SelectObject()函数

SelectObject 
把一个对象(位图、画笔、画刷等)选入指定的设备描写叙述表。新的对象取代同一类型的老对象。

HGDIOBJ SelectObject(

  HDC hdc,         // handle to DC

  HGDIOBJ hgdiobj  // handle to object

);

 

參数

1. hdc 设备描写叙述表句柄(要加载的设备描写叙述表句柄)
2. hgdiobj 选择要加载的对象的句柄

但该对象的句柄必须使用下面函数创建才有效：

Bitmap(位图)          CreateBitmap, CreateBitmapIndirect, 
                            CreateCompatibleBitmap, CreateDIBitmap, 
                            CreateDIBSection 
Brush(画刷)           CreateBrushIndirect, eateDIBPatternBrush,  
                            CreateDIBPatternBrushPt, CreateHatchBrush,  
                            CreatePatternBrush, CreateSolidBrush 
Font(字体)              CreateFont, CreateFontIndirect

Pen(画笔)               CreatePen, CreatePenIndirect

Region(区域)             CombineRgn, CreateEllipticRgn,  
                               CreateEllipticRgnIndirect,  
                               CreatePolygonRgn, CreateRectRgn,  
                               CreateRectRgnIndirect 

返回值：假设选择对象不是区域而且函数运行成功，那么返回值是被代替的对象的句柄。假设选择对象是区域而且函数运行成功。返回例如以下一值；

 =======================================================

1、看MSDN中的解释：

Selects an object into the device context（选择一个对象到设备上下文中去）.

CPen* SelectObject(
   CPen* pPen
);
CBrush* SelectObject(
   CBrush* pBrush
);
virtual CFont* SelectObject(
   CFont* pFont
);
CBitmap* SelectObject(
   CBitmap* pBitmap
);
int SelectObject(
   CRgn* pRgn
);
CGdiObject* SelectObject(
   CGdiObject* pObject
);

 

參数：

pPen

A pointer to a CPen object to be selected.

pBrush

A pointer to a CBrush object to be selected.

pFont

A pointer to a CFont object to be selected.

pBitmap

A pointer to a CBitmap object to be selected.

pRgn

A pointer to a CRgn object to be selected.

pObject

A pointer to a CGdiObject object to be selected.

 

返回值：

A pointer to the object being replaced. This is a pointer to an object of one of the classes derived fromCGdiObject, such as CPen, depending on which version of the function is used.

 

返回一个指向被取代的对象的指针。

这个真正指向的对象是重载于CGdiObject类的一种。比方CPen。详细以来与所使用的函数版本号。

 

2、測试代码

void CDrawView::OnLButtonDown(UINT nFlags, CPoint point)
{
    // TODO: Add your message handler code here and/or call default
    m_ptBegin=point;//m_ptBegin是类的成员。类型为CPoint

    CView::OnLButtonDown(nFlags, point);
}

void CDrawView::OnLButtonUp(UINT nFlags, CPoint point)
{
    // TODO: Add your message handler code here and/or call default
    CPen pen(PS_SOLID, 1, RGB(255, 0, 0));
    CClientDC dc(this);
    CPen* pOldPen=dc.SelectObject(&pen);//保存原始的CPen。即黑色的CPen
    dc.MoveTo(m_ptBegin);
    dc.LineTo(point);
    dc.SelectObject(pOldPen);//恢复原始的CPen
    dc.MoveTo(m_ptBegin);
    dc.LineTo(point.x+100, point.y);
    CView::OnLButtonUp(nFlags, point);
}

 

3、执行结果：