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User Interfaces

11.2 THREADS 2
11.2.2 W
11.3 WINDOWS 3
11.3.2 A
PPLICATION WINDOWS 4 Client Area 5 Nonclient Area 5
11.3.3 W
INDOW ATTRIBUTES 6 Class Name 6 Window Name 6 Window Style 7 Extended Window Style 7 Position 7 Size 8 Parent or Owner Window Handle 8 Menu Handle or Child-Window Identifier 9 Application Instance Handle 9 Creation Data 9 Window Handle 9
11.3.4 M
11.4.1 EDIT CONTROL 10
11.4.2 S
11.4.3 S
11.7.1 WM_SYSCOMMAND: 12
EXERCISE 14User Interfaces 2

11.1 Hierarchy of Windows

The basic building block for displaying information in the Microsoft® Windows™
graphical environment is the window. Microsoft Windows manages how each window
relates to all other windows in terms of visibility, ownership, and parent/child
relationship. Windows uses this relationship information when creating, painting,
destroying, sizing or displaying a window. A window can have many children’s and may
or may not have one parent. An example of windows is Notepad, calculator, word pad
etc, are all windows.
A window shares the screen with other windows, including those from other applications.
Only one window at a time can receive input from the user. The user can use the mouse,
keyboard, or other input device to interact with this window and the application that owns

11.2 Threads

A thread is basically a path of execution through a program. It is also the smallest unit of
execution that Win32 schedules. A thread consists of a stack, the state of the CPU
registers, and an entry in the execution list of the system scheduler. Each thread shares all
of the process’s resources.
A process consists of one or more threads and the code, data, and other resources of a
program in memory. Typical program resources are open files, semaphores, and
dynamically allocated memory. A program executes when the system scheduler gives one
of its threads execution control. The scheduler determines which threads should run and
when they should run. Threads of lower priority may have to wait while higher priority
threads complete their tasks. On multiprocessor machines, the scheduler can move
individual threads to different processors to “balance” the CPU load.
Each thread in a process operates independently. Unless you make them visible to each
other, the threads execute individually and are unaware of the other threads in a process.
Threads sharing common resources, however, must coordinate their work by using
semaphores or another method of inter process communication.
So a thread is a process that is part of a larger process or application. A thread can
execute any part of an application's code, including code that is currently being executed
by another thread. All threads share the
􀀹 Virtual Address space
􀀹 Global variables
􀀹 Operating system resources of their respective processes.
Threads are two types of threads.
User Interfaces 3
1. User-Interface Thread
2. Worker Thread

11.2.1 User-Interface Thread

In Windows, a thread that handles user input and responds to user events independently is
User-Interface Thread. User-interface thread own one or more windows and have its own
message queue. User-interface threads process messages, received from the system.

11.2.2 Worker Thread

A worker thread is commonly used to handle background tasks. Tasks such as calculation
and background printing are good examples of worker threads.

11.3 Windows

In a graphical Microsoft® Windows®-based application, a window is a rectangular area
of the screen where the application displays output and receives input from the user.
Therefore, one of the first tasks of a graphical Windows-based application is to create a
A window shares the screen with other windows, including those from other applications.
Only one window at a time can receive input from the user. The user can use the mouse,
keyboard, or other input device to interact with this window and the application that owns
A Window may further contain more windows inside it. For example lets take a
calculator, A calculator contains more windows in forms of buttons, radio buttons and
check boxes.
Every Window has its parent and zero or more siblings.
Top level window has desktop as its parent.

11.3.1 Desktop Window

When you start the system, it automatically creates the desktop window. The desktop
is a system-defined window that paints the background of the screen and serves
as the base for all windows displayed by all applications.
The desktop window uses a bitmap to paint the background of the screen. The pattern
created by the bitmap is called the desktop wallpaper. By default, the desktop window
uses the bitmap from a .bmp file specified in the registry as the desktop wallpaper.
The GetDesktopWindow function returns a handle to the desktop window.
A system configuration application, such as a Control Panel item, changes the desktop
wallpaper by using the SystemParametersInfo function with the wAction parameter set to
User Interfaces 4
SPI_SETDESKWALLPAPER and the lpvParam parameter specifying a bitmap file
name. SystemParametersInfo then loads the bitmap from the specified file, uses the
bitmap to paint the background of the screen, and enters the new file name in the registry.

