Child and Popup Windows, Dialog Boxes

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Child and Popup Windows, Dialog Boxes
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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.

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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.

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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.

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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

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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_USER1  / tell child
  window to maximize /
• define WM_MYMINCHILD    WM_USER2  / tell child
  window to minimize /

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Child Window Example

• child.cpp

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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

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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

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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 are predefined (template
  --a resource)
• How it does is determined by a "Dialog box
  procedure Destroyed immediately after use

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Rule of Thumb Dialog Boxes vs.programmer-defined
child windows

• Dialog box For simple popup windows that use
  normal window controls and do little painting on
  the client area
• Popup/child windows Use when extensive painting
  or nonstandard behavior needed
• Main advantage of dialog boxes
• Ease of construction with the dialog box editor
• Ease of communicating with its controls

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Steps in Using

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

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Steps in Using

• 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 this
  procedure
• 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

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Types of Dialog Boxes

• Modal
• Modeless
• System Modal

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Modal

• While visible, user can't switch back to parent
  window
• (Can change to other apps)
• User must explicitly end dialog box
• Typically by clicking "OK" or "CANCEL" buttons
  inside
• Most common type of dialog box
• Example "About" box available with most Windows
  apps
• Message Boxes are simple Modal Dialog Boxes

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System Modal

• A variety of modal dialog box
• With these user can't switch to other
  applications while dialog box is active
• A throwback to Win16

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Modeless

• User can switch between dialog box and the parent
  window
• More like popup windows
• Used when dialog box must be visible while user
  interacts with the parent
• Example dialog box resulting from "Find" or
  "Replace" menu item of many Windows apps

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Steps in Designing, Creating, Using a Modal
Dialog Box

• 1. Determine child window controls needed inside
• 2. Design dialog box template (easiest with
  dialog box editor)
• 3. Write message-processing function
• 4. Activate dialog box by calling DialogBox()
• Typically in response to menu item selection in
  WndProc()
• 5. Resulting dialog box stays on screen until
  call to EndDialog()
• from inside dialog box function

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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 its messages
• A callback function

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DialogBox()

• Creates modal dialog box from app's dialog box
  template resources
• Displays dialog box switches msg-processing to
  it
• Control returned when its msg-processing function
  terminates dialog box
• By calling EndDialog()

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WM_INITDIALOG Message

• Like an ordinary window's WM_CREATE message
• Processed before window (dialog box) is made
  visible
• Good place to put dialog box initialization code

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EndDialog()

• Destroys dialog box
• Returns control to function (WndProc()) that
  called 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 to
  calling program

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User Interaction with DialogBox Controls

• WM_COMMAND message
• LOWORD(wParam) contains control ID (as usual)
• lParam, wParam contain message data (as usual)

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Exchanging Data with a Dialog Box

• Exchanging data between dialog box function and
  app's WndProc()
• SendMessage() could be used to send message to
  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)

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Exchanging Data with a Dialog Box (contd)

• Both functions can be combined using
  SendDlgItemMessage()
• SendDlgItemMessage(hDlg, controlID, Msg, wParam,
  lParam)
• Sends Msg to control whose ID is controlID

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Example

• dlg2.cpp

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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

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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.

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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.

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Some Common Dialog Box functions

• ChooseColor(CHOOSECOLOR cc)
• ChooseFont(CHOOSEFONT cf)
• GetOpenFileName(OPENFILENAME ofn)
• GetSaveFileName(OPENFILENAME ofn)
• FindText(FINDREPLACE ft)