Generally, an application defines a dialog template in its resource file and loads the dialog window by calling the WinLoadDlg function or the WinDlgBox function (which calls WinLoadDlg). The dialog window is created as an invisible window unless the window style WS_VISIBLE is specified in the dialog template. A WM_INITDLG message is sent to the dialog procedure before WinLoadDlg returns. As each control defined in the template is created, the dialog procedure might receive various control notifications before the function returns. WinLoadDlg returns a handle to the dialog window immediately after creating a dialog window.

In general, it is a good idea to define a dialog window as invisible, since this allows for optimization. For example, an experienced user might type ahead rapidly, anticipating the processing of a dialog-window command. In such a case, there is no need to display the dialog window, because the user has finished the interaction before the window can be displayed. This is how the WinProcessDlg function works-it does not display a dialog window while there still are WM_CHAR messages in the input queue; it processes the WM_CHAR messages before displaying the dialog window.

As control windows in a dialog window are created from the template, strings in the template are processed by the WinSubstituteStrings function. Any WM_SUBSTITUTESTRING messages are sent to the dialog procedure before WinLoadDlg returns.

When child windows of a dialog window are created, WinSubstituteStrings is used so child windows can make substitutions in their window text. If any child-window text string contains the percent sign (%) substitution character, the length of the text string is limited to 256 characters after it is returned from the substitution.