11.3.2 Application Windows

Every graphical Microsoft® Windows®-based application creates at least one window,
called the main window that serves as the primary interface between the user and the
application. Most applications also create other windows, either directly or indirectly, to
perform tasks related to the main window. Each window plays a part in displaying output
and receiving input from the user.
When you start an application, the system also associates a taskbar button with the
application. The taskbar button contains the program icon and title. When the application
is active, its taskbar button is displayed in the pushed state.
An application window includes elements such as a title bar, a menu bar, the window
menu (formerly known as the system menu), the minimize button, the maximize button,
the restore button, the close button, a sizing border, a client area, a horizontal scroll bar,
and a vertical scroll bar. An application's main window typically includes all of these
components. The following illustration shows these components in a typical main

Figure 1 Windows Parts

User Interfaces 5 Client Area

The client area is the part of a window where the application displays output, such as text
or graphics. For example, a desktop publishing application displays the current page of a
document in the client area. The application must provide a function, called a window
procedure, to process input to the window and display output in the client area. For more
information, see Window Procedures. Nonclient Area

The title bar, menu bar, window menu, minimize and maximize buttons, sizing border,
and scroll bars are referred to collectively as the window's nonclient area. The system
manages most aspects of the nonclient area; the application manages the appearance and
behavior of its client area.
The title bar displays an application-defined icon and line of text; typically, the text
specifies the name of the application or indicates the purpose of the window. An
application specifies the icon and text when creating the window. The title bar also makes
it possible for the user to move the window by using a mouse or other pointing device.
Most applications include a menu bar that lists the commands supported by the
application. Items in the menu bar represent the main categories of commands. Clicking
an item on the menu bar typically opens a pop-up menu whose items correspond to the
tasks within a given category. By clicking a command, the user directs the application to
carry out a task.
The window menu is created and managed by the system. It contains a standard set of
menu items that, when chosen by the user, set a window’s size or position, closes the
application, or performs tasks.
The buttons in the upper-right corner affect the size and position of the window. When
you click the maximize button, the system enlarges the window to the size of the screen
and positions the window, so it covers the entire desktop, minus the taskbar. At the same
time, the system replaces the maximize button with the restore button. When you click
the restore button, the system restores the window to its previous size and position. When
you click the minimize button, the system reduces the window to the size of its taskbar
button, positions the window over the taskbar button, and displays the taskbar button in
its normal state. To restore the application to its previous size and position, click its
taskbar button. By clicking the close button, application exits.
The sizing border is an area around the perimeter of the window that enables the user to
size the window by using a mouse or other pointing device.
The horizontal scroll bar and vertical scroll bar convert mouse or keyboard input into
values that an application uses to shift the contents of the client area either horizontally or
vertically. For example, a word-processing application that displays a lengthy document
User Interfaces 6
typically provides a vertical scroll bar to enable the user to page up and down through the

11.3.3 Window Attributes

An application must provide the following information when creating a window. (With
the exception of the Window Handle, which the creation function returns to uniquely
identify the new window.)
Class Name
Window Name
Window Style
Extended Window Style
Parent or Owner Window Handle
Menu Handle or Child-Window Identifier
Application Instance Handle
Creation Data
Window Handle
These window attributes are described in the following sections. Class Name

Every window belongs to a window class. An application must register a window class
before creating any windows of that class. The window class defines most aspects of a
window's appearance and behavior. The chief component of a window class is the
window procedure, a function that receives and processes all input and requests sent to
the window. The system provides the input and requests in the form of messages. For
more information, see Window Classes, Window Procedures, and Messages and
Message Queues. Window Name

