求救求救。。

Question

我用MFC编一个画图程序，为什么颜色那一块有问题？就是我开始画的时候和鼠标移动的时候颜色是对的，而当我再次点鼠标（画完图形后），颜色又变成黑的了？怎么回事？

Answer 1

void CMyView::OnLButtonDown(UINT nFlags, CPoint point) //lbottondown处理信息
{
CClientDC dc(this);
// TODO: Add your message handler code here and/or call default
CreatePen(PS_SOLID,0,m_color);
CBrush *CBrush=CBrush::FromHandle((HBRUSH)GetStockObject(NULL_BRUSH));
dc.SelectObject(CBrush);//....
if(DrawType==1)
{
if(m_step==0)
{
m_startx=point.x;
m_starty=point.y;
m_step++;
}
else
{
dc.MoveTo(m_startx,m_starty);
dc.LineTo(point.x,point.y);
          Cgraph *pgraph=new Cgraph(DrawType,m_startx,m_starty,point.x,point.y,m_color);
  m_ptrarray.Add(pgraph);                //添加图形到动态数组中
  CMyDoc*pDoc=GetDocument();
  ASSERT_VALID(pDoc);
  pDoc->AddGraph(DrawType,m_startx,m_starty,point.x,point.y,m_color);
  m_step=0;
  m_startx=m_starty=0;
  m_endx=m_endy=0;
}
}
if(DrawType==2)
{
if(m_step==0)
{
m_startx=point.x;
m_starty=point.y;
m_step++;
}
else
{
dc.Rectangle(m_startx,m_starty,point.x,point.y);
Cgraph *pgraph=new Cgraph(DrawType,m_startx,m_starty,point.x,point.y,m_color);
    m_ptrarray.Add(pgraph);
CMyDoc*pDoc=GetDocument();
    ASSERT_VALID(pDoc);
        pDoc->AddGraph(DrawType,m_startx,m_starty,point.x,point.y,m_color);
m_step=0;
m_startx=m_starty=0;
m_endx=m_endy=0;
}
}
if(DrawType==3)
{
if(m_step==0)
{
m_startx=point.x;
m_starty=point.y;
m_step++;
}
else
{
dc.Ellipse(m_startx,m_starty,point.x,point.y);
Cgraph *pgraph=new Cgraph(DrawType,m_startx,m_starty,point.x,point.y,m_color);
    m_ptrarray.Add(pgraph);
CMyDoc*pDoc=GetDocument();
       ASSERT_VALID(pDoc);
          pDoc->AddGraph(DrawType,m_startx,m_starty,point.x,point.y,m_color);
m_step=0;
m_startx=m_starty=0;
m_endx=m_endy=0;
}
}
if(DrawType==4)
{ if(m_step==0)
{
m_startx=point.x;
m_starty=point.y;
m_step++;
}
else
{
dc.MoveTo(m_startx,m_starty);
dc.LineTo(point.x,point.y);
Cgraph *pgraph=new Cgraph(DrawType,m_startx,m_starty,point.x,point.y,m_color);
    m_ptrarray.Add(pgraph);
CMyDoc*pDoc=GetDocument();
       ASSERT_VALID(pDoc);
          pDoc->AddGraph(DrawType,m_startx,m_starty,point.x,point.y,m_color);
m_step=0;
m_startx=m_starty=0;
m_endx=m_endy=0;
}
}
CView::OnLButtonDown(nFlags, point);
}void CMyView::OnLButtonUp(UINT nFlags, CPoint point) //lbottonup处理信息
{
// TODO: Add your message handler code here and/or call default
CMyDoc*pDoc=GetDocument();
ASSERT_VALID(pDoc);
CClientDC dc(this);
    CPen newPen;
newPen.CreatePen(PS_SOLID,0,m_color);
CBrush *CBrush=CBrush::FromHandle((HBRUSH)GetStockObject(NULL_BRUSH));
dc.SelectObject(CBrush);
dc.SelectObject(&newPen);
switch(DrawType)
{
case 1:
break;
case 2:

break;
case 3:

break;
case 4:

break;
case 5:
if(m_dragging)
{
       m_dragging=false;
        ReleaseCapture();
}
break;
}

CView::OnLButtonUp(nFlags, point);
}

Answer 2

 OnLButtonUp 里没画图要这段代码干嘛？ 出了这个函数newPen 没了 当然还原为默认画笔啦
 CPen newPen; 
newPen.CreatePen(PS_SOLID,0,m_color); 
CBrush *CBrush=CBrush::FromHandle((HBRUSH)GetStockObject(NULL_BRUSH)); 
dc.SelectObject(CBrush); 
dc.SelectObject(&newPen); 

Answer 3

OnLButtonDown 函数里反而没 SelectObject(&newPen) 不是在OnLButtonDown 里画吗？
逻辑真乱

Answer 4

要记住一点，绘图代码必须放在OnPaint或者会被OnPaint调用到的函数里面，否则只要窗口一重绘或者被其他窗口覆盖后移开，那么所有努力都将白费。
绘图放在OnLButtonDown里面本身就是一个设计错误。