VC mfc单文档中代码如下void CMyView::OnDraw(CDC* pDC) { CMyDoc* pDoc = GetDocument(); ASSERT_VALID(pDoc); for (int i=0;i<points.size();i++){ color=RGB(rand()%256,rand()%256,rand()%256); r=rand()%46+5; br.CreateSolidBrush(color); pDC->SelectObject(&br); pDC->Ellipse(points[i].x-r,points[i].y-r,points[i].x+r,points[i].y+r); br.DeleteObject(); } // TODO: add draw code for native data here } ///////////////////////////////////////////////////////////////////////////// // CMyView printing BOOL CMyView::OnPreparePrinting(CPrintInfo* pInfo) { // default preparation return DoPreparePrinting(pInfo); } void CMyView::OnBeginPrinting(CDC* /*pDC*/, CPrintInfo* /*pInfo*/) { // TODO: add extra initialization before printing } void CMyView::OnEndPrinting(CDC* /*pDC*/, CPrintInfo* /*pInfo*/) { // TODO: add cleanup after printing } ///////////////////////////////////////////////////////////////////////////// // CMyView diagnostics #ifdef _DEBUG void CMyView::AssertValid() const { CView::AssertValid(); } void CMyView::Dump(CDumpContext& dc) const { CView::Dump(dc); } CMyDoc* CMyView::GetDocument() // non-debug version is inline { ASSERT(m_pDocument->IsKindOf(RUNTIME_CLASS(CMyDoc))); return (CMyDoc*)m_pDocument; } #endif //_DEBUG ///////////////////////////////////////////////////////////////////////////// // CMyView message handlers void CMyView::OnLButtonDown(UINT nFlags, CPoint point) { // TODO: Add your message handler code here and/or call default center=point; r=rand()%46+5;//r=5~50 color=RGB(rand()%256,rand()%256,rand()%256); points.push_back(center); SetTimer(1,200,NULL); CView::OnLButtonDown(nFlags, point); } void CMyView::OnLButtonUp(UINT nFlags, CPoint point) { // TODO: Add your message handler code here and/or call default CView::OnLButtonUp(nFlags, point); } void CMyView::rise() { for(int i=0;i<points.size();i++) { points[i].y-=5; if(points[i].y<-r) { points.erase(points.begin()+i); i--; } } } void CMyView::OnTimer(UINT nIDEvent) { // TODO: Add your message handler code here and/or call default if(nIDEvent==1){ RedrawWindow(); rise(); } CView::OnTimer(nIDEvent); }，运行效果中圆在上升过程中颜色和大小不停的变换，应怎么修改此代码使得圆在上升过程中的大小和颜色不会变换，完整步骤及代码

要使圆在上升过程中大小和颜色不会变换，可以将颜色和大小的变化单独提取出来，放到循环外面进行定义，然后再在循环内部进行圆的上升操作。具体实现方式如下：

1. 在头文件中定义变量：

// 头文件中定义变量
COLORREF color; // 圆的颜色
int r; // 圆的半径

2. 在`OnDraw`函数中修改绘制圆的代码：

void CMyView::OnDraw(CDC* pDC)
{
    CMyDoc* pDoc = GetDocument();
    ASSERT_VALID(pDoc);

    // 绘制圆
    for (int i = 0;i < points.size();i++)
    {
        // 保持颜色和大小不变
        color = RGB(0, 0, 255); // 蓝色
        r = 20;

        // 绘制圆
        CPen pen(PS_SOLID, 1, color);
        CBrush brush(color);
        pDC->SelectObject(&pen);
        pDC->SelectObject(&brush);
        pDC->Ellipse(points[i].x - r, points[i].y - r, points[i].x + r, points[i].y + r);
    }
}

在这个代码中，我们将颜色和大小的变化都删除了，直接将颜色设置为蓝色，大小设置为20。这样就可以让圆在上升过程中保持颜色和大小不变了。

完整修改后的代码如下：

MyView.h文件：

#pragma once

#include "MyDoc.h"
#include <vector>

class CMyView : public CView
{
protected: // create from serialization only
    CMyView() noexcept;
    DECLARE_DYNCREATE(CMyView)

// Attributes
public:
    CMyDoc* GetDocument() const;

// Operations
public:

// Overrides
public:
    virtual void OnDraw(CDC* pDC) override;
    virtual BOOL PreCreateWindow(CREATESTRUCT& cs);
protected:
    virtual void OnInitialUpdate() override; // called first time after construct
    virtual void OnUpdate(CView* /*pSender*/, LPARAM /*lHint*/, CObject* /*pHint*/) override;

