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Scroll Window Control
Scroll window (ScrollWnd) control is a container control with scroll bars to
browse children windows in it. Its basic usage is to place child controls, so
make the user can check and operate many controls in a window by scroll bars.
Certainly, ScrollWnd can also be used to do many other things, and it is easy
to be customized. In the end of this chapter, we will see a example which uses
ScrollWnd as a picture viewer.
In an application, calling CreateWindow function with CTRL_SCROLLWND as the
control class name can create ScrollWnd control.
Scrollable Window
ScrollWnd control and ScrollView control discussed in the next chapter are
both scrollable window controls, and have many similarities. A scrollable
window comprises a control window (visible area) with scroll bar and content
area, as shown in Figure 1. When scroll bar is used to move the display content
area, horizontal position value or vertical position value of content area will
change. Size of content area can be controlled by application, but cannot be
smaller than visible area.
Figure 1 A scrollable window
General Scroll Window Messages
ScrollWnd and ScrollView control all respond to some general scroll window
messages, including getting and setting content range of scroll window, setting
scroll value of scroll bar, getting and setting the current position of content
area, getting and setting size of visible area, etc.
Get/Set the Range of Content Area and Visible Area
SVM_SETCONTRANGE message is used to set the size of the content area of a
scroll window:
Here, cont_w and cont_h are the width and the height of content area to be
set respectively. If cont_w or cont_h is negative, content area will not
change; if the content area width (height) to be set is less than visible area
width (height), the content area width (height) after set will equal to the
visible area width (height).
SVM_SETCONTWIDTH message and SVM_SETCONTHEIGHT message are used to set the
width and the height of a scroll window respectively:
SVM_GETCONTWIDTH, SVM_GETCONTHEIGHT, SVM_GETVISIBLEWIDTH and
SVM_GETVISIBLEHEIGHT message are used to get the content area width and
height and the visible area width and height respectively.
Get Position Information and Set Current Position
SVM_GETCONTENTX and SVM_GETCONTENTY messages are used to get the current
position value of the content area:
SVM_SETCONTPOS message is used to set the current position value of the
content area, i.e. move the content area to a specified position in the visible
area:
SVM_MAKEPOSVISIBLE message is used to make a position point in the content
area visible:
If this position point is invisible originally, while it becomes visible by
using SVM_MAKEPOSVISIBLE message, the position point will locate in the up
edge of visible area (previous position point is above visible area) or down
edge of visible area (previous position point is below visible area).
Get/Set Scroll Properties
SVM_GETHSCROLLVAL and SVM_GETVSCROLLVAL messages are used to get the
current horizontal and vertical line values of the scroll window (the scroll
values when clicking the scroll arrow); VM_GETHSCROLLPAGEVAL and
SVM_GETVSCROLLPAGEVAL messages are used to get the current horizontal and
vertical page values of the scroll window (the scroll values when clicking the
scroll page):
SVM_SETSCROLLVAL message is used to set the horizontal and (or) vertical line
value of a scroll window; wParam argument is the horizontal line value and
lParam is the vertical line value; if the horizontal (vertical) line value is
zero or negative value, the current horizontal (vertical) line value of the
scroll window will not change:
SVM_SETSCROLLPAGEVAL is used to set the horizontal and (or) vertical page
value of a scroll window; wParam argument is the horizontal page value and
lParam is the vertical page value; if the horizontal (vertical) page value is
zero or negative value, the current horizontal (vertical) page value of the
scroll window will not change:
Message of Scroll Window Control
Add Child Control
It should be noted that adding controls to ScrollWnd control will not change
the content area range of the scroll window, and if the position of a child
control locates beyond the current range of the content area, you cannot see
the control in the content area. Therefore, generally, you should use
SVM_SETCONTRANGE message to set the range of the content area before adding
child controls, to make it suitable for display of controls to be added.
Except sending SVM_ADDCTRLS message to add child controls after ScrollWnd
control is created, you can also make ScrollWnd automatically add the child
controls after passing the pointer to a CONTAINERINFO structure in
dwAddData argument, when calling CreateWindow function to create the
ScrollWnd control creates ScrollWnd:
The field controlnr is the number of controls, controls points to a CTRLDATA
control array; Additional data is passed through dwAddData field in
CONTAINERINFO structure.
SVM_RESETCONTENT message is used to reset a ScrollWnd control, including
destroying its child controls and set the range and the position values of the
content area to be the default values:
Get Handle of Child Control
SVM_GETCTRL can be used to get the handle of a child control in a ScrollWnd
control:
SVM_GETFOCUSCHILD message can be used to get the child control gaining
keyboard focus in a ScrollWnd control:
Container (Content) Window Procedure
The window in which child control is contained in a scroll window is called the
container window, i.e. content window (area). You can use
SVM_SETCONTAINERPROC message to set a new container window procedure, to
achieve the goal of customizing the scroll window for an application:
The parameter lParam is the container window process defined by your
application, and this window procedure should call the default container window
procedure function DefaultContainerProc by default:
Additionally, an application can specify user-defined container window
procedure by user_proc field of CONTAINERINFO aforementioned.
Sample Program
We illustrate the method of using ScrollWnd control to construct a simple
picture viewer using code in List 1. Please refer to scrollwnd.c program in
this guide sample program packet mg-samples for the complete source code of
this program.
List 1 Example program for ScrollWnd control
This simple picture viewer can be used to view a picture by using scrollbar,
and to enlarge and shrink the picture. The picture viewer sets a new container
window procedure function by sending SVM_SETCONTAINERPROC message, and draws
the picture in MSG_PAINT message.Running effect of the program is shown as
Figure 2.
Figure 2 A simple picture explorer
-- Main.XiaodongLi - 26 Oct 2009
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