Child and Popup Windows , Dialog Boxes

1. Child and Popup Windows,Dialog Boxes

2. Child Windows • sometimes we need to create custom windows • The most common type of custom window is called a child window • attached to its parent • only visible if its parent is visible • always on top of its parent • If the parent is destroyed, the child window also is destroyed.

3. Child windows usage • to deal with a specific task, e.g., getting input from the user • programming tool to break up a large screen area into smaller portions , each with its own message- processing function.

4. Creating a child window • Register a new window class for the child (RegisterClass()). • Create the child window using CreateWindow() with WS_CHILD style. • Write a separate message-processing function for the child window.

5. Sending messages to a child window • We can use SendMessage() to send messages to a child window • We need to specify the child window's handle and the message ID with its parameters • Frequently the message ID that is used is WM_USER • defined in Windows.h as a number which is greater than any of the predefined Windows messages

6. USER messages • We can use WM_USER and above to define messages for any type of activity • For example • #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 */

7. Child Window Example • child.cpp

8. Popup Windows • a type of child window that is not physically attached to its parent • can be positioned anywhere on screen • handy if the user needs to move things around on the screen • ideal for applications that have multiple independent sections, such as a communications program which supports a number of simultaneous terminal sessions

9. Creating Popup Windows • Popup windows are created with CreateWindow() • The WS_POPUP style (which is mutually exclusive with WS_CHILD) is used • Coordinates are interpreted as screen coordinates, not as client-area coordinates of the parent window

10. Dialog Boxes • Popup child windows created by Windows • Used for special-purpose input & output • Principal I/O mechanism in Windows • Contain several child window controls • Layout & what it does is are predefined(a resource template) • How it does is determined by a "Dialog box procedure“Destroyed immediately after use

11. Rule of Thumb: Dialog Boxes vs.programmer-defined child windows • Dialog box: For simple popup windows thatuse normal window controls and do littlepainting on the client area • Popup/child windows: Use when extensivepainting or non-standard behavior needed • Main advantage of dialog boxes: • Ease of construction with the dialog box editor • Ease of communicating with its controls

12. Steps in using dialogs: • 1. Set up the template in the resources(.rc file) • Specifies controls used, their style/layout • Can be prepared "visually" with VisualStudio dialog box editor • Or "manually" with a text editor

13. Steps in using dialogs: • 2. Write the dialog box procedure • Code to carry out dialog box's tasks • Placed in .cpp file • Provides message-processing capability • Messages from controls handled inside thisprocedure • Messages can be sent to the dialog box • A callback function like main window procedure WndProc() • But not the same • Part of the callback is inside Windows • It interprets some keystrokes (tab) • It calls our procedure

14. Types of Dialog Boxes • Modal • Modeless

15. Modal • While visible, user can't switch back to parentwindow • (Can change to other apps) • User must explicitly end dialog box • Typically by clicking "OK" or "CANCEL" buttonsinside • Most common type of dialog box • Example: "About" box available with mostWindows apps • Message Boxes are simple Modal Dialog Boxes

16. Modeless • User can switch between dialog box andthe parent window • More like popup windows • Used when dialog box must be visiblewhile user interacts with the parent • Example: dialog box resulting from"Find" or "Replace" menu itemof many Windows apps

17. Steps in designing, creating, using a Modal Dialog Box: 1. Determine child window controls needed inside 2. Design dialog box template (easiest with dialogbox editor) 3. Write message-processing function 4. Activate dialog box by calling DialogBox() • Typically in response to menu item selection inWndProc() 5. Resulting dialog box stays on screen until callto EndDialog() • from inside dialog box function

18. DialogBox() • Parameters: • 1. App's instance handle • 2. Dialog box ID name • Specified in dialog box template when .rc file created • 3. Handle of dialog box's parent window • 4. Address of dialog box function that will process itsmessages • A callback function

19. DialogBox() • Creates modal dialog box from app's dialog boxtemplate resources • Displays dialog box & switches msg-processing to it • Control returned when its msg-processing functionterminates dialog box • By calling EndDialog() ;

20. WM_INITDIALOG Message • Likean ordinary window'sWM_CREATE message • Processed before window (dialog box) ismade visible • Good place to put dialog boxinitialization code

21. EndDialog() • Destroys dialog box • Returns control to function (WndProc()) thatcalled DialogBox() • Parameters: • 1. window handle passed to dialog box function(hDlg) • 2. integer value returned by DialogBox() • Way of getting info from dialog box function tocalling program

22. User Interaction with DialogBox Controls • WM_COMMAND message • LOWORD(wParam) contains control ID (asusual) • lParam, wParam contain message data (asusual)

23. Exchanging Data with a Dialog Box • Exchanging data between dialog box functionand app's WndProc() • SendMessage() could be used to send messageto control inside, BUT: • Need to know control's handle • Not known since Windows creates the controls • IDs are known--specified in resource template • Use GetDlgItem() to get control's handle: • hControl = GetDlgItem(hDlg, controlID ); • Then SendMessage(hControl, Msg, wParam,lParam);

24. Exchanging Data with a Dialog Box (cont’d) • Both functions can be combined usingSendDlgItemMessage(): • SendDlgItemMessage(hDlg, controlID,Msg, wParam, lParam); • Sends Msg to control whose ID is controlID

25. Example • dlg2.cpp

26. Common dialog boxes • a library of functions that invoke standard dialog boxes • opening/saving files • searching/replacing text • choosing colors • choosing fonts • getting/changing information on printers

27. How do they work? • A single function from the library is called, instead of having to set up a .rc template and write a dialog box procedure • For each common dialog box, COMMDLG.DLL provides the standard template and the default dialog box procedure which processes messages from the dialog box controls.

28. Steps in Setting Up and Using a Common Dialog box • Initialize the fields of a structure with data needed by the dialog box. • Set up a pointer to a structure in the library function. • Call the library function, passing it the pointer. • The library function creates/displays the dialog box. • The user interacts with the dialog box and causes it to be removed. • The library function returns control to the application. • The application retrieves the information returned in the structure.

29. Some Common Dialog Box functions • ChooseColor(CHOOSECOLOR* cc) • ChooseFont(CHOOSEFONT* cf) • GetOpenFileName(OPENFILENAME* ofn) • GetSaveFileName(OPENFILENAME* ofn) • FindText(FINDREPLACE* ft)