SelectObject function
Applies to: desktop apps only
The SelectObject function selects an object into the specified device context (DC). The new object replaces the previous object of the same type.
Syntax
HGDIOBJ SelectObject( __in HDC hdc, __in HGDIOBJ hgdiobj );
Parameters
- hdc [in]
-
A handle to the DC.
- hgdiobj [in]
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A handle to the object to be selected. The specified object must have been created by using one of the following functions.
Object Functions - Bitmap
CreateBitmap, CreateBitmapIndirect, CreateCompatibleBitmap, CreateDIBitmap, CreateDIBSection
Bitmaps can only be selected into memory DC's. A single bitmap cannot be selected into more than one DC at the same time.
- Brush
CreateBrushIndirect, CreateDIBPatternBrush, CreateDIBPatternBrushPt, CreateHatchBrush, CreatePatternBrush, CreateSolidBrush
- Font
- Pen
- Region
CombineRgn, CreateEllipticRgn, CreateEllipticRgnIndirect, CreatePolygonRgn, CreateRectRgn, CreateRectRgnIndirect
Return value
If the selected object is not a region and the function succeeds, the return value is a handle to the object being replaced. If the selected object is a region and the function succeeds, the return value is one of the following values.
| Value | Meaning |
|---|---|
| SIMPLEREGION | Region consists of a single rectangle. |
| COMPLEXREGION | Region consists of more than one rectangle. |
| NULLREGION | Region is empty. |
If an error occurs and the selected object is not a region, the return value is NULL. Otherwise, it is HGDI_ERROR.
Remarks
This function returns the previously selected object of the specified type. An application should always replace a new object with the original, default object after it has finished drawing with the new object.
An application cannot select a single bitmap into more than one DC at a time.
ICM: If the object being selected is a brush or a pen, color management is performed.
Examples
For an example, see Setting the Pen or Brush Color.
Requirements
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Minimum supported client | Windows 2000 Professional |
|---|---|
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Minimum supported server | Windows 2000 Server |
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See also
- Device Contexts Overview
- Device Context Functions
- CombineRgn
- CreateBitmap
- CreateBitmapIndirect
- CreateBrushIndirect
- CreateCompatibleBitmap
- CreateDIBitmap
- CreateDIBPatternBrush
- CreateEllipticRgn
- CreateEllipticRgnIndirect
- CreateFont
- CreateFontIndirect
- CreateHatchBrush
- CreatePatternBrush
- CreatePen
- CreatePenIndirect
- CreatePolygonRgn
- CreateRectRgn
- CreateRectRgnIndirect
- CreateSolidBrush
- SelectClipRgn
- SelectPalette
Send comments about this topic to Microsoft
Build date: 3/7/2012
CGdiObject::~CGdiObject()
in c:\Program Files\Microsoft Visual Studio 9.0\VC\atlmfc\include\afxwin1.inl,Line 107,It is quite clear that gdi objects need to be deleted. That because you are supposed NOT to leave any of your own created objects selected in one given DC. However,there is an window style that forces windows not to change the DC associated with a window as long as it exists: CS_OWNDC....
So the basic rule must be:
If it is selected in an DC,YOU MUST NOT DeleteObject, if it is not selected,then YOU MUST DeleteObject.
Consequently, if you want to deallocate an MFC CGdiObject-derived object such as an CBitmap you must first deselect it by selecting another CGdiObject or an saved HGDIOBJ(from an previous SelectObject()). Keep in mind that MFC CGdiObject* objects returned by SelectObject() are automatically deleted by mfc in its OnIdle(), so it would be safer to save an handle (HGDIOBJ) rather than an CGdiObject if you use CS_OWNDC.
If you do not have CS_OWNDC added to your window, then you must not preserve(save in member variables) in your class any of the returned GDI handles or objects passed the end of your message handler function(like OnDraw,OnPaint) , because on the next call of the message handler (OnDraw,OnPaint) it is quite possible to get another HDC(or CDC*),totally different than in the one in the previous call of the handler.
- 6/14/2011
- Anonymous7957
- 6/14/2011
- Anonymous7957
Additionally, since your code did not create that specific object yourself, another code fragment is responsible for deselecting and deleting it and deleting the same resource twice is usually an error.
- 1/24/2011
- DRFGHDE
When I use SelectObject, I normally restore the original object to the selection
savedObject = SelectObject(...)
...
SelectObject(savedObject)
Do I need to call DeleteObject() on savedObject in this case? As far as I could find out from the web the answer is no. SelectObject() doesn't increment the reference count.
- 10/19/2010
- Tim Lovell-Smith
