System Window Classes - Window Programming - Lecture Slides, Slides of Windows Programming

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Windows Programming

Lecture 12

System Window Classes

• Till now, we registered a window class before creating a window. A number of window classes are pre-registered / pre-coded in Windows, and their window procedures also are pre-written
• No call to RegisterClass() before creating

such a window

Window Classes

• User defined window classes are automatically unregistered when application using those classes terminates.
• System classes cannot be unregistered by user processes.

System/Pre-defined Window Classes

(to be used by user processes only)

• Button o pushbutton o autocheckbox o radio etc.
• ComboBox
• Edit
• ListBox
• ScrollBar
• Static

Styles of system Window class

BUTTON

BS_AUTOCHECKBOX BS_AUTORADIOBUTTON BS_PUSHBUTTON BS_RADIOBUTTON BS_DEFPUSHBUTTON … … …

Example: System Window Classes

hWnd = CreateWindow( "BUTTON", "Virtual University", BS_RADIOBUTTON | WS_VISIBLE | WS_OVERLAPPEDWINDOW | WS_CAPTION, 50, 50, 200, 100, NULL, NULL, hInstance, NULL);

while(GetMessage(&msg, NULL, 0, 0) > 0) { if(msg.message == WM_LBUTTONUP) { DestroyWindow(hWnd); PostQuitMessage(0); } DispatchMessage(&msg); }

GetWindowLong( )

LONG GetWindowLong(

HWND hWnd , // handle to window int nIndex // offset of value to retrieve

);

SetWindowLong( )

The SetWindowLong() function changes an

attribute of the specified window.

Sub-classing

Sub-classing allows you to change the behavior of an existing window, typically a control, by inserting a message map to intercept the window's messages. For example, suppose you have a dialog box with an edit control that you want to accept only non-numeric characters. You could do this by intercepting WM_CHAR messages destined for the edit control and discarding any messages indicating that a numeric character has been entered.

Sub-classing

Sub-classing is of two types:

• Just for one window
• For all windows in the application created after substitution of the window procedure

GetClassLong()

The GetClassLong() function retrieves the specified 32-bit (long) value from the WNDCLASS structure associated with the specified window.

GetClassLong()

LONG GetClassLong(

HWND hWnd, // handle to window

int nIndex // offset of value to retrieve

);

SetClassLong()

LONG SetClassLong(

HWND hWnd, // handle to window

int nIndex, // offset of value to set

LONG dwNewLong // new value

Difference Between

SetWindowLong() and SetClassLong()

• In SetWindowLong() , behavior of a single window is modified.
• In SetClassLong() , behavior of the window class is modified