C++编程逻辑讲解step by step：多态

概念

 C++面向对象中的多态性是指同一种类型的对象在不同的情况下表现出不同的行为。

从代码层面看，实际上“同一种类型”就表明了，这里可以在循环里用相同的代码统一处理不同的功能。这一点很重要。

题目

界面上，拖动鼠标画矩形或者椭圆。

分析

先定义出矩形CShpRectangle和椭圆类CShpEllipse。因为要实现多态，还要先声明一个基类CShape，基类里有一个绘图功能Draw()，而且还得说明成虚函数，就是打算要。

这里用VC++代码，CObject是所有类的祖宗，所以都得从CObject继承过来“表现出不同的行为”。

class CShape : public CObject  
{
public:

....

    virtual void Draw(CDC* pDC) 
                     { TRACE("My Error: In CShape::Draw.\n");
                         ASSERT(FALSE); };

};

class CShpRectangle : public CShape
{
public:
    void Draw(CDC* pDC);    // Overrides CShape::Draw
};

class CShpEllipse : public CShape
{
public:

    void Draw(CDC* pDC); 

};

定义"不同的行为"：

CShape中的Draw()是虚的，所以没功能可定义；

void CShpRectangle::Draw(CDC* pDC)  // Virtual override
{
    pDC->Rectangle(m_boxShape);//根据m_boxShape给的坐标开始画图
}

void CShpEllipse::Draw(CDC* pDC)  // Virtual override
{
    pDC->Ellipse(m_boxShape);
}

处理"不同的行为"：

先定义一个基类指针   CShape* pShape; 再让这个指针指向它派生类的对象，这里实际有个强制类型转换，不然基类和派生类毕竟不是同一个类型，经过转换就是同一个类型了。

void CMyDrawView::OnDraw(CDC* pDC)
{......

    CShape* pShape;
    pDoc->SetToOldestShape();
    while(pDoc->GetPos() != NULL)
    {
        pShape = pDoc->GetPrevShape();//GetPrevShape()函数就是做了一个强制转换(CShape*)，先不用关注细节
        pShape->Draw(pDC);
    }

