call onPaint() with button click

Question

I have a picture control box (a CStatic) in a dialog. When the user presses a button in the dialog I need the onPaint() to draw an image in it. The problem is, The image is drawn at the loading of the dialog. How do I prevent this and call it only at button press.

My onPaint code;

void CStaticGraph::OnPaint()
{
    POINT xy[1000];
    CPaintDC dc(this); // device context for painting

    CRect Recto;
    char LocDim[80];

    GetWindowRect(&Recto);

    CPoint pBottom,pTop,pLeft;
    CPoint p[50];


    pBottom.SetPoint(0,0);
    pTop.SetPoint(0,Recto.Height());
    pLeft.SetPoint(Recto.Width(),Recto.Height());

    dc.MoveTo(pBottom);
    dc.LineTo(pTop);
    dc.LineTo(pLeft);

    int y[] ={80,120,180,200};
    int x=0;
    for(int i=0; i<sizeof(y);i++){
        p[i].SetPoint(Recto.Height()-x,y[i]);
        if(i>0){
                dc.MoveTo(p[i-1]);
                dc.LineTo(p[i]);


        }
        x+=50;
    }
}

As you can see I'm plotting a graph, I also need to pass data (the y[] values) at button press. I haven't done that yet.
Thanks.

Answer 1

Add a variable, such as a BOOL, to your CStaticGraph class to act as a flag to tell OnPaint() what to do. Initialize the variable in the constructor and change it when the button is clicked. For example:

In the header file for CStaticGraph add:

BOOL    m_fButtonPressed;

In the CStaticGraph constructor add:

m_fButtonPressed = FALSE;

In your button click handler do something like:

void CStaticGraph::OnButtonClick()
{
  m_fButtonPressed = TRUE;
  Invalidate();
}

Then in your OnPaint only draw the graph when flag is set:

void CStaticGraph::OnPaint()
(
  CPaintDC dc(this);

  if ( m_fButtonPressed )
  {
    // Clear the window
    return;
  }

  // Draw the graph
  . . .
}

Answer 2

In addition to the Invalidate() in the other answer, you need to also change

for(int i=0; i<sizeof(y);i++)

to

for(int i=0; i<sizeof(y)/sizeof(int);i++)