在qt5 pieview中画条形图，有代码 求高手讲解一下，急求！！！！！

Question

#include "pieview.h"
#include

PieView::PieView(QWidget *parent) :
QAbstractItemView(parent)
{
}

void PieView::paintEvent(QPaintEvent *)
{
QPainter painter(viewport());
painter.setPen(Qt::black);
int x0=40;
int y0=250;
//y坐标轴
painter.drawLine(x0,y0,40,30);
painter.drawLine(38,32,40,30);
painter.drawLine(40,30,42,32);
painter.drawText(20,30,tr("销售数量"));
for(int i=1;i<5;i++)
{
painter.drawLine(-1,-i*50,1,-i*50);
painter.drawText(-20,-i*50,tr("%1").arg(i*5));
}
//x 坐标轴
painter.drawLine(x0,y0,540,250);
painter.drawLine(538,248,540,250);
painter.drawLine(540,250,538,252);
painter.drawText(545,250,tr("品牌"));

int pos=x0+20;
int row;
for(row=0;row<model()->rowCount(rootIndex());row++)
{
    QModelIndex index=model()->index(row,0,rootIndex());
    QString dep=model()->data(index).toString();

    painter.drawText(pos,y0+20,dep);
    pos+=50;
}
int posN=x0+20;
for(row=0;row<model()->rowCount(rootIndex());row++)
{
    QModelIndex index=model()->index(row,1,rootIndex());
    int sell=model()->data(index).toDouble();

    int width=10;
    QModelIndex colorIndex = model()->index(row,0,rootIndex());
    QColor color = QColor(model()->data(colorIndex,Qt::DecorationRole).toString());
    if(selections->isSelected(index))
        painter.setBrush(QBrush(color,Qt::Dense3Pattern));
    else
        painter.setBrush(QBrush(color));

    painter.drawRect(QRect(posN,y0-sell*10,width,sell*10));
    QRegion regionM(posN,y0-sell*10,width,sell*10);
    RegionList<<regionM;

    posN+=50;
}

}

void PieView::setSelectionModel(QItemSelectionModel *selectionModel)
{
selections = selectionModel;
}

QRegion PieView::itemRegion(QModelIndex index)
{
QRegion region;
if (index.column() == 1) // 销售数量
region = RegionList[index.row()];
return region;
}

QModelIndex PieView::indexAt(const QPoint &point) const
{
QPoint newPoint(point.x(),point.y());
QRegion region;
foreach(region,RegionList) // 销售数量 列
{
if (region.contains(newPoint))
{
int row = RegionList.indexOf(region);
QModelIndex index = model()->index(row,1,rootIndex());
return index;
}
}
return QModelIndex();
}

QRect PieView::visualRect(const QModelIndex &index) const{}
void PieView::scrollTo(const QModelIndex &index, ScrollHint hint){}
QModelIndex PieView::moveCursor(CursorAction cursorAction, Qt::KeyboardModifiers modifiers){}
int PieView::horizontalOffset()const{}
int PieView::verticalOffset()const{}
bool PieView::isIndexHidden(const QModelIndex &index) const{}
void PieView::setSelection(const QRect &rect, QItemSelectionModel::SelectionFlags command){}
QRegion PieView::visualRegionForSelection(const QItemSelection &selection) const{}