}

至此，多态的结构就结束了。其他代码都是各种附加功能：设置画笔风格、画矩形还是椭圆的切换、画的效果等等。

// Shape.h: interface for the CShape class.
//
//#if !defined(AFX_SHAPE_H__97288485_7254_11D2_991B_00C04FC29F5C__INCLUDED_)
#define AFX_SHAPE_H__97288485_7254_11D2_991B_00C04FC29F5C__INCLUDED_#if _MSC_VER > 1000
#pragma once
#endif // _MSC_VER > 1000enum ShpType
{shpRectangle,shpEllipse
};class CShape : public CObject  
{
public:// Enable MFC serialization (file storage for class objects)DECLARE_SERIAL(CShape)// Constructors and operators// Default constructor CShape();// Copy constructorCShape(const CShape& s){m_boxShape = s.m_boxShape;m_bTransparent = s.m_bTransparent;m_nColorShape = s.m_nColorShape;}// Overloaded assignment operatorCShape& operator=(const CShape& s){m_boxShape = s.m_boxShape;m_bTransparent = s.m_bTransparent;m_nColorShape = s.m_nColorShape;return *this;}// Attributes - deliberately left public for easy access// Note: no longer need an m_typeShape member.CRect m_boxShape;bool m_bTransparent;UINT m_nColorShape;// Overridables and operationsvirtual void Draw(CDC* pDC) { TRACE("My Error: In CShape::Draw.\n");ASSERT(FALSE); };// Implementation
public:virtual ~CShape();};// Concrete subclass of abstract base class CShape
class CShpRectangle : public CShape
{
public:DECLARE_SERIAL(CShpRectangle)// Constructors are inherited from CShape.// Attributes inherited include://  m_boxShape, m_bTransparent, m_nColorShape// Operationsvoid Draw(CDC* pDC);    // Overrides CShape::Draw// Implementation
public:
};// Concrete subclass of abstract base class CShape
class CShpEllipse : public CShape
{
public:DECLARE_SERIAL(CShpEllipse)// Constructors are inherited from CShape.// Attributes inherited include: //  m_boxShape, m_bTransparent, m_nColorShape// Operationsvoid Draw(CDC* pDC);    // Overrides CShape::Draw// Implementation
public:
};#endif // !defined(AFX_SHAPE_H__97288485_7254_11D2_991B_00C04FC29F5C__INCLUDED_)// DrawVw.h : interface of the CMyDrawView class
//
/#if !defined(AFX_DRAWVW_H__24958326_5D0A_11D2_991B_00C04FC29F5C__INCLUDED_)
#define AFX_DRAWVW_H__24958326_5D0A_11D2_991B_00C04FC29F5C__INCLUDED_#if _MSC_VER > 1000
#pragma once
#endif // _MSC_VER > 1000#include "DrawDoc.h"// Array of actual colors, indexed
//  by CMyDrawView::m_nColorNext
static COLORREF arColors[10] =  
{RGB(0,0,0),         // BlackRGB(0,0,255),       // BlueRGB(0,255,0),       // GreenRGB(0,255,255),     // CyanRGB(255,0,0),       // RedRGB(255,0,255),     // MagentaRGB(255,255,0),     // YellowRGB(255,255,255),   // WhiteRGB(128,128,128),   // Dark grayRGB(192,192,192)    // Light gray
};class CMyDrawView : public CView
{
protected: // create from serialization onlyCMyDrawView();DECLARE_DYNCREATE(CMyDrawView)// Attributes
public:CMyDrawDoc* GetDocument();ShpType m_typeNext;       // Type of CShape to draw nextCShape* m_pShpTemp;       // The current CShape being drawnbool m_bCaptured;         // True if mouse has been capturedCBrush* m_pBrushOld;      // Store brush for interior of shapesbool m_bTransparent;      // True if Transparent selectedUINT m_nColorNext;        // Store ID for color to simplify // updating menusCPen* m_pPenOld;          // Pen for drawing CShape outlinesCPen* m_pPenNew;          // Store pens we create// Operations
public:// Overrides// ClassWizard generated virtual function overrides//{{AFX_VIRTUAL(CMyDrawView)public:virtual void OnDraw(CDC* pDC);  // overridden to draw this viewvirtual BOOL PreCreateWindow(CREATESTRUCT& cs);protected:virtual BOOL OnPreparePrinting(CPrintInfo* pInfo);virtual void OnBeginPrinting(CDC* pDC, CPrintInfo* pInfo);virtual void OnEndPrinting(CDC* pDC, CPrintInfo* pInfo);//}}AFX_VIRTUAL// Implementation
public:void InvertShape(CDC *pDC, CShape &s, bool bInvert = true);void ResetPenBrush(CDC * pDC);void SetPenBrush(CDC * pDC, bool bTransparent, UINT nColor);virtual ~CMyDrawView();
#ifdef _DEBUGvirtual void AssertValid() const;virtual void Dump(CDumpContext& dc) const;
#endifprotected:// Generated message map functions