A window name is a text string that identifies a window for the user. A main window,
dialog box, or message box typically displays its window name in its title bar, if present.
A control may display its window name, depending on the control's class. For example,
buttons, edit controls, and static controls displays their window names within the
rectangle occupied by the control. However, list boxes, combo boxes, and static controls
do not display their window names.
To change the window name after creating a window, use the SetWindowText function.
This function uses the GetWindowTextLength and GetWindowText functions to retrieve
the current window-name string from the window.
User Interfaces 7 Window Style

Every window has one or more window styles. A window style is a named constant that
defines an aspect of the window's appearance and behavior that is not specified by the
window's class. An application usually sets window styles when creating windows. It can
also set the styles after creating a window by using the SetWindowLong function.
The system and, to some extent, the window procedure for the class, interpret the window
Some window styles apply to all windows, but most apply to windows of specific
window classes. The general window styles are represented by constants that begin with
the WS_ prefix; they can be combined with the OR operator to form different types of
windows, including main windows, dialog boxes, and child windows. The class-specific
window styles define the appearance and behavior of windows belonging to the
predefined control classes. For example, the SCROLLBAR class specifies a scroll bar
control, but the SBS_HORZ and SBS_VERT styles determine whether a horizontal or
vertical scroll bar control is created.
For lists of styles that can be used by windows, see the following topics:
Window Styles
Button Styles
Combo Box Styles
Edit Control Styles
List Box Styles
Rich Edit Control Styles
Scroll Bar Control Styles
Static Control Styles Extended Window Style

Every window can optionally have one or more extended window styles. An extended
window style
is a named constant that defines an aspect of the window's appearance and
behavior that is not specified by the window class or the other window styles. An
application usually sets extended window styles when creating windows. It can also set
the styles after creating a window by using the SetWindowLong function.
For more information, see CreateWindowEx. Position

A window's position is defined as the coordinates of its upper left corner. These
coordinates, sometimes called window coordinates, are always relative to the upper left
corner of the screen or, for a child window, the upper left corner of the parent window's
client area. For example, a top-level window having the coordinates (10,10) is placed 10
User Interfaces 8
pixels to the right of the upper left corner of the screen and 10 pixels down from it. A
child window having the coordinates (10,10) is placed 10 pixels to the right of the upper
left corner of its parent window's client area and 10 pixels down from it.
The WindowFromPoint function retrieves a handle to the window occupying a particular
point on the screen. Similarly, the ChildWindowFromPoint and
ChildWindowFromPointEx functions retrieve a handle to the child window occupying a
particular point in the parent window's client area. Although
ChildWindowFromPointEx can ignore invisible, disabled, and transparent child
windows, ChildWindowFromPoint cannot. Size

A window's size (width and height) is given in pixels. A window can have zero width or
height. If an application sets a window's width and height to zero, the system sets the size
to the default minimum window size. To discover the default minimum window size, an
application uses the GetSystemMetrics function with the SM_CXMIN and SM_CYMIN
An application may need to create a window with a client area of a particular size. The
AdjustWindowRect and AdjustWindowRectEx functions calculate the required size of a
window based on the desired size of the client area. The application can pass the resulting
size values to the CreateWindowEx function.
An application can size a window so that it is extremely large; however, it should not size
a window so that it is larger than the screen. Before setting a window's size, the
application should check the width and height of the screen by using GetSystemMetrics with the SM_CXSCREEN and SM_CYSCREEN flags. Parent or Owner Window Handle

A window can have a parent window. A window that has a parent is called a child
. The parent window provides the coordinate system used for positioning a child
window. Having a parent window affects aspects of a window's appearance; for example,
a child window is clipped so that no part of the child window can appear outside the
borders of its parent window. A window that has no parent, or whose parent is the
desktop window, is called a top-level window. An application uses the EnumWindows
function to obtain a handle to each of its top-level windows. EnumWindows passes the
handle to each top-level window, in turn, to an application-defined callback function,
A window can own, or be owned by, another window. An owned window always appears
in front of its owner window, is hidden when its owner window is minimized, and is
destroyed when its owner window is destroyed. For more information, see Owned
User Interfaces 9 Menu Handle or Child-Window Identifier

