTrigger</strong> produces the same error <em>The type 'style' does not contain a public type-converter class</em>:</p> <pre><code>&lt;UserControl x:Class="TestItemsSource234.Views.SmartForm" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"&gt; &lt;UserControl.Resources&gt; &lt;Style x:Key="MainMessageStyle" TargetType="TextBlock"&gt; &lt;Style.Triggers&gt; &lt;Trigger&gt; &lt;DataTrigger Binding="{Binding MainMessage}" Value="{x:Null}"&gt; &lt;Setter Property="Visibility" Value="Collapsed"/&gt; &lt;/DataTrigger&gt; &lt;/Trigger&gt; &lt;/Style.Triggers&gt; &lt;/Style&gt; &lt;/UserControl.Resources&gt; &lt;StackPanel Margin="10"&gt; &lt;TextBlock Style="MainMessageStyle" Padding="10" Background="Yellow" Text="{Binding MainMessage}"/&gt; &lt;/StackPanel&gt; &lt;/UserControl&gt; </code></pre> <p><strong>TRY #4</strong>: OK, that was a dumb oversight of mine, forgot the <strong>StaticResource</strong>, but even then both Try #2 and Try #3 get a new error <em>The type System.Windows.Trigger in Style is unknown</em>:</p> <pre><code>&lt;UserControl x:Class="TestItemsSource234.Views.SmartForm" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"&gt; &lt;UserControl.Resources&gt; &lt;Style x:Key="MainMessageStyle" TargetType="TextBlock"&gt; &lt;Style.Triggers&gt; &lt;Trigger&gt; &lt;Trigger Property="Text" Value=""&gt; &lt;Setter Property="Visibility" Value="Collapsed"/&gt; &lt;/Trigger&gt; &lt;/Trigger&gt; &lt;/Style.Triggers&gt; &lt;/Style&gt; &lt;/UserControl.Resources&gt; &lt;StackPanel Margin="10"&gt; &lt;TextBlock Style="{StaticResource MainMessageStyle}" Padding="10" Background="Yellow" Text="{Binding MainMessage}"/&gt; &lt;/StackPanel&gt; &lt;/UserControl&gt; </code></pre> <p><strong>So how do I do this?</strong></p> <h1>ANSWER:</h1> <p>OK, so that was a maddening syntax hunt with a happy end, here's the version that works, hope it helps somebody, lessons learned:</p> <ul> <li>if trigger, then <strong>style</strong></li> <li>if style, then <strong>StaticResource</strong></li> <li>if binding, then <strong>DataTrigger</strong></li> </ul> <p>code that works:</p> <pre><code>&lt;UserControl x:Class="TestItemsSource234.Views.SmartForm" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"&gt; &lt;UserControl.Resources&gt; &lt;Style x:Key="MainMessageStyle" TargetType="TextBlock"&gt; &lt;Style.Triggers&gt; &lt;DataTrigger Binding="{Binding MainMessage}" Value="{x:Null}"&gt; &lt;Setter Property="Visibility" Value="Collapsed"/&gt; &lt;/DataTrigger&gt; &lt;/Style.Triggers&gt; &lt;/Style&gt; &lt;/UserControl.Resources&gt; &lt;StackPanel Margin="10"&gt; &lt;ItemsControl ItemsSource="{Binding DataTypeViews}"/&gt; &lt;TextBlock Style="{StaticResource MainMessageStyle}" Padding="10" Background="Yellow" Text="{Binding MainMessage}"/&gt; &lt;/StackPanel&gt; &lt;/UserControl&gt; </code></pre>
 

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