SelectObject和DeleteObject 函数
Windows显示设备的属性,共有下面几种:位图、画刷、字体、画笔、区域。如果要设置它们到当前设备里,就需要使用SelectObject函数,比如上面介绍的字体设置,就会用到这个函数。当你创建一个位图时,这时Windows就会在内存里分配一块内存空间,用来保存位图的数据。当你创建字体时,也会分配一块内存空间保存字体。如果程序只是分配,而不去删除,就会造成内存使用越来越多,最后导到Windows这幢大楼倒下来。如果你忘记删除它,就造成了内存泄漏。因此,当你创建显示设备资源时,一定要记得删除它们啊,否则运行你的程序越长,就导致系统不稳定。记得使用DeleteObject函数去删除它们,把占用的内存释放回去给系统。
函数SelectObject和DeleteObject声明如下:
WINGDIAPI HGDIOBJ WINAPI SelectObject(__in HDC hdc, __in HGDIOBJ h);
WINGDIAPI BOOL WINAPI DeleteObject( __in HGDIOBJ ho);
hDC是当前设备的句柄。
h,ho是设备对象,其实它就是内存的地址。
调用这个函数的例子如下:
#001 //
#002 //界面显示输出.
#003 //
#004 //蔡军生2007/09/01 QQ:9073204 深圳
#005 //
#006 void CCaiWinMsg::OnDraw(HDC hDC)
#007 {
#008 //
#009 std::wstring strShow(_T("C++窗口类的实现,2007-09-04"));
#010
#011 //设置输出字符串的颜色.
#012 COLORREF crOld = SetTextColor(hDC,RGB(255,0,0));
#013
#014 RECT rcText;
#015 rcText.left = 10;
#016 rcText.top = 10;
#017 rcText.right = 300;
#018 rcText.bottom = 80;
#019
#020 //创建黑色的画刷,
#021 HBRUSH hbrush = CreateSolidBrush(RGB(0, 0, 0));
#022
#023 //用黑色的画刷填充四边形的颜色.
#024 FillRect(hDC,&rcText,hbrush);
#025
#026 //删除画刷.
#027 DeleteObject(hbrush);
#028
#029
#030 rcText.left = 10;
#031 rcText.top = 10;
#032 rcText.right = 300;
#033 rcText.bottom = 40;
#034
#035 //显示字符串在四边形的中间位置.
#036 DrawText(hDC,strShow.c_str(),(int)strShow.length(),&rcText,
#037 DT_CENTER|DT_VCENTER|DT_SINGLELINE|DT_END_ELLIPSIS);
#038
#039
#040 rcText.left = 10;
#041 rcText.top = 40;
#042 rcText.right = 300;
#043 rcText.bottom = 80;
#044 //设置透明背景
#045 int nOldMode = SetBkMode(hDC,TRANSPARENT);
#046
#047 //设置新字体.
#048 HGDIOBJ hOldFont = SelectObject(hDC,GetFont());
#049
#050 //显示字符串在四边形的中间位置.
#051 DrawText(hDC,strShow.c_str(),(int)strShow.length(),&rcText,
#052 DT_CENTER|DT_VCENTER|DT_SINGLELINE|DT_END_ELLIPSIS);
#053
#054 //恢复原来的字体.
#055 HGDIOBJ hFont = SelectObject(hDC,hOldFont);
#056 DeleteObject(hFont);
#057
#058 //恢复原来的模式.
#059 SetBkMode(hDC,nOldMode);
#060
#061 //恢复原来的颜色.
