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39 lines
4.0 KiB
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39 lines
4.0 KiB
Markdown
---
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title: "How to: Enable a Command"
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ms.date: "03/30/2017"
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dev_langs:
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- "csharp"
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- "vb"
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helpviewer_keywords:
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- "CommandBindings [WPF]"
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- "commanding [WPF]"
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ms.assetid: d8016266-58d9-48f7-8298-a86b7ed49fbd
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---
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# How to: Enable a Command
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The following example demonstrates how to use commanding in Windows Presentation Foundation (WPF). The example shows how to associate a <xref:System.Windows.Input.RoutedCommand> to a <xref:System.Windows.Controls.Button>, create a <xref:System.Windows.Input.CommandBinding>, and create the event handlers which implement the <xref:System.Windows.Input.RoutedCommand>. For more information on commanding, see the [Commanding Overview](commanding-overview.md).
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## Example
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The first section of code creates the user interface (UI), which consists of a <xref:System.Windows.Controls.Button> and a <xref:System.Windows.Controls.StackPanel>, and creates a <xref:System.Windows.Input.CommandBinding> that associates the command handlers with the <xref:System.Windows.Input.RoutedCommand>.
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The <xref:System.Windows.Input.ICommandSource.Command%2A> property of the <xref:System.Windows.Controls.Button> is associated with the <xref:System.Windows.Input.ApplicationCommands.Close%2A> command.
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The <xref:System.Windows.Input.CommandBinding> is added to the <xref:System.Windows.Input.CommandBindingCollection> of the root <xref:System.Windows.Window>. The <xref:System.Windows.Input.CommandBinding.Executed> and <xref:System.Windows.Input.CommandBinding.CanExecute> event handlers are attached to this binding and associated with the <xref:System.Windows.Input.ApplicationCommands.Close%2A> command.
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Without the <xref:System.Windows.Input.CommandBinding> there is no command logic, only a mechanism to invoke the command. When the <xref:System.Windows.Controls.Button> is clicked, the <xref:System.Windows.Input.CommandManager.PreviewExecuted> <xref:System.Windows.RoutedEvent> is raised on the command target followed by the <xref:System.Windows.Input.CommandManager.Executed> <xref:System.Windows.RoutedEvent>. These events traverse the element tree looking for a <xref:System.Windows.Input.CommandBinding> for that particular command. It is worth noting that because <xref:System.Windows.RoutedEvent> tunnel and bubble through the element tree, care must be taken in where the <xref:System.Windows.Input.CommandBinding> is put. If the <xref:System.Windows.Input.CommandBinding> is on a sibling of the command target or another node that is not on the route of the <xref:System.Windows.RoutedEvent>, the <xref:System.Windows.Input.CommandBinding> will not be accessed.
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[!code-xaml[EnableCloseCommand#CloseCommandBinding](~/samples/snippets/csharp/VS_Snippets_Wpf/EnableCloseCommand/CSharp/Window1.xaml#closecommandbinding)]
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[!code-csharp[EnableCloseCommand#CloseCommandBindingCodeBehind](~/samples/snippets/csharp/VS_Snippets_Wpf/EnableCloseCommand/CSharp/Window1.xaml.cs#closecommandbindingcodebehind)]
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[!code-vb[EnableCloseCommand#CloseCommandBindingCodeBehind](~/samples/snippets/visualbasic/VS_Snippets_Wpf/EnableCloseCommand/VisualBasic/Window1.xaml.vb#closecommandbindingcodebehind)]
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The next section of code implements the <xref:System.Windows.Input.CommandManager.Executed> and <xref:System.Windows.Input.CommandBinding.CanExecute> event handlers.
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The <xref:System.Windows.Input.CommandManager.Executed> handler calls a method to close the open file. The <xref:System.Windows.Input.CommandBinding.CanExecute> handler calls a method to determine whether a file is open. If a file is open, <xref:System.Windows.Input.CanExecuteRoutedEventArgs.CanExecute%2A> is set to `true`; otherwise, it is set to `false`.
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[!code-csharp[EnableCloseCommand#CloseCommandHandler](~/samples/snippets/csharp/VS_Snippets_Wpf/EnableCloseCommand/CSharp/Window1.xaml.cs#closecommandhandler)]
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[!code-vb[EnableCloseCommand#CloseCommandHandler](~/samples/snippets/visualbasic/VS_Snippets_Wpf/EnableCloseCommand/VisualBasic/Window1.xaml.vb#closecommandhandler)]
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## See also
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- [Commanding Overview](commanding-overview.md)
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