为何这段代码加到Ondraw函数中还不能实现画出格子？
pDC->SelectStockObject(BLACK_PEN);
    CPoint pointA,pointB;
    pointA.x = pDoc->pointBegin.x;
    pointA.y = pDoc->pointBegin.y;
    pointB.x = pDoc->pointBegin.x+pDoc->nDistance*18;
    pointB.y = pDoc->pointBegin.y;
    for(int i=0;i<17;i++)//画横线
    {
        pointA.y+=pDoc->nDistance;
        pointB.y+=pDoc->nDistance;
        pDC->MoveTo(pointA);
        pDC->LineTo(pointB);
    }
    pointA.y=pDoc->pointBegin.y;
    pointB.x=pDoc->pointBegin.x;
    pointB.y=pDoc->pointBegin.y+pDoc->nDistance*18;
    for(i=0;i<17;i++)//画竖线
    {
        pointA.x+=pDoc->nDistance;
        pointB.x+=pDoc->nDistance;
        pDC->MoveTo(pointA);
        pDC->LineTo(pointB);
    }