#062 SetTextColor(hDC,crOld);
#063 }
以上转自:http://blog.csdn.net/caimouse/archive/2007/09/05/1773850.aspx
////////////////////////////////////////////////
CFont font;
font.CreatePointFont(g_myFont,_T("宋体"));
GetDlgItem(IDC_STATIC_TITLE)->SetFont(&font);
CFont *pOldFont=pDC->SelectObject(&font);
DeleteObject(pOldFont);
//////////////////////////////////////////////////
BoundsChecker
发现有错误发生:Argument 1 in DeleteObject(字体对象句柄值) is still selected in to hDC 0x01010058
修改 :
//////////////////////////////////////////////////
//字体大小
CFont font;
font.CreatePointFont(g_myFont,_T("宋体"));
CFont *pOldFont=pDC->SelectObject(&font);
GetDlgItem(IDC_STATIC_TITLE)->SetFont(&font);//为控件附上字号
pDC->SelectObject(pOldFont);
DeleteObject(font);//释放资源
//////////////////////////////////////////////////
另一列:
//////////////////////////////////////////////////
CRect rect;
CDC* pDC=GetDC();
GetWindowRect(&rect);
CPen spen;
//被选中,显示红色,否则显示灰色
if(bIsSelect)spen.CreatePen(PS_SOLID,3,RGB(0,255,0));
else spen.CreatePen(PS_SOLID,3,RGB(192,192,192));
pDC->SelectObject(&spen);
pDC->SelectObject(GetStockObject(NULL_BRUSH));//选择透明填充
pDC->Rectangle(0,0,rect.Width()-3,rect.Height()-3);
ReleaseDC(pDC);
//////////////////////////////////////////////////
修改:
//////////////////////////////////////////////////
CRect rect;
CDC* pDC=GetDC();
GetWindowRect(&rect);
CPen spen;
//被选中,显示红色,否则显示灰色
if(bIsSelect)spen.CreatePen(PS_SOLID,3,RGB(0,255,0));
else spen.CreatePen(PS_SOLID,3,RGB(192,192,192));
CPen *pSpen = pDC->SelectObject(&spen);
pDC->SelectObject(GetStockObject(NULL_BRUSH));//选择透明填充
pDC->Rectangle(0,0,rect.Width()-3,rect.Height()-3);
pDC->SelectObject(pSpen);
DeleteObject(spen);//释放资源
ReleaseDC(pDC);
//////////////////////////////////////////////////
C# 获取桌面
[System.Runtime.InteropServices.DllImport(”gdi32.dll”)] public static extern int BitBlt(IntPtr hdcDest, int nXDest, int nYDest, int nWidth, int nHeight, IntPtr hdcSrc, int nXSrc, int nYSrc, UInt32 dwRop); //创建桌面句柄 [System.Runtime.InteropServices.DllImportAttribute(”gdi32.dll”)] public static extern IntPtr CreateDC(string lpszDriver, string lpszDevice, string lpszOutput, int lpInitData); [System.Runtime.InteropServices.DllImport(”gdi32.dll”)] public static extern IntPtr CreateCompatibleDC(IntPtr hdc); //转换为本地的图像资源 [System.Runtime.InteropServices.DllImport(”gdi32.dll”)] public static extern IntPtr CreateCompatibleBitmap(IntPtr hdc, int nWidth, int nHeight); [System.Runtime.InteropServices.DllImport(”gdi32.dll”)] public static extern IntPtr SelectObject(IntPtr hdc, IntPtr hgdiobj); [System.Runtime.InteropServices.DllImport(”gdi32.dll”)] public static extern int DeleteDC(IntPtr hdc); //释放用过的设备句柄 [DllImport(”user32.dll”)] public static extern bool ReleaseDC( IntPtr hwnd, IntPtr hdc ); //释放用过的画笔等资源 [DllImport(”gdi32.dll”)] public static extern bool DeleteObject( IntPtr hdc ); /// <summary> /// 截取屏幕图像 /// </summary> /// <param name=”Width”>宽</param> /// <param name=”Height”>高</param> /// <param name=”x”>x坐标(全屏时候为0)</param> /// <param name=”y”>y坐标(全屏时候为0)</param> /// <returns></returns> public Bitmap fullphoto(int Width,int Height,int x,int y) { Bitmap bitmap; //try //{ IntPtr hScreenDc = CreateDC(”DISPLAY”, null, null, 0); // 创建桌面句柄 IntPtr hMemDc = CreateCompatibleDC(hScreenDc); // 创建与桌面句柄相关连的内存DC IntPtr hBitmap = CreateCompatibleBitmap(hScreenDc, Width, Height); IntPtr hOldBitmap = SelectObject(hMemDc, hBitmap); BitBlt(hMemDc, x, y, Width, Height, hScreenDc, x, y, (UInt32)0xcc0020); IntPtr map = SelectObject(hMemDc, hOldBitmap); bitmap = Bitmap.FromHbitmap(map); ReleaseDC(hBitmap, hScreenDc); DeleteDC(hScreenDc);//删除用过的对象 DeleteDC(hMemDc);//删除用过的对象 DeleteDC(hOldBitmap); DeleteObject(hBitmap); //} //catch (Exception wx) //{ // return null; //} // number= number +1; // bitmap.Save(”screen” + number + “.bmp”); return bitmap; }
