C#调用win32API画图函数示例

旧城等待， 2022-05-20 01:41 460阅读 0赞

## 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][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。

[http_blog.csdn.net_caimouse_archive_2007_09_05_1773850.aspx]: http://blog.csdn.net/caimouse/archive/2007/09/05/1773850.aspx