// Implementation
public:
    virtual ~CMyView();
#ifdef _DEBUG
    virtual void AssertValid() const;
    virtual void Dump(CDumpContext& dc) const;
#endif

protected:

// Generated message map functions
protected:
    DECLARE_MESSAGE_MAP()
public:
    afx_msg void OnLButtonDown(UINT nFlags, CPoint point);
    afx_msg void OnLButtonUp(UINT nFlags, CPoint point);
    afx_msg void OnTimer(UINT_PTR nIDEvent);
    void rise();
};

#ifndef _DEBUG  // debug version in MyView.cpp
inline CMyDoc* CMyView::GetDocument() const
   { return reinterpret_cast<CMyDoc*>(m_pDocument); }
#endif

MyView.cpp文件：

#include "pch.h"
#include "framework.h"
#include "My.h"
#include "MyDoc.h"
#include "MyView.h"

#ifdef _DEBUG
#define new DEBUG_NEW
#endif

IMPLEMENT_DYNCREATE(CMyView, CView)

BEGIN_MESSAGE_MAP(CMyView, CView)
    ON_WM_LBUTTONDOWN()
    ON_WM_LBUTTONUP()
    ON_WM_TIMER()
END_MESSAGE_MAP()

// CMyView construction/destruction

CMyView::CMyView() noexcept
{
    // TODO: add construction code here

}

CMyView::~CMyView()
{
}

BOOL CMyView::PreCreateWindow(CREATESTRUCT& cs)
{
    // TODO: Modify the Window class or styles here by modifying
    //  the CREATESTRUCT cs

    return CView::PreCreateWindow(cs);
}

// CMyView drawing

void CMyView::OnDraw(CDC* pDC)
{
    CMyDoc* pDoc = GetDocument();
    ASSERT_VALID(pDoc);

    // 绘制圆
    for (int i = 0;i < points.size();i++)
    {
        // 保持颜色和大小不变
        color = RGB(0, 0, 255); // 蓝色
        r = 20;

        // 绘制圆
        CPen pen(PS_SOLID, 1, color);
        CBrush brush(color);
        pDC->SelectObject(&pen);
        pDC->SelectObject(&brush);
        pDC->Ellipse(points[i].x - r, points[i].y - r, points[i].x + r, points[i].y + r);
    }
}

void CMyView::OnInitialUpdate()
{
    CView::OnInitialUpdate();

    // TODO: Add your specialized code here and/or call the base class

}

void CMyView::OnUpdate(CView* /*pSender*/, LPARAM /*lHint*/, CObject* /*pHint*/)
{
    CMyDoc* pDoc = GetDocument();
    ASSERT_VALID(pDoc);
    if (!pDoc)
        return;

    // TODO: Add your specialized code here and/or call the base class

}

// CMyView diagnostics

#ifdef _DEBUG
void CMyView::AssertValid() const
{
    CView::AssertValid();
}

void CMyView::Dump(CDumpContext& dc) const
{
    CView::Dump(dc);
}

CMyDoc* CMyView::GetDocument() const // non-debug version is inline
{
    ASSERT(m_pDocument->IsKindOf(RUNTIME_CLASS(CMyDoc)));
    return (CMyDoc*)m_pDocument;
}
#endif //_DEBUG

// CMyView message handlers

void CMyView::OnLButtonDown(UINT nFlags, CPoint point)
{
    // TODO: Add your message handler code here and/or call default

    center = point;
    r = rand() % 46 + 5;
    color = RGB(rand() % 256, rand() % 256, rand() % 256);

    points.push_back(center);
    SetTimer(1, 200, NULL);

    CView::OnLButtonDown(nFlags, point);
}

void CMyView::OnLButtonUp(UINT nFlags, CPoint point)
{
    // TODO: Add your message handler code here and/or call default

    CView::OnLButtonUp(nFlags, point);
}

void CMyView::rise()
{
    for (int i = 0;i < points.size();i++)
    {
        points[i].y -= 5;
        if (points[i].y < -r)
        {
            points.erase(points.begin() + i);
            i--;
        }
    }
}

void CMyView::OnTimer(UINT_PTR nIDEvent)
{
    // TODO: Add your message handler code here and/or call default

    if (nIDEvent == 1) {
        RedrawWindow();
        rise();
    }

    CView::OnTimer(nIDEvent);
}

这样修改后，圆在上升过程中的大小和颜色就不会变换了。