VC++ Workshop
Session 5
R. Eckert
Child and Popup Windows
Predefined window controls (buttons, static text, etc.)--examples of child windows
OK if controls have exact features required
But sometimes custom child windows needed
Child Window--
Most common type of custom window
Always attached to parent window
Always on top of parent
Parent minimized child disappears
Reappears when parent restored
Parent destroyed child also destroyed
Used to deal with a specific task
e.g., getting user input
Can be used as programming tool to break large screen area into smaller pieces
Each has its own message-processing function
Popup window--
Same general properties as child window, but:
Not physically attached to parent
Can be positioned anywhere on screen
Handy if the user needs to move things around on client area
Creating and Using a Child Window--
1. Register a new window class for child using RegisterClass()
Could be done in WinMain(() or when needed in WndProc()
2. Create child window using CreateWindow()
Should have WS_CHILD style
3. Write separate message-processing function for child window
Sending Messages to a Child Window--
Use SendMessage() and specify:
Child window's handle
Obtained when the child window was created
Message ID & parameters
Can use WM_USER
Defined in Windows.h as a number not used by predefined messages
All higher numbers also unused by Windows
Can use WM_USER and above for any type of activity
Example--could have a header file containing:
#define WM_MYKILLCHILD WM_USER // tell child window to vanish
#define WM_MYMAXCHILD WM_USER+1 // tell child window to maximize
#define WM_MYMINCHILD WM_USER+2 // tell child window to minimize
Could be used in child's msg-processing function switch statement
Child windows can send messages to parent or to other child windows
THE CHILD EXAMPLE PROGRAM--
User clicks "Create" menu item
Child window appears with "Destroy Me" button and some text
User clicks "Send Message" menu
Caption on child window changes
User clicks "Destroy Me" button in child window
Child window disappears
Both parent and child window have a line of text displayed in client areas
Registering Child Window Class with RegisterClass()--
Message processing function: ChildProc()
Will receive messages from any windows based on this class
Class Icon: LoadIcon() loads standard IDI_APPLICATION icon
When child minimized, that icon will appear inside parent window
Cursor shape: LoadCursor() loads standard IDC_CROSS cursor
Background: LTGRAY_BRUSH background brush is used
Menu: None will be used in child windows based on this class
Creating the Child Window with CreateWindow()--
User clicks "Create" menu item (WM_COMMAND, IDM_CREATE)
Program's WndProc() executes:
if(!hChild)
hChild = CreateWindow ("ChildClass", "Child Window",
WS_CHILD | WS_THICKFRAME | WS_MINIMIZEBOX |
WS_MAXIMIZEBOX | WS_CAPTION | WS_SYSMENU,
10, 30, 200, 150, hWnd,
NULL, hInstance, NULL);
Logic allows only one child window at a time
Window style flags
Child window is sizable, iconifiable, maximizable, movable
Has its own system menu button
Sending a Message to the Child Window--
User clicks "Send Message" menu item
WndProc() uses SendMessage() to send a WM_USER msg to child window
ChildProc()'s response to WM_USER msg from parent:
Uses SetWindowText() to set its caption bar to "Got message from parent"
Other ChildProc() Actions--
Response to creation: uses CreateWindow() to create a "Destroy Me" pushbutton
3-deep nesting of windows:
Parent (main window)
Child window
Button Control
Response to expose events: outputs a line of text to child window client area
Response to user clicking the pushbutton:
Uses GetParent(hChild) to get the parent's window handle
Destroys itself with a call to DestroyWindow(hChild)
Sends a USER+1 msg to parent using handle obtained from GetParent()
WndProc()'s response to this:
Sets hChild to NULL so another child can be created
WndProc() also responds to expose events by outputting a line of text to main
window's client area
So text in both windows is visible whenever either is exposed
POPUP WINDOWS--
Main distinction--not restricted to the parent window's client area
Can appear anywhere on screen
Handy for small utility programs, e.g.:
Window that shows current cursor position in a painting program
Ideal for applications with multiple independent sections, e.g.:
Communications pgm with simultaneous terminal sessions in different popup windows
Create with CreateWindow()
WS_POPUP style (mutually exclusive with WS_CHILD)
Coordinates are screen coordinates (relative to upper lefthand corner of screen)
The Big Picture--
Child window behavior Main program window behavior
------------------------------- = -----------------------------------------
Parent window behavior Windows desktop behavior
Windows desktop is just another window (lacking title bar and border)
All running main program windows behave like children of desktop window
Using same code for main program windows and child windows
Keeps Windows system small
Gives the environment a consistent behavior