The WM_INITDIALOG Message
Windows does
not send a
WM_CREATE message to the dialog box procedure. Instead, it sends a
WM_INITDIALOG message when it creates the dialog box and all its controls but before it
displays the dialog box. The procedure should carry out any initialization
required to ensure that the dialog box displays the current settings associated with
the command or task. For example, when a dialog box contains a control to show
the current drive and directory, the procedure must determine the current drive
and directory and set the control to that value.
The procedure can initialize controls by using functions such as
SetDlgItemText and
CheckDlgButton. Because controls are windows, the procedure can also manipulate them by
using window-management functions such as
EnableWindow and
SetFocus. The procedure can retrieve the window handle for a control by using the
GetDlgItem function.
The dialog box procedure can change the contents, state, and position of any
control as needed. For example, in a dialog box that contains a list box of
filenames and an Open button, the procedure can disable the Open button until the
user selects a file from the list. In this example, the dialog box template
specifies the WS_DISABLED style for the Open button and Windows automatically
disables the button when creating it. When the dialog box procedure receives a
notification message from the list box indicating that the user has selected a file,
the procedure calls the
EnableWindow function to enable the Open button.
If the application creates the dialog box by using one of the functions
DialogBoxParam,
DialogBoxIndirectParam,
CreateDialogParam, or
CreateDialogIndirectParam, the
lParam parameter for the WM_INITDIALOG message contains the extra parameter passed
to the function. Applications typically use this extra parameter to pass the
address of additional initialization information to the dialog box procedure, but
the dialog box procedure must determine the meaning of the parameter. If the
application uses another function to create the dialog box, Windows sets the
lParam parameter to NULL.
Before returning from the
WM_INITDIALOG message, the procedure should determine whether it should set the input focus
to a given control. If the dialog box procedure returns TRUE, Windows
automatically sets the input focus to the control whose window handle is in the
wParam parameter. If the control receiving the default focus is not appropriate, it
can set the focus to the appropriate control by using the
SetFocus function. If the procedure sets the input focus, it must return FALSE to
prevent Windows from setting the default focus. The control receiving the default
input focus is always the first control given in the template that is visible,
not disabled, and has the WS_TABSTOP style. If no such control exists, Windows
sets the default input focus to the first control in the template.
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