protected://{{AFX_MSG(CMyDrawView)afx_msg void OnToolRectangle();afx_msg void OnToolEllipse();afx_msg void OnLButtonDown(UINT nFlags, CPoint point);afx_msg void OnMouseMove(UINT nFlags, CPoint point);afx_msg void OnLButtonUp(UINT nFlags, CPoint point);afx_msg void OnUpdateToolRectangle(CCmdUI* pCmdUI);afx_msg void OnUpdateToolEllipse(CCmdUI* pCmdUI);afx_msg void OnToolTransparent();afx_msg void OnUpdateToolTransparent(CCmdUI* pCmdUI);//}}AFX_MSGafx_msg void OnToolColor(UINT nID);  // ON_COMMAND_RANGE handlerafx_msg void OnUpdateToolColor(CCmdUI* pCmdUI);DECLARE_MESSAGE_MAP()
};#ifndef _DEBUG  // debug version in DrawVw.cpp
inline CMyDrawDoc* CMyDrawView::GetDocument(){ return (CMyDrawDoc*)m_pDocument; }
#endif///{{AFX_INSERT_LOCATION}}
// Microsoft Visual C++ will insert additional declarations immediately before the previous line.#endif // !defined(AFX_DRAWVW_H__24958326_5D0A_11D2_991B_00C04FC29F5C__INCLUDED_)// DrawDoc.h : interface of the CMyDrawDoc class
//
/#if !defined(AFX_DRAWDOC_H__24958324_5D0A_11D2_991B_00C04FC29F5C__INCLUDED_)
#define AFX_DRAWDOC_H__24958324_5D0A_11D2_991B_00C04FC29F5C__INCLUDED_#if _MSC_VER > 1000
#pragma once
#endif // _MSC_VER > 1000#include "Shape.h"class CMyDrawDoc : public CDocument
{
protected: // create from serialization onlyCMyDrawDoc();DECLARE_DYNCREATE(CMyDrawDoc)// Attributes
public:void SetToOldestShape() { m_pos = m_listShapes.GetTailPosition(); };void SetToLatestShape() { m_pos = m_listShapes.GetHeadPosition(); };CShape* GetPrevShape(){// Sets m_pos to NULL if no shapes or if//  latest shape is last in list.return (CShape*)m_listShapes.GetPrev(m_pos);};CShape* GetNextShape(){// Sets m_pos to NULL if no shapes or if//  latest shape is last in listreturn (CShape*)m_listShapes.GetNext(m_pos);};POSITION GetPos() const{// m_pos tells you where you are in a list of the shapes.// Use GetPos with either iteration direction to test for end.return m_pos;   // Can be NULL};int GetCount() const{// Return the number of stored shapes.return m_listShapes.GetCount();};private:CObList m_listShapes;  // Linked list of all shapes drawn so farPOSITION m_pos;        // Latest position accessed// Operations
public:// Overrides// ClassWizard generated virtual function overrides//{{AFX_VIRTUAL(CMyDrawDoc)public:virtual BOOL OnNewDocument();virtual void Serialize(CArchive& ar);virtual void DeleteContents();//}}AFX_VIRTUAL// Implementation
public:CShape* CreateShape(ShpType st);void DeleteAllShapes();void DeleteLatestShape();virtual ~CMyDrawDoc();
#ifdef _DEBUGvirtual void AssertValid() const;virtual void Dump(CDumpContext& dc) const;
#endifprotected:// Generated message map functions
protected://{{AFX_MSG(CMyDrawDoc)// NOTE - the ClassWizard will add and remove member functions here.//    DO NOT EDIT what you see in these blocks of generated code !//}}AFX_MSGDECLARE_MESSAGE_MAP()
};///{{AFX_INSERT_LOCATION}}
// Microsoft Visual C++ will insert additional declarations immediately before the previous line.#endif // !defined(AFX_DRAWDOC_H__24958324_5D0A_11D2_991B_00C04FC29F5C__INCLUDED_)// DrawDoc.cpp : implementation of the CMyDrawDoc class
//#include "stdafx.h"
#include "MyDraw.h"#include "DrawDoc.h"#ifdef _DEBUG
#define new DEBUG_NEW
#undef THIS_FILE
static char THIS_FILE[] = __FILE__;
#endif/
// CMyDrawDocIMPLEMENT_DYNCREATE(CMyDrawDoc, CDocument)BEGIN_MESSAGE_MAP(CMyDrawDoc, CDocument)//{{AFX_MSG_MAP(CMyDrawDoc)// NOTE - the ClassWizard will add and remove mapping macros here.//    DO NOT EDIT what you see in these blocks of generated code!//}}AFX_MSG_MAP
END_MESSAGE_MAP()/
// CMyDrawDoc construction/destructionCMyDrawDoc::CMyDrawDoc()
{// TODO: add one-time construction code herem_pos = NULL;
}CMyDrawDoc::~CMyDrawDoc()
{
}BOOL CMyDrawDoc::OnNewDocument()
{if (!CDocument::OnNewDocument())return FALSE;// TODO: add reinitialization code here// (SDI documents will reuse this document)return TRUE;
}/
// CMyDrawDoc serializationvoid CMyDrawDoc::Serialize(CArchive& ar)
{if (ar.IsStoring()){// TODO: add storing code here}else{// TODO: add loading code here}
}/
// CMyDrawDoc diagnostics#ifdef _DEBUG
void CMyDrawDoc::AssertValid() const
{CDocument::AssertValid();
}void CMyDrawDoc::Dump(CDumpContext& dc) const
{CDocument::Dump(dc);
}
#endif //_DEBUG/
// CMyDrawDoc commandsvoid CMyDrawDoc::DeleteLatestShape()
{ASSERT(!m_listShapes.IsEmpty());CShape* pShape = (CShape*)m_listShapes.RemoveHead();delete pShape;
}void CMyDrawDoc::DeleteAllShapes()