C#用API实现指定颜色填充一个闭合区域
C#用API实现指定颜色填充一个闭合区域
C#用API实现指定颜色填充一个闭合区域代码如下:
using System.Runtime.InteropServices; [DllImport("gdi32.dll")] public static extern IntPtr SelectObject(IntPtr hdc, IntPtr hgdiobj); [DllImport("gdi32.dll")] public static extern IntPtr CreateSolidBrush(int crColor); [DllImport("gdi32.dll")] public static extern bool ExtFloodFill(IntPtr hdc, int nXStart, int nYStart, int crColor, uint fuFillType); [DllImport("gdi32.dll")] public static extern bool DeleteObject(IntPtr hObject); [DllImport("gdi32.dll")] public static extern int GetPixel(IntPtr hdc, int x, int y); public static uint FLOODFILLBORDER = 0; public static uint FLOODFILLSURFACE = 1; private void button1_Click(object sender, EventArgs e) { Graphics vGraphics = Graphics.FromHwnd(Handle); vGraphics.DrawRectangle(Pens.Blue, new Rectangle(0, 0, 300, 300)); vGraphics.DrawRectangle(Pens.Blue, new Rectangle(50, 70, 300, 300)); IntPtr vDC = vGraphics.GetHdc(); IntPtr vBrush = CreateSolidBrush(ColorTranslator.ToWin32(Color.Red)); IntPtr vPreviouseBrush = SelectObject(vDC, vBrush); ExtFloodFill(vDC, 10, 10, GetPixel(vDC, 10, 10), FLOODFILLSURFACE); SelectObject(vDC, vPreviouseBrush); DeleteObject(vBrush); vGraphics.ReleaseHdc(vDC); }WinCE平台下C#引用API(GDI)一个值得警惕的内存泄漏由于C#精简框架集绘图函数不支持圆角矩形,所以引用了相关的API。
[DllImport("//windows//coredll.dll", EntryPoint = "RoundRect")] private static extern int CeRoundRect(IntPtr hdc, int X1, int Y1, int X2, int Y2, int X3, int Y3);
这是有内存泄漏的源码:
public static int RoundRect(Graphics e, Pen pen, SolidBrush brush, int X1, int Y1, int X2, int Y2, int X3, int Y3) { IntPtr hpen; IntPtr hbrush;
if(pen!=null) { hpen = CreatePen((DashStyle.Solid == pen.DashStyle) ? 0 : 1, (int)pen.Width, SetRGB(pen.Color.R, pen.Color.G, pen.Color.B)); //创建GDI画笔 } else { hpen = GetStockObject(8); //空画笔 }
if (brush!= null) { hbrush = CreateSolidBrush(SetRGB(brush.Color.R, brush.Color.G, brush.Color.B)); //brush.Color.ToArgb()); } else { hbrush = GetStockObject(5); }
//pen.Dispose(); //brush.Dispose();
IntPtr hdc = e.GetHdc(); //--------------------- SelectObject(hdc, hbrush); SelectObject(hdc, hpen); int intRet=RoundRect(hdc, X1, Y1, X2,Y2, X3, Y3);
DeleteObject(hbrush); DeleteObject(hpen); //--------------------- e.ReleaseHdc(hdc); return intRet; }
这是没有问题的源码:
public static int RoundRect(Graphics e, Pen pen, SolidBrush brush, int X1, int Y1, int X2, int Y2, int X3, int Y3) { IntPtr hpen,old_pen; IntPtr hbrush, old_brush;
if(pen!=null) { hpen = CreatePen((DashStyle.Solid == pen.DashStyle) ? 0 : 1, (int)pen.Width, SetRGB(pen.Color.R, pen.Color.G, pen.Color.B)); //创建GDI画笔 } else { hpen = GetStockObject(8); //空画笔 }
if (brush!= null) { hbrush = CreateSolidBrush(SetRGB(brush.Color.R, brush.Color.G, brush.Color.B)); //brush.Color.ToArgb()); } else { hbrush = GetStockObject(5); }
//pen.Dispose(); //brush.Dispose();
IntPtr hdc = e.GetHdc(); //--------------------- old_brush=SelectObject(hdc, hbrush); old_pen=SelectObject(hdc, hpen); int intRet=RoundRect(hdc, X1, Y1, X2,Y2, X3, Y3);
SelectObject(hdc, old_brush); SelectObject(hdc, old_pen); DeleteObject(hbrush); DeleteObject(hpen); //--------------------- e.ReleaseHdc(hdc); return intRet; }
看出代码的区别来了没有?泄漏的原因其实很简单,就是没有重新选入旧的画笔画刷。同样的程序(当然PC端的API库是GDI32)在上位机Window XP平台上没有什么问题(测试大约3天以上),而在WinCE平台确非常明显,大约1~3个小时(视圆角矩形绘图的多寡而定),该程序就会内存耗尽而死。