Navigation Keys
The Pocket PC has six navigation controls that allow a user to start applications, navigate lists, open records, and close fields and dialog boxes. The following table shows the default navigation controls.
| Navigation control | Description |
|---|---|
| Action key | Acts as the ENTER key |
| Program keys | Start applications |
| Up control | Acts as an UP ARROW key |
| Down control | Acts as a DOWN ARROW key |
| Left control | Acts as a LEFT ARROW key |
| Right control | Acts as a RIGHT ARROW key |
Although every Pocket PC implements these controls, the OEM decides on the number of controls and their placement. For example, it is possible to combine the direction keys and the Action key into a wheel that is similar in form to the wheel on the Microsoft IntelliMouse®. Pressing the wheel sends the VK_ENTER message, and spinning the wheel sends the VK_UP and VK_DOWN messages.
In most respects, programming a navigation control for a Windows Mobile-based device is identical to programming any other Windows–based input device; that is, your application captures messages and acts on them in the WndProc function. An OEM provides the driver that links each navigation control with WM_KEYUP and WM_KEYDOWN messages individually or in a series. Each message has a virtual key message in its wParam parameter. The driver starts when the user presses a navigation control. The driver then sends the window messages to the device shell, which in turn passes the messages to the current application. See Message Map for Navigation Controls for a detailed itemization of a possible operation/message sequence.
The OEM also determines the original purpose of each program key. When pressed, a program key usually starts a predetermined application. However, there are some opportunities for application developers to modify or extend the behavior of certain program keys. For more detailed information, see Program Keys.
Windows Mobile-based Smartphones have a Back key that provides, depending on the current user interface, the default functions described in the following table.
| User interface | Back key functions |
|---|---|
| Window | Default to display the previous screen. |
| Message box or a dialog box without edit controls | Default to close the message box or dialog box. |
| Dialog box with edit controls | Override default to delete characters to the left of the cursor in an edit control. |
For a dialog box with edit controls, it is recommended that you override the default behavior of the Back key and send it to the control with focus. This enables the user to modify data within the control, replicating the functionality of the Backspace key on a desktop keyboard.
Note If a window is programmed to override the Back key, you can use the SHNavigateBack function to display the previous screen.
To override the Back key, you send the SHCMBM_OVERRIDEKEY message to the menu bar specified in the SHMENUBARINFO structure during the handling of the Windows CE WM_INITDIALOG message. For an example of this operation, see How to: Override the Back Key for Dialog Boxes with Edit Controls.
See Also
How to: Handle the Back Key for Dialog Boxes Without Edit Controls | How to: Override the Back Key for Dialog Boxes with Edit Controls | Mobile Device Hardware Overview | Program Keys | Message Map for Navigation Controls
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