User and Graphics Device Interface Objects - Win32 Programmer's Reference

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User and Graphics Device Interface Objects

User and GDI objects support only one handle per object. Processes cannot inherit or duplicate handles to user or GDI objects.

Handles to user objects are public to all processes. That is, any process can use the user object handle, provided that the process has access to the object as defined by user security. For more information about security, see Security.

Handles to GDI objects are private to a process. That is, only the process that created the GDI object can use the object handle.

In the following illustration, an application creates a window object. The CreateWindow function creates the window object and returns an object handle.

After the window object has been created, the application can use the window handle to display or change the window. The handle remains valid until the window object is destroyed.

In the next illustration, the application destroys the window object. The DestroyWindow function removes the window object from memory, which invalidates the window handle.

The following table lists the Windows user objects and each object's creator and destructor functions. The creator functions either create the object and an object handle or simply return the existing object handle. The destructor functions remove the object from memory, which invalidates the object handle.

Note that the window station and desktop objects are created and maintained by the system; applications cannot delete these objects.

User Objects

Object	Creator function	Destructor function
Accelerator table	CreateAcceleratorTable	DestroyAcceleratorTable
Cursor	CreateCursor, LoadCursor, GetCursor, SetCursor	DestroyCursor
DDE conversation	DdeConnect, DdeConnectList, DdeQueryNextServer, DdeReconnect	DdeDisconnect, DdeDisconnectList
Desktop	GetThreadDesktop
Hook	SetWindowsHook, SetWindowsHookEx	UnhookWindowsHook, UnhookWindowsHookEx
Menu	CreateMenu, CreatePopupMenu, GetMenu, GetSubMenu, GetSystemMenu, LoadMenu, LoadMenuIndirect	DestroyMenu
Window	CreateWindow, CreateWindowEx, CreateDialogParam, CreateDialogIndirectParam, CreateMDIWindow, FindWindow, GetWindow, GetClipboardOwner, GetDesktopWindow, GetDlgItem, GetForegroundWindow, GetLastActivePopup, GetOpenClipboardWindow, GetTopWindow, WindowFromDC, WindowFromPoint, and others	DestroyWindow
Window position	BeginDeferWindowPos	EndDeferWindowPos
Window station	GetProcessWindowStation

The following table lists the Windows GDI objects and each object's creator and destructor functions. The creator functions either create the object and an object handle or simply return the existing object handle. The destructor functions remove the object from memory, which invalidates the object handle.

GDI Objects

Object	Creator function	Destructor function
Bitmap	CreateBitmap, CreateBitmapIndirect, CreateCompatibleBitmap, CreateDIBitmap, CreateDIBSection, CreateDiscardableBitmap	DeleteObject
Brush	CreateBrushIndirect, CreateDIBPatternBrush, CreateDIBPatternBrushPt, CreateHatchBrush, CreatePatternBrush, CreateSolidBrush	DeleteObject
Font	CreateFont, CreateFontIndirect	DeleteObject
Palette	CreatePalette	DeleteObject
Pen	CreatePen, CreatePenIndirect	DeleteObject
Extended pen	ExtCreatePen	DeleteObject
Region	CombineRgn, CreateEllipticRgn, CreateEllipticRgnIndirect, CreatePolygonRgn, CreatePolyPolygonRgn, CreateRectRgn, CreateRectRgnIndirect, CreateRoundRectRgn, ExtCreateRegion, PathToRegion	DeleteObject
Device context (DC)	CreateDC, GetDC	DeleteDC, ReleaseDC
Memory DC	CreateCompatibleDC	DeleteDC
Metafile	CloseMetaFile, CopyMetaFile, GetMetaFile, SetMetaFileBitsEx	DeleteMetaFile
Metafile DC	CreateMetafile	CloseMetaFile
Enhanced metafile	CloseEnhMetaFile, CopyEnhMetaFile, GetEnhMetaFile, SetEnhMetaFileBits	DeleteEnhMetaFile
Enhanced-metafile DC	CreateEnhMetaFile	CloseEnhMetaFile

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