qt error: variable `QPainter painter' has initializer but incomplete type

QT中出现：error: variable `QPainter painter' has initializer but incomplete type

#include "picture.h"

#include "ui_picture.h"
#include"qpainter.h"  //一开始在我自己的.cpp中没有加上这个声明，出现了那个错误，加上即可
picture::picture(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::picture)
{
    ui->setupUi(this);
}

void picture::draw()
{
   QPainter painter (this );
   //painter.setPen( QPen( black, 8, DashDotLine) );
   //painter.setBrush( QBrush( red, Dense6Pattern) );
   //painter.drawEllipse( 20, 20, 100, 60 );
   painter


}




picture::~picture()
{
    delete ui;
}