[MFC] Refreshing Picture Control

Hello,
I have a problem. I'm trying to create an application, which shows a rectangle on a grid. The position of the rectangle is subject to coordinates given from GPS simulator. The application is based on a single dialog window which involves a Picture Control. I set a type of that as Owner Draw. Then I created a class CPict, based on CStatic. CPict involves the OnPaint() method. Then I created a control variable of Picture Control. It's a CPict type variable named m_pict. In the class CGPSDlg there is the OnRead() method. To invoke that method, the user have to click a button. My question is: how to refresh the content of the Picture Control in OnRead() method. Here's some code:

Code:

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void CGPSDlg::OnRead()
{
        CComPort* pComPort = new CComPort(g_sComPort);
        if (pComPort->Initialize())
        {
                pComPort->Read(m_sResults);
                m_sLatitude = m_sResults;
                m_sLatitude.Delete(0,19);
                m_sLatitude.Delete(2,50);
                m_nLatitude = atoi(m_sLatitude);
                pComPort->Terminate();
        }
        else
        {
                m_sResults = "Setup failed";
        }
        UpdateData(FALSE);
}

---

Code:

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void CPict::OnPaint()
{
        CPaintDC dc(this);
        CDC mdc;
        mdc.CreateCompatibleDC(&dc);
        CBitmap mBitmap;
        CBitmap* pOldMap;
        mBitmap.CreateCompatibleBitmap(&dc,360,180);
        pOldMap = mdc.SelectObject(&mBitmap);
        CBrush* pOldBrush;
        CPen* pOldPen;
        CBrush aWhiteBrush;
        aWhiteBrush.CreateSolidBrush(RGB(255,0,0));
        CPen BlackPen(PS_SOLID,1,RGB(255,255,255));
        pOldPen = mdc.SelectObject(&BlackPen);
        pOldBrush = mdc.SelectObject(&aWhiteBrush);
        mdc.SetMapMode(MM_ANISOTROPIC);
        CGPSDlg m_bridge;
        y=m_bridge.m_nLatitude;     
        for(int i=1;i<36;i++){
                mdc.MoveTo(i*10,0); mdc.LineTo(i*10,180);}
        for(int i=1;i<18;i++){
                mdc.MoveTo(0,i*10); mdc.LineTo(360,i*10);}
        CString str;
        str = m_bridge.m_sResults;
        mdc.Rectangle(10,y-3,16,y+3);
        mdc.TextOutA(10,10,str);
        dc.BitBlt(0,0,500,360,&mdc,0,0,SRCCOPY);
}

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Please use code tags for posting readable code.

You can use Invalidate to force a window to redraw itself.

Some notes on your code.

In the OnRead...

Code:

---

CComPort* pComPort = new CComPort(g_sComPort);

---

This is never freed, so you have a memory leak.

In the OnPaint...

Code:

---

CGPSDlg m_bridge;
y=m_bridge.m_nLatitude;

---

You are creating a new window in the OnPaint. This will slow down your paint, because creating a new window is relatively a intensive job, and the OnPaint can be triggered a lot of times without you knowing it. Also, the class is new, so the m_nLatitude has it's default value, not the value you put in there during the OnRead function.

Then how to transfer values from OnRead() to update them in OnPaint() ?

You can pass the pointer of 1 class to another.

Something like this...

Code:

---

class A
{
public:

  int MyVariable;

};



class B
{
public:

  A *MyA;
 
  void SomeFunction ()
  {
      MyA->MyVariable = 10;
  }

};



int main ()
{
  A varA;
  B varB;

  varB.MyA = &varA;                // set the pointer of varA
  varB.SomeFunction ();            // this function uses the varA-pointer to set MyVariable

};

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