{POSITION pos = m_listShapes.GetHeadPosition(); // NULL if emptywhile(pos != NULL){delete m_listShapes.GetNext(pos);}m_listShapes.RemoveAll();SetModifiedFlag(false); // Nothing to save now
}void CMyDrawDoc::DeleteContents() 
{// TODO: Add your specialized code here and/or call the base classDeleteAllShapes();UpdateAllViews(NULL);CDocument::DeleteContents();
}CShape* CMyDrawDoc::CreateShape(ShpType st)
{ASSERT(st >= shpRectangle && st <= shpEllipse);switch(st){case shpRectangle:{CShpRectangle* pRectangle = new CShpRectangle;ASSERT(pRectangle != NULL);m_listShapes.AddHead(pRectangle);}break;case shpEllipse:{CShpEllipse* pEllipse = new CShpEllipse;ASSERT(pEllipse != NULL);m_listShapes.AddHead(pEllipse);}break;default: ;  // Nothing}// Return the object just created.if(m_listShapes.GetCount() > 0)         return (CShape*)m_listShapes.GetHead();     elsereturn NULL;}// MyDraw.cpp : Defines the class behaviors for the application.
//#include "stdafx.h"
#include "MainFrm.h"#include "MyDraw.h"
#include "DrawVw.h"#ifdef _DEBUG
#define new DEBUG_NEW
#undef THIS_FILE
static char THIS_FILE[] = __FILE__;
#endif/
// CMyDrawAppBEGIN_MESSAGE_MAP(CMyDrawApp, CWinApp)//{{AFX_MSG_MAP(CMyDrawApp)ON_COMMAND(ID_APP_ABOUT, OnAppAbout)// NOTE - the ClassWizard will add and remove mapping macros here.//    DO NOT EDIT what you see in these blocks of generated code!//}}AFX_MSG_MAP// Standard file based document commandsON_COMMAND(ID_FILE_NEW, CWinApp::OnFileNew)ON_COMMAND(ID_FILE_OPEN, CWinApp::OnFileOpen)// Standard print setup commandON_COMMAND(ID_FILE_PRINT_SETUP, CWinApp::OnFilePrintSetup)
END_MESSAGE_MAP()/
// CMyDrawApp constructionCMyDrawApp::CMyDrawApp()
{// TODO: add construction code here,// Place all significant initialization in InitInstance
}/
// The one and only CMyDrawApp objectCMyDrawApp theApp;/
// CMyDrawApp initializationBOOL CMyDrawApp::InitInstance()
{// Standard initialization// If you are not using these features and wish to reduce the size//  of your final executable, you should remove from the following//  the specific initialization routines you do not need.#ifdef _AFXDLLEnable3dControls();			// Call this when using MFC in a shared DLL
#elseEnable3dControlsStatic();	// Call this when linking to MFC statically
#endif// Change the registry key under which our settings are stored.// TODO: You should modify this string to be something appropriate// such as the name of your company or organization.SetRegistryKey(_T("Local AppWizard-Generated Applications"));LoadStdProfileSettings();  // Load standard INI file options (including MRU)// Register the application's document templates.  Document templates//  serve as the connection between documents, frame windows and views.CSingleDocTemplate* pDocTemplate;pDocTemplate = new CSingleDocTemplate(IDR_MAINFRAME,RUNTIME_CLASS(CMyDrawDoc),RUNTIME_CLASS(CMainFrame),       // main SDI frame windowRUNTIME_CLASS(CMyDrawView));AddDocTemplate(pDocTemplate);// Enable DDE Execute openEnableShellOpen();RegisterShellFileTypes(TRUE);// Parse command line for standard shell commands, DDE, file openCCommandLineInfo cmdInfo;ParseCommandLine(cmdInfo);// Dispatch commands specified on the command lineif (!ProcessShellCommand(cmdInfo))return FALSE;// The one and only window has been initialized, so show and update it.m_pMainWnd->ShowWindow(SW_SHOW);m_pMainWnd->UpdateWindow();// Enable drag/drop openm_pMainWnd->DragAcceptFiles();return TRUE;
}/
// CAboutDlg dialog used for App Aboutclass CAboutDlg : public CDialog
{
public:CAboutDlg();// Dialog Data//{{AFX_DATA(CAboutDlg)enum { IDD = IDD_ABOUTBOX };//}}AFX_DATA// ClassWizard generated virtual function overrides//{{AFX_VIRTUAL(CAboutDlg)protected:virtual void DoDataExchange(CDataExchange* pDX);    // DDX/DDV support//}}AFX_VIRTUAL// Implementation
protected://{{AFX_MSG(CAboutDlg)// No message handlers//}}AFX_MSGDECLARE_MESSAGE_MAP()
};CAboutDlg::CAboutDlg() : CDialog(CAboutDlg::IDD)
{//{{AFX_DATA_INIT(CAboutDlg)//}}AFX_DATA_INIT
}void CAboutDlg::DoDataExchange(CDataExchange* pDX)
{CDialog::DoDataExchange(pDX);//{{AFX_DATA_MAP(CAboutDlg)//}}AFX_DATA_MAP
}BEGIN_MESSAGE_MAP(CAboutDlg, CDialog)//{{AFX_MSG_MAP(CAboutDlg)// No message handlers//}}AFX_MSG_MAP