A child window can have a child-window identifier, a unique, application-defined value
associated with the child window. Child-window identifiers are especially useful in
applications that create multiple child windows. When creating a child window, an
application specifies the identifier of the child window. After creating the window, the
application can change the window's identifier by using the SetWindowLong function,
or it can retrieve the identifier by using the GetWindowLong function.
Every window, except a child window, can have a menu. An application can include a
menu by providing a menu handle either when registering the window's class or when
creating the window. Application Instance Handle

Every application has an instance handle associated with it. The system provides the
instance handle to an application when the application starts. Because it can run multiple
copies of the same application, the system uses instance handles internally to distinguish
one instance of an application from another. The application must specify the instance
handle in many different windows, including those that create windows. Creation Data

Every window can have application-defined creation data associated with it. When the
window is first created, the system passes a pointer to the data on to the window
procedure of the window being created. The window procedure uses the data to initialize
application-defined variables. Window Handle

After creating a window, the creation function returns a window handle that uniquely
identifies the window. A window handle has the HWND data type; an application must
use this type when declaring a variable that holds a window handle. An application uses
this handle in other functions to direct their actions to the window.
An application can use the FindWindow function to discover whether a window with the
specified class name or window name exists in the system. If such a window exists,
FindWindow returns a handle to the window. To limit the search to the child windows of
a particular application, use the FindWindowEx function.
The IsWindow function determines whether a window handle identifies a valid, existing
window. There are special constants that can replace a window handle in certain
functions. For example, an application can use HWND_BROADCAST in the
SendMessage and SendMessageTimeout functions, or HWND_DESKTOP in the
MapWindowPoints function.
User Interfaces 10

11.3.4 Multithread Applications

A Windows-based application can have multiple threads of execution, and each thread
can create windows. The thread that creates a window must contain the code for its
window procedure.
An application can use the EnumThreadWindows function to enumerate the windows
created by a particular thread. This function passes the handle to each thread window, in
turn, to an application-defined callback function, EnumThreadWndProc.
The GetWindowThreadProcessId function returns the identifier of the thread that created
a particular window.
To set the show state of a window created by another thread, use the ShowWindowAsync

11.4 Controls and Dialog Boxes

An application can create several types of windows in addition to its main window,
including controls and dialog boxes.
A control is a window that an application uses to obtain a specific piece of information
from the user, such as the name of a file to open or the desired point size of a text
selection. Applications also use controls to obtain information needed to control a
particular feature of an application. For example, a word-processing application typically
provides a control to let the user turn word wrapping on and off. For more information,
see Windows Controls.
Controls are always used in conjunction with another window—typically, a dialog box. A
dialog box is a window that contains one or more controls. An application uses a dialog
box to prompt the user for input needed to complete a command. For example, an
application that includes a command to open a file would display a dialog box that
includes controls in which the user specifies a path and file name. Dialog boxes do not
typically use the same set of window components as does a main window. Most have a
title bar, a window menu, a border (non-sizing), and a client area, but they typically do
not have a menu bar, minimize and maximize buttons, or scroll bars. For more
information, see Dialog Boxes.
A message box is a special dialog box that displays a note, caution, or warning to the
user. For example, a message box can inform the user of a problem the application has
encountered while performing a task. For more information, see Message Boxes.

11.4.1 Edit Control

An edit control is selected and receives the input focus when a user clicks the mouse
User Interfaces 11
inside it or presses the TAB key. After it is selected, the edit control displays its text (if
any) and a flashing caret that indicates the insertion point. The user can then enter text,
move the insertion point, or select text to be edited by using the keyboard or the mouse.
An edit control can send notification messages to its parent window in the form of
WM_COMMAND messages.

