#include "canvasforu_t.h"

canvasForU_T::canvasForU_T(QWidget* parent):QWidget(parent)
{
    paint=new QPainter(this);
}

void canvasForU_T::paintEvent(QPaintEvent *){

    //QPainter paint(this);

    paint->drawLine(0,0,170,170);

}

canvasForU_T::~canvasForU_T(){
    delete paint;
}

painter= new QPainter(this);
...
delete painter;

QPainter painter(this);

//это к делу не относится, просто подправил ))
MainWindow::~MainWindow()
{
   delete ui;
   delete pictureU_T,
   delete pictureU_X;
}


//а это оно самое
/*
void MainWindow::paintEvent(QPaintEvent*){
    painter= new QPainter(this);
    QColor color(Qt::blue);
    QPen pen(color);
    pen.setWidth(8);
    painter->setPen(pen);
    //this->pictureU_T->update();
}
*/
void MainWindow::paintEvent(QPaintEvent*)
{
    QPainter painter(this);
    QColor color(Qt::blue);
    QPen pen(color);
    pen.setWidth(8);
    painter.setPen(pen);
}