END_MESSAGE_MAP()// App command to run the dialog
void CMyDrawApp::OnAppAbout()
{CAboutDlg aboutDlg;aboutDlg.DoModal();
}/
// CMyDrawApp message handlers
// Shape.cpp: implementation of the CShape class.
//
//#include "stdafx.h"
#include "MyDraw.h"
#include "Shape.h"
#include "Resource.h"#ifdef _DEBUG
#undef THIS_FILE
static char THIS_FILE[]=__FILE__;
#define new DEBUG_NEW
#endif//
// Construction/Destruction
//// Class CShape implementationIMPLEMENT_SERIAL(CShape, CObject, 1)CShape::CShape()
{m_boxShape.SetRect(0, 0, 0, 0);m_bTransparent = true;m_nColorShape = ID_COLOR_BLACK;
}CShape::~CShape()
{}// Class CShpRectangle implementationIMPLEMENT_SERIAL(CShpRectangle, CShape, 1)void CShpRectangle::Draw(CDC* pDC)  // Virtual override
{pDC->Rectangle(m_boxShape);
}// Class CShpEllipse implementationIMPLEMENT_SERIAL(CShpEllipse, CShape, 1)void CShpEllipse::Draw(CDC* pDC)  // Virtual override
{pDC->Ellipse(m_boxShape);
}
// DrawVw.cpp : implementation of the CMyDrawView class
//#include "stdafx.h"#include "MyDraw.h"
#include "DrawVw.h"#ifdef _DEBUG
#define new DEBUG_NEW
#undef THIS_FILE
static char THIS_FILE[] = __FILE__;
#endif/
// CMyDrawViewIMPLEMENT_DYNCREATE(CMyDrawView, CView)BEGIN_MESSAGE_MAP(CMyDrawView, CView)//{{AFX_MSG_MAP(CMyDrawView)ON_COMMAND(ID_TOOL_RECTANGLE, OnToolRectangle)ON_COMMAND(ID_TOOL_ELLIPSE, OnToolEllipse)ON_WM_LBUTTONDOWN()ON_WM_MOUSEMOVE()ON_WM_LBUTTONUP()ON_UPDATE_COMMAND_UI(ID_TOOL_RECTANGLE, OnUpdateToolRectangle)ON_UPDATE_COMMAND_UI(ID_TOOL_ELLIPSE, OnUpdateToolEllipse)ON_COMMAND(ID_TOOL_TRANSPARENT, OnToolTransparent)ON_UPDATE_COMMAND_UI(ID_TOOL_TRANSPARENT, OnUpdateToolTransparent)//}}AFX_MSG_MAP// Standard printing commandsON_COMMAND(ID_FILE_PRINT, CView::OnFilePrint)ON_COMMAND(ID_FILE_PRINT_DIRECT, CView::OnFilePrint)ON_COMMAND(ID_FILE_PRINT_PREVIEW, CView::OnFilePrintPreview)ON_COMMAND_RANGE(ID_COLOR_BLACK, ID_COLOR_LTGRAY, OnToolColor)ON_UPDATE_COMMAND_UI_RANGE(ID_COLOR_BLACK, ID_COLOR_LTGRAY, OnUpdateToolColor)
END_MESSAGE_MAP()/
// CMyDrawView construction/destructionCMyDrawView::CMyDrawView()
{// TODO: add construction code here// Initialize random number generator for random bounding rects.m_typeNext = shpRectangle;m_bCaptured = false;m_pBrushOld = NULL;m_bTransparent = true;m_nColorNext = ID_COLOR_BLACK;m_pPenOld = NULL;m_pPenNew = NULL;}CMyDrawView::~CMyDrawView()
{
}BOOL CMyDrawView::PreCreateWindow(CREATESTRUCT& cs)
{// TODO: Modify the Window class or styles here by modifying//  the CREATESTRUCT csreturn CView::PreCreateWindow(cs);
}/
// CMyDrawView drawingvoid CMyDrawView::OnDraw(CDC* pDC)
{CMyDrawDoc* pDoc = GetDocument();ASSERT_VALID(pDoc);// TODO: add draw code for native data here// Iterate the shapes from oldest to newest.// (Draw them in the same order as originally drawn).CShape* pShape;pDoc->SetToOldestShape();while(pDoc->GetPos() != NULL){// Get the shape and use it to set the pen and brush.// Last shape sets position to NULL.pShape = pDoc->GetPrevShape();SetPenBrush(pDC, pShape->m_bTransparent, pShape->m_nColorShape);// Ask the shape to draw itself.pShape->Draw(pDC);// Clean up.ResetPenBrush(pDC);}}/
// CMyDrawView printingBOOL CMyDrawView::OnPreparePrinting(CPrintInfo* pInfo)
{// default preparationreturn DoPreparePrinting(pInfo);
}void CMyDrawView::OnBeginPrinting(CDC* /*pDC*/, CPrintInfo* /*pInfo*/)
{// TODO: add extra initialization before printing
}void CMyDrawView::OnEndPrinting(CDC* /*pDC*/, CPrintInfo* /*pInfo*/)
{// TODO: add cleanup after printing
}/
// CMyDrawView diagnostics#ifdef _DEBUG
void CMyDrawView::AssertValid() const
{CView::AssertValid();
}void CMyDrawView::Dump(CDumpContext& dc) const
{CView::Dump(dc);
}CMyDrawDoc* CMyDrawView::GetDocument() // non-debug version is inline
{ASSERT(m_pDocument->IsKindOf(RUNTIME_CLASS(CMyDrawDoc)));return (CMyDrawDoc*)m_pDocument;
}
#endif //_DEBUG/
// CMyDrawView message handlersvoid CMyDrawView::OnToolRectangle() 
{// TODO: Add your command handler code herem_typeNext = shpRectangle;
}void CMyDrawView::OnToolEllipse() 
{// TODO: Add your command handler code herem_typeNext = shpEllipse;    
}// Generate a random positive coordinate within a COORD_MAX- 
//  by COORD_MAX-unit drawing area.void CMyDrawView::OnLButtonDown(UINT nFlags, CPoint point) 
