Dialog Box Controls

The template specifies the position, width, height, style, identifier, and window class for each control in the dialog box. Windows creates each control by passing this data to the CreateWindowEx function. Controls are created in the order they are given in the template. The template should specify the appropriate number, type, and order of controls to ensure that the user can enter the input needed to complete the command associated with the dialog box.

For each control, the template specifies style values that define the appearance and operation of the control. Every control is a child window and therefore must have the WS_CHILD style. To ensure that the control is visible when the dialog box is displayed, each control must also have the WS_VISIBLE style. Other commonly used window styles are WS_BORDER for controls that have optional borders, WS_DISABLED for controls that should be disabled when the dialog box is initially created, and WS_TABSTOP and WS_GROUP for controls that can be accessed using the keyboard. The WS_TABSTOP and WS_GROUP styles are used in conjunction with the dialog keyboard interface described later in this topic.

The template may also specify control styles specific to the control's window class. For example, a template that specifies a button control must give a button control style such as BS_PUSHBUTTON or BS_CHECKBOX. Windows passes the control styles to the control window procedure through the WM_CREATE message, allowing the procedure to adapt the appearance and operation of the control.

Windows converts the position coordinates and the width and height measurements from dialog base units to pixels, before passing these to CreateWindowEx. When Windows creates a control, it specifies the dialog box as the parent window. This means Windows always interprets the position coordinates of the control as client coordinates, relative to the upper left corner of the dialog box's client area.

The template specifies the window class for each control. A typical dialog box contains controls belonging to the predefined control window classes, such as the button and edit control window classes. In this case, the template specifies window classes by supplying the corresponding predefined atom values for the classes. When a dialog box contains a control belonging to a custom control window class, the template gives the name of that registered window class or the atom value currently associated with the name.

Each control in a dialog box must have a unique identifier to distinguish it from other controls. Controls send information to the dialog box procedure through WM_COMMAND messages, so the control identifiers are essential for the procedure to determine which control sent a given message. The only exception to this rule are control identifiers for static controls. Static controls do not require unique identifiers because they send no WM_COMMAND messages.

To permit the user to close the dialog box, the template should specify at least one push button and give it the control identifier IDCANCEL. To permit the user to choose between completing or canceling the command associated with the dialog box, the template should specify two push buttons, labeled OK and Cancel, with control identifiers of IDOK and IDCANCEL, respectively.

A template also specifies optional text and creation data for a control. The text typically provides labels for button controls or specifies the initial content of a static text control. The creation data is one or more bytes of data that Windows passes to the control window procedure when creating the control. Creation data is useful for controls that require more information about their initial content or style than is given by other data. For example, an application can use creation data to set the initial setting and range for a scroll bar control.

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