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POWhat is the advantage of setting DataContext in code instead of XAML?
 

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  1. POWhat is the advantage of setting DataContext in code instead of XAML?
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    <p>There seem to be two main ways to define DataContext in WPF:</p> <ul> <li>either <strong>in code</strong> like this:</li> </ul> <p>App.xaml.cs (taken from the <a href="http://www.codeplex.com/wpf/Release/ProjectReleases.aspx?ReleaseId=14962" rel="noreferrer">WPF MVVM Toolkit template</a>):</p> <pre><code>public partial class App : Application { private void OnStartup(object sender, StartupEventArgs e) { // Create the ViewModel and expose it using the View's DataContext MainView mainView = new MainView(); MainViewModel mainViewModel = new MainViewModel(); mainViewModel.LoadCustomers("c:\\testdata2\\Customers.xml"); mainView.DataContext = mainViewModel; mainView.Show(); } } </code></pre> <ul> <li>or <strong>in XAML</strong> like this:</li> </ul> <p>Window1.xaml:</p> <pre><code>&lt;DockPanel&gt; &lt;StackPanel HorizontalAlignment="Left" DockPanel.Dock="Top" Orientation="Horizontal"&gt; &lt;StackPanel.DataContext&gt; &lt;local:CustomerViewModel /&gt; &lt;/StackPanel.DataContext&gt; &lt;TextBlock Text="{Binding Path=FirstName}" /&gt; &lt;TextBlock Text=" " /&gt; &lt;TextBlock Text="{Binding Path=LastName}" /&gt; &lt;/StackPanel&gt; &lt;StackPanel HorizontalAlignment="Left" VerticalAlignment="top" DockPanel.Dock="Top" Orientation="Horizontal"&gt; &lt;ListBox ItemsSource="{Binding Source={StaticResource FileNames}}" /&gt; &lt;/StackPanel&gt; &lt;StackPanel HorizontalAlignment="Left" VerticalAlignment="top" DockPanel.Dock="Top" Orientation="Horizontal"&gt; &lt;ComboBox ItemsSource="{Binding Source={StaticResource Directories}}" SelectedIndex="0" /&gt; &lt;/StackPanel&gt; &lt;StackPanel HorizontalAlignment="Left" VerticalAlignment="top" DockPanel.Dock="Top" Orientation="Horizontal"&gt; &lt;StackPanel.DataContext&gt; &lt;local:SystemInformationViewModel /&gt; &lt;/StackPanel.DataContext&gt; &lt;TextBlock Text="{Binding Path=CurrentTime}" /&gt; &lt;/StackPanel&gt; &lt;/DockPanel&gt; </code></pre> <p>One advantage that defining the DataContext in XAML has is that <strong>your data shows up in Expression Blend design mode</strong> and Expression Blend allows you to do quite a lot within the GUI e.g. choose fields from your datasource, etc. <a href="http://tanguay.info/web/index.php?pg=codeExamples&amp;id=176" rel="noreferrer">as shown here</a>.</p> <p>I have read that binding <strong>ADO.NET objects cannot be bound in XAML</strong> (although I don't see why you could write a minimal wrapper for them to which you could bind from XAML).</p> <p>Strange that the <strong>WPF Team in making the WPF MVVM templates define the DataContext in code</strong> which very quickly makes it impracticable to edit your Views in Expression Blend, since your data doesn't show up in design mode which is often a significant part of the layout.</p> <p>So I'm thinking there <strong>must be some advantage</strong> down the road to setting the DataContext in code instead of XAML, anyone know what it is?</p>
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