{// TODO: Add your message handler code here and/or call defaultSetCapture();m_bCaptured = true;ASSERT(m_typeNext == shpRectangle || m_typeNext == shpEllipse);CMyDrawDoc* pDoc = GetDocument();ASSERT_VALID(pDoc);// Create CShape and add it to our list; return a ptr to it.m_pShpTemp = pDoc->CreateShape(m_typeNext);// Mark the document as changed.pDoc->SetModifiedFlag();// Start setting properties of the new shape.m_pShpTemp->m_bTransparent = m_bTransparent;m_pShpTemp->m_nColorShape = m_nColorNext;// Store starting point - literally a point, initially //  (topLeft == botRight).m_pShpTemp->m_boxShape.left = m_pShpTemp->m_boxShape.right = point.x;m_pShpTemp->m_boxShape.top = m_pShpTemp->m_boxShape.bottom = point.y;CView::OnLButtonDown(nFlags, point);  }void CMyDrawView::OnMouseMove(UINT nFlags, CPoint point) 
{// TODO: Add your message handler code here and/or call defaultif(m_bCaptured){CClientDC dc(this);// Erase previous rectangle first.InvertShape(&dc, *m_pShpTemp);// Store new temporary corner as bottom right.m_pShpTemp->m_boxShape.bottom = point.y;m_pShpTemp->m_boxShape.right = point.x;// Draw new rectangle (latest rubberbanded rectangle).InvertShape(&dc, *m_pShpTemp);}CView::OnMouseMove(nFlags, point);
}void CMyDrawView::OnLButtonUp(UINT nFlags, CPoint point) 
{// TODO: Add your message handler code here and/or call default
if(m_bCaptured){::ReleaseCapture();m_bCaptured = false;CClientDC dc(this);// Erase previous rubberband rectangle.InvertShape(&dc, *m_pShpTemp);// Set the botRight corner's final values.m_pShpTemp->m_boxShape.right = point.x;m_pShpTemp->m_boxShape.bottom = point.y;// Draw final rectangle.InvertShape(&dc, *m_pShpTemp, false);  // Draw}CView::OnLButtonUp(nFlags, point);
}void CMyDrawView::SetPenBrush(CDC *pDC, bool bTransparent, UINT nColor)
{ASSERT(pDC != NULL);// Make CShape's interior empty (transparent).if(bTransparent){m_pBrushOld = (CBrush*)pDC->SelectStockObject(NULL_BRUSH);}else{m_pBrushOld = (CBrush*)pDC->SelectStockObject(WHITE_BRUSH);}ASSERT(m_pBrushOld != NULL);// Set up the penASSERT(nColor - ID_COLOR_BLACK >= 0 &&nColor - ID_COLOR_BLACK <= (sizeof(arColors) / sizeof(arColors[0])));// Construct pen object on heap so we can clean it up after usem_pPenNew = new CPen();// Create the GDI pen & select it into the device context.m_pPenNew->CreatePen(PS_INSIDEFRAME, 0, arColors[nColor - ID_COLOR_BLACK]);m_pPenOld = (CPen*)pDC->SelectObject(m_pPenNew);// Device context restored in companion function //  ResetPenBrush}void CMyDrawView::ResetPenBrush(CDC *pDC)
{ASSERT(pDC != NULL);// Restore previous pen and brush to device context after use.ASSERT(m_pBrushOld != NULL);pDC->SelectObject(m_pBrushOld);pDC->SelectObject(m_pPenOld);// Our responsibility to delete the heap objectdelete m_pPenNew;m_pPenNew = NULL;m_pPenOld = NULL;m_pBrushOld = NULL;
}void CMyDrawView::InvertShape(CDC *pDC, CShape &s, bool bInvert)
{ASSERT(pDC != NULL);// Drawing mode is R2_NOT: black -> white, white -> black,//  colors -> inverse color.// If CShape already drawn, this erases; else draws it.int nModeOld;if(bInvert){nModeOld = pDC->SetROP2(R2_NOT);}// Draw the CShape (or erase it).SetPenBrush(pDC, s.m_bTransparent, s.m_nColorShape);s.Draw(pDC);// Restore old values in DC.if(bInvert){pDC->SetROP2(nModeOld);}ResetPenBrush(pDC);}void CMyDrawView::OnUpdateToolRectangle(CCmdUI* pCmdUI) 
{// TODO: Add your command update UI handler code herepCmdUI->SetCheck(m_typeNext == shpRectangle);   
}void CMyDrawView::OnUpdateToolEllipse(CCmdUI* pCmdUI) 
{// TODO: Add your command update UI handler code herepCmdUI->SetCheck(m_typeNext == shpEllipse); 
}void CMyDrawView::OnToolTransparent() 
{// TODO: Add your command handler code herem_bTransparent = !m_bTransparent;
}void CMyDrawView::OnUpdateToolTransparent(CCmdUI* pCmdUI) 
{// TODO: Add your command update UI handler code herepCmdUI->SetCheck(m_bTransparent);
}void CMyDrawView::OnToolColor(UINT nID)
{// Set the color for future CShape drawingm_nColorNext = nID;
}void CMyDrawView::OnUpdateToolColor(CCmdUI* pCmdUI)
{// Check or uncheck all color menu items// Check item if it's the currently selected color// Uncheck all other colorspCmdUI->SetCheck(pCmdUI->m_nID == m_nColorNext);
}

