Common dialog boxes provide context-sensitive Help for the standard controls of the dialog box. To provide additional help for a common dialog box, you can display a Help button and process messages generated when the user clicks the button. The Help button is a supplement to the default context-sensitive Help. The Help button is useful for describing the general purpose of the dialog box as it applies to your application.
All common dialog boxes provide context-sensitive Help for the standard controls of the dialog box. The user can display Help for individual controls by any of the following methods:
If you customize a dialog box by adding new controls, you must also extend help support for these controls by processing requests for help in the hook procedure. The hook procedure receives the following messages when the user requests help.
| User Action | Message |
|---|---|
| The user clicked the right mouse button over a control. | WM_CONTEXTMENU |
| The user pressed the f1 key. | WM_HELP |
| The user clicked the ? button on the title bar and then clicked a control. | WM_HELP |
You should process these messages for the controls you have added, but let the default dialog box procedure process the messages for the standard controls. For more information about how to process these messages, see the Help overview.
You can display a Help button in any of the common dialog boxes by setting a SHOWHELP value in the Flags member of the initialization structure for the dialog box. If you display the Help button, you must process the user's request for help. The processing can be done either in one of your application's window procedures or in a hook procedure for the dialog box. Typically, you would process the request for help by calling the WinHelp function.
To process help messages in one of your window procedures, you must get a message identifier for the string defined by the HELPMSGSTRING value and identify the window to receive messages. To get the message identifier, specify HELPMSGSTRING as the parameter in a call to the RegisterWindowMessage function. When you create the common dialog box, use the hwndOwner member of the dialog box initialization structure to identify the window that is to receive the messages. The dialog box procedure sends the message to the window procedure whenever the user clicks the Help button.
To process help messages in a hook procedure, you should process the WM_COMMAND message. The hook procedure provides help if the wParam parameter of this message indicates that the user clicked the Help button. The identifier of the Help button is the pshHelp constant defined in the DLGS.H file.
Hook procedures for the Explorer-style Open and Save As common dialog boxes do not receive WM_COMMAND messages for the Help button. Instead, the dialog box sends a CDN_HELP notification message to the hook procedure when the Help button is clicked.