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67 lines
5.4 KiB
Markdown
67 lines
5.4 KiB
Markdown
---
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title: "How to: Modify Keyboard Input to a Standard Control"
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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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- "keyboard input [Windows Forms], modifying"
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- "modifying keyboard input"
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- "Windows Forms, modifying keyboard input"
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- "keyboards [Windows Forms], keyboard input"
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ms.assetid: 626d3712-d866-4988-bcda-a2d5b36ec0ba
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---
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# How to: Modify Keyboard Input to a Standard Control
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Windows Forms provides the ability to consume and modify keyboard input. Consuming a key refers to handling a key within a method or event handler so that other methods and events further down the message queue do not receive the key value. Modifying a key refers to modifying the value of a key so that methods and event handlers further down the message queue receive a different key value. This topic shows how to accomplish these tasks.
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### To consume a key
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- In a <xref:System.Windows.Forms.Control.KeyPress> event handler, set the <xref:System.Windows.Forms.KeyPressEventArgs.Handled%2A> property of the <xref:System.Windows.Forms.KeyPressEventArgs> class to `true`.
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-or-
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In a <xref:System.Windows.Forms.Control.KeyDown> event handler, set the <xref:System.Windows.Forms.KeyEventArgs.Handled%2A> property of the <xref:System.Windows.Forms.KeyEventArgs> class to `true`.
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> [!NOTE]
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> Setting the <xref:System.Windows.Forms.KeyEventArgs.Handled%2A> property in the <xref:System.Windows.Forms.Control.KeyDown> event handler does not prevent the <xref:System.Windows.Forms.Control.KeyPress> and <xref:System.Windows.Forms.Control.KeyUp> events from being raised for the current keystroke. Use the <xref:System.Windows.Forms.KeyEventArgs.SuppressKeyPress%2A> property for this purpose.
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The following example is an excerpt from a `switch` statement that examines the <xref:System.Windows.Forms.KeyPressEventArgs.KeyChar%2A> property of the <xref:System.Windows.Forms.KeyPressEventArgs> received by a <xref:System.Windows.Forms.Control.KeyPress> event handler. This code consumes the 'A' and 'a' character keys.
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[!code-csharp[System.Windows.Forms.KeyBoardInput#6](~/samples/snippets/csharp/VS_Snippets_Winforms/System.Windows.Forms.KeyboardInput/CS/form1.cs#6)]
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[!code-vb[System.Windows.Forms.KeyBoardInput#6](~/samples/snippets/visualbasic/VS_Snippets_Winforms/System.Windows.Forms.KeyboardInput/VB/form1.vb#6)]
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### To modify a standard character key
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- In a <xref:System.Windows.Forms.Control.KeyPress> event handler, set the <xref:System.Windows.Forms.KeyPressEventArgs.KeyChar%2A> property of the <xref:System.Windows.Forms.KeyPressEventArgs> class to the value of the new character key.
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The following example is an excerpt from a `switch` statement that modifies 'B' to 'A' and 'b' to 'a'. Note that the <xref:System.Windows.Forms.KeyPressEventArgs.Handled%2A> property of the <xref:System.Windows.Forms.KeyPressEventArgs> parameter is set to `false`, so that the new key value is propagated to other methods and events in the message queue.
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[!code-csharp[System.Windows.Forms.KeyBoardInput#7](~/samples/snippets/csharp/VS_Snippets_Winforms/System.Windows.Forms.KeyboardInput/CS/form1.cs#7)]
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[!code-vb[System.Windows.Forms.KeyBoardInput#7](~/samples/snippets/visualbasic/VS_Snippets_Winforms/System.Windows.Forms.KeyboardInput/VB/form1.vb#7)]
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### To modify a noncharacter key
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- Override a <xref:System.Windows.Forms.Control> method that processes Windows messages, detect the WM_KEYDOWN or WM_SYSKEYDOWN message, and set the <xref:System.Windows.Forms.Message.WParam%2A> property of the <xref:System.Windows.Forms.Message> parameter to the <xref:System.Windows.Forms.Keys> value that represents the new noncharacter key.
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The following code example demonstrates how to override the <xref:System.Windows.Forms.Control.PreProcessMessage%2A> method of a control to detect keys F1 through F9 and modify any F3 key press to F1. For more information on <xref:System.Windows.Forms.Control> methods that you can override to intercept keyboard messages, see [User Input in a Windows Forms Application](user-input-in-a-windows-forms-application.md) and [How Keyboard Input Works](how-keyboard-input-works.md).
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[!code-csharp[System.Windows.Forms.KeyBoardInput#12](~/samples/snippets/csharp/VS_Snippets_Winforms/System.Windows.Forms.KeyboardInput/CS/form1.cs#12)]
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[!code-vb[System.Windows.Forms.KeyBoardInput#12](~/samples/snippets/visualbasic/VS_Snippets_Winforms/System.Windows.Forms.KeyboardInput/VB/form1.vb#12)]
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## Example
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The following code example is the complete application for the code examples in the previous sections. The application uses a custom control derived from the <xref:System.Windows.Forms.TextBox> class to consume and modify keyboard input.
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[!code-csharp[System.Windows.Forms.KeyBoardInput#0](~/samples/snippets/csharp/VS_Snippets_Winforms/System.Windows.Forms.KeyboardInput/CS/form1.cs#0)]
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[!code-vb[System.Windows.Forms.KeyBoardInput#0](~/samples/snippets/visualbasic/VS_Snippets_Winforms/System.Windows.Forms.KeyboardInput/VB/form1.vb#0)]
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## Compiling the Code
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This example requires:
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- References to the System, System.Drawing and System.Windows.Forms assemblies.
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## See also
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- [Keyboard Input in a Windows Forms Application](keyboard-input-in-a-windows-forms-application.md)
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- [User Input in a Windows Forms Application](user-input-in-a-windows-forms-application.md)
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- [How Keyboard Input Works](how-keyboard-input-works.md)
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