本文来自互联网用户投稿，该文观点仅代表作者本人，不代表本站立场。本站仅提供信息存储空间服务，不拥有所有权，不承担相关法律责任。如若转载，请注明出处：http://www.mzph.cn/bicheng/40127.shtml

如若内容造成侵权/违法违规/事实不符，请联系多彩编程网进行投诉反馈email:809451989@qq.com，一经查实，立即删除！

相关文章

自动做市商AMM

自动做市商AMM

自动做市商&#xff08;AMM&#xff09;&#xff1a;重塑去中心化金融的市场机制 1、为什么需要AMM&#xff1f; 在传统金融市场中&#xff0c;做市商通过提供买卖双方的报价来维持市场的流动性和稳定性。然而&#xff0c;在去中心化金融&#xff08;DeFi&#xff09;领域&am…
阅读更多...
linux screen

linux screen

计算机最开始只有黑白界面,我们通过键盘设备输入字符进行编程等行为进行编程, 让计算机完成我们设定的任务. 随着计算机技术及硬件的发展, 黑白屏幕被图形界面替代, 应用程序的 GUI 界面操作成为主流, 只有远程终端由于带宽占用少,实时性高等优点一直存在到现在. 然后有时由于网…
阅读更多...
FFmpeg开发笔记（四十三）使用SRS开启SRT协议的视频直播服务

FFmpeg开发笔记（四十三）使用SRS开启SRT协议的视频直播服务

《FFmpeg开发实战&#xff1a;从零基础到短视频上线》一书在第10章介绍了轻量级流媒体服务器MediaMTX&#xff0c;通过该工具可以测试RTSP/RTMP等流媒体协议的推拉流。不过MediaMTX的功能实在是太简单了&#xff0c;无法应用于真实直播的生产环境&#xff0c;真正能用于生产环境…
阅读更多...
java项目总结2

java项目总结2

3.了解Java的内存分配 4.重载 定义&#xff1a;在一个类中&#xff0c;有相同名的&#xff0c;但是却是不同参数&#xff08;返回类型可以不一样&#xff09; 重载的优点&#xff1a; 1.减少定义方法时使用的单词 2.减少调用方法时候的麻烦&#xff08;比如sum的返回两个数的…
阅读更多...
AUTOSAR汽车电子嵌入式编程精讲300篇-智能网联汽车CAN总线-基于迁移学习的驾驶行为评价方法

AUTOSAR汽车电子嵌入式编程精讲300篇-智能网联汽车CAN总线-基于迁移学习的驾驶行为评价方法

目录 前言 驾驶行为评价相关研究 系统模型和应用价值 挑战和解决方案 迁移学习在汽车工业中的应用 算法模型 驾驶行为评价模型的设计 驾驶行为数据的收集和预处理 驾驶行为评价模型的搭建 实验环境和数值结果 实验环境 MTL网络性能分析 前言 随着5G、GPS导航、…
阅读更多...
《UDS协议从入门到精通》系列——图解0x84：安全数据传输

《UDS协议从入门到精通》系列——图解0x84：安全数据传输

《UDS协议从入门到精通》系列——图解0x84&#xff1a;安全数据传输 一、简介二、数据包格式2.1 服务请求格式2.2 服务响应格式2.2.1 肯定响应2.2.2 否定响应 Tip&#x1f4cc;&#xff1a;本文描述中但凡涉及到其他UDS服务的&#xff0c;将陆续提供链接跳转方式以便快速了解他…
阅读更多...
Python 3 CGI编程

Python 3 CGI编程

Python 3 CGI编程 引言 CGI（Common Gateway Interface）是一种重要的互联网技术，它允许 web 服务器执行外部程序来处理用户请求，并生成动态内容。尽管现代 web 开发中 CGI 的使用已经不如以前那么普遍，被诸如 PHP、Python 的 WSGI、Java 的 Servlet 等技术所取代，但了解…
阅读更多...
以太坊DApp交易量激增83%的背后原因解析

以太坊DApp交易量激增83%的背后原因解析

引言 最近&#xff0c;以太坊网络上的去中心化应用程序&#xff08;DApp&#xff09;交易量激增83%&#xff0c;引发了广泛关注和讨论。尽管交易费用高达2.4美元&#xff0c;但以太坊仍在DApp交易量方面遥遥领先于其他区块链网络。本文将深入探讨导致这一现象的主要原因&#…
阅读更多...
机器人控制系列教程之Delta机器人奇异性分析

机器人控制系列教程之Delta机器人奇异性分析

并联机器人奇异性 对于并联机构的奇异性问题比串联机构复杂。某些位形机构会失去自由度&#xff0c;某些位形机构会出现不可控自由度。其分析方法主要有几何法和代数法&#xff0c; 几何法&#xff1a; 即根据高等空间相关知识和机构中角度范围、干涉条件等推导出机构的奇异位…
阅读更多...
力扣Hot100-19删除链表的倒数第n个节点（双指针）