11.4.2 Static controls

A static control is a control that enables an application to provide the user with
informational text and graphics that typically require no response.
Applications often use static controls to label other controls or to separate a group
of controls. Although static controls are child windows, they cannot be selected.
Therefore, they cannot receive the keyboard focus.
Example of static control is a text in message box.

11.4.3 Scroll Bar

A window in a Win32®-based application can display a data object, such as a document
or a bitmap that is larger than the window's client area. When provided with a scroll bar,
the user can scroll a data object in the client area to bring into view the portions of the
object that extend beyond the borders of the window.
Scroll bar is of two types. Horizontal Scroll bars and Vertical Scroll bar.

11.5 Common Controls

The common controls are a set of windows that are implemented by the common control
, which is a dynamic-link (DLL) included with the Microsoft® Windows®
operating system. Like other control windows, a common control is a child window that
an application uses in conjunction with another window to perform I/O tasks.
Common controls are of these types.
Date Time Picker Control.
List View Control.
User Interfaces 12

11.6 Other user Interface Elements

The following are the user interface elements used in Windows.
Cursors (Mouse shape)
Icons (Windows Desktop Icons)
Bitmaps (Images with RGB color values.)
Accelerators (CTRL + S) Short Key combinations.

11.7 Windows Messages (brief description)

The following are the some of the windows messages


A window receives this message when the user chooses a command from the window
menu (formerly known as the system or control menu) or when the user chooses the
maximize button, minimize button, restore button, or close button.


This parameter specifies the type of system command requested. This parameter
can be one of the following values.


This parameter is the low-order word specifies the horizontal position of the
cursor, in screen coordinates, if a window menu command is chosen with the mouse.
Otherwise, this parameter is not used. The high-order word specifies the vertical position
of the cursor, in screen coordinates, if a window menu command is chosen with the
User Interfaces 13
mouse. This parameter is -1 if the command is chosen using a system accelerator, or zero
if using a mnemonic.

The Window Procedure (Switch Only)

wParam &= 0xFFF0; // lower 4-bits used by system
wParam = SC_MINIMIZE;//we handle this message and change it to
return DefWindowProc(hWnd, message, wParam, lParam);
wParam = SC_MAXIMIZE; //we handle this message and change it to
return DefWindowProc(hWnd, message, wParam, lParam);
case SC_CLOSE:
if(MessageBox(hWnd, "Are you sure to quit?",
"Please Confirm", MB_YESNO) == IDYES)
return DefWindowProc(hWnd, message, wParam, lParam);
case WM_DESTROY: PostQuitMessage(0); break;
default: return DefWindowProc(hWnd, message, wParam, lParam);

Swap Minimize/Maximize

Application swap buttons Maximize and Minimize with each other, as it is
described in windows procedure.
User Interfaces 14


In this lecture, we learnt more about windows, its hierarchy and types. We learnt
about windows types, these are owned windows and child windows. We must keep this
point in mind that owned windows and child windows have different concepts. Owned
windows have the handle of their owner windows, these handle make a chain of owned
windows. We read about the behavior of owned windows and owner windows. We knew
that if we bring some change to owner window then the owned windows will response on
some changes like minimize and destroying operations. We also knew about child
windows that these are the part of its parent’s client area. After we knew about threads
and their types, threads are two types one is User interface thread and second is working
thread. UI (User interface) thread is attached with user interfaces like windows, messages
and dialog boxes. We gained a little knowledge about controls. And after that we learnt
how to make a windows procedure with responses system menu including close,
maximize and minimize button.


1. Write down a code which able to
i. Create window on screen with default coordinates
ii. Show Edit control on top left corner in the client area.
iii. Display button besides the edit control, which contains text ‘Show
text on client area’
iv. After pressing button, text must display on the client area.
v. And when the user closes the application, it must show message
box which will be containing ‘Thanks for using my application’

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