力扣Hot100-19删除链表的倒数第n个节点（双指针）

给你一个链表&#xff0c;删除链表的倒数第 n 个结点&#xff0c;并且返回链表的头结点。 示例 1&#xff1a; 输入&#xff1a;head [1,2,3,4,5], n 2 输出&#xff1a;[1,2,3,5]示例 2&#xff1a; 输入&#xff1a;head [1], n 1 输出&#xff1a;[]示例 3&#xff1a;…
阅读更多...
OpenCV 图像最小外包围矩形的绘制及长短边的计算

OpenCV 图像最小外包围矩形的绘制及长短边的计算

目录 一、概述 1.1意义 1.2应用 二、代码实现 三、实现效果 3.1原始图像 3.2处理后图像 3.3数据输出 一、概述 最小外包围矩形&#xff08;Minimum Bounding Rectangle, MBR&#xff09;在计算机视觉和图像处理中的意义和应用非常广泛。它是指能够完全包围目标的最小矩…
阅读更多...
phpexcel导入导出

phpexcel导入导出

前言&#xff1a; 如果你到处的excel软件打开有问题&#xff0c;下面有介绍解决办法 导入 1. composer init 初始化 2. 下载phpspreadsheet 这里需要注意php版本&#xff0c;需要大于7.2 composer require phpoffice/phpspreadsheet3. 编写代码 <?php require vendo…
阅读更多...
WPF 3D绘图 点云 系列五

WPF 3D绘图 点云 系列五

基本概念：点云是某个坐标系下的点的数据集。 可能包含丰富的信息，包括三维坐标X，Y，Z、颜色、分类值、强度值、时间等等 点云可以将现实世界原子化，通过高精度的点云数据可以还原现实世界。万物皆点云。 通过三维激光扫描仪进行数据采集获取点云数据，其次通过二维影像进行…
阅读更多...
Java | Leetcode Java题解之第213题打家劫舍II

Java | Leetcode Java题解之第213题打家劫舍II

题目&#xff1a; 题解&#xff1a; class Solution {public int rob(int[] nums) {int length nums.length;if (length 1) {return nums[0];} else if (length 2) {return Math.max(nums[0], nums[1]);}return Math.max(robRange(nums, 0, length - 2), robRange(nums, 1,…
阅读更多...
小试牛刀-区块链代币锁仓(Web页面)

小试牛刀-区块链代币锁仓(Web页面)

Welcome to Code Blocks blog 本篇文章主要介绍了 [区跨链代币锁仓(Web页面)] ❤博主广交技术好友&#xff0c;喜欢我的文章的可以关注一下❤ 目录 1.编写目的 2.开发环境 3.实现功能 4.代码实现 4.1 必要文件 4.1.1 ABI Json文件(LockerContractABI.json) 4.2 代码详解…
阅读更多...
AI绘画-Stable Diffusion 原理介绍及使用

AI绘画-Stable Diffusion 原理介绍及使用

引言 好像很多朋友对AI绘图有兴趣&#xff0c;AI绘画背后&#xff0c;依旧是大模型的训练。但绘图类AI对计算机显卡有较高要求。建议先了解基本原理及如何使用&#xff0c;在看看如何实现自己垂直行业的绘图AI逻辑。或者作为使用者&#xff0c;调用已有的server接口。 首先需…
阅读更多...
掌握Mojolicious会话管理：构建安全、持久的Web应用

掌握Mojolicious会话管理：构建安全、持久的Web应用

掌握Mojolicious会话管理&#xff1a;构建安全、持久的Web应用 Mojolicious是一个基于Perl的高性能、异步Web开发框架&#xff0c;它提供了一套完整的工具来构建现代Web应用。会话管理是Web开发中的一个关键组成部分&#xff0c;它允许应用识别和保持用户的登录状态。本文将深…
阅读更多...
单片机软件架构连载(3)-typedef

单片机软件架构连载(3)-typedef

今天给大家讲typedef&#xff0c;这个关键字在实际产品开发中&#xff0c;也是海量应用。 技术涉及知识点比较多&#xff0c;有些并不常用&#xff0c;我们以贴近实际为原则&#xff0c;让大家把学习时间都花在重点上。 1.typedef的概念 typedef 是 C 语言中的一个关键字&…
阅读更多...
WhatsApp机器人：提升客户服务效率的自动化工具

WhatsApp机器人：提升客户服务效率的自动化工具

在数字化转型的浪潮中&#xff0c;客户服务领域正经历着一场革命。WhatsApp机器人以其即时性、便捷性和高效性&#xff0c;正在成为企业提升客户服务效率的有力工具。 引言 客户服务是企业与用户建立信任和忠诚度的关键环节。然而&#xff0c;随着用户基数的增长&#xff0c;…
阅读更多...
DP：背包问题----0/1背包问题

DP：背包问题----0/1背包问题

文章目录 &#x1f497;背包问题&#x1f49b;背包问题的变体&#x1f9e1;0/1 背包问题的数学定义&#x1f49a;解决背包问题的方法&#x1f499;例子 &#x1f497;解决背包问题的一般步骤&#xff1f;&#x1f497;例题&#x1f497;总结 ❤️❤️❤️❤️❤️博客主页&…
阅读更多...
最新文章

Copyright @ 2022~2023