The program has unexpectedly finished.

[Guiom]

If you click in the button and no items are selected, ui->treeWidget->currentItem() return NULL.
And when the line ptr->isSelected() is executed, your program crash...
You need to add robustness.

[smemamian]

is it true ? :-?

void MainWindow::on_pushButton_clicked()
{
 
 
    for(int i=0 ; i<100 ;i++)
    {
        ui->progressBar->setValue(i);
        QThread::msleep(2);
    }
    if(ui->treeWidget->currentItem()->isSelected())
    {
    QTreeWidgetItem *ptr = ui->treeWidget->currentItem();
    ptr->setBackgroundColor(0,Qt::red);
    ptr->setBackgroundColor(1,Qt::red);
    }
}

void MainWindow::on_pushButton_clicked()
{


    for(int i=0 ; i<100 ;i++)
    {
        ui->progressBar->setValue(i);
        QThread::msleep(2);
    }
    if(ui->treeWidget->currentItem()->isSelected())
    {
    QTreeWidgetItem *ptr = ui->treeWidget->currentItem();
    ptr->setBackgroundColor(0,Qt::red);
    ptr->setBackgroundColor(1,Qt::red);
    }
}

To copy to clipboard, switch view to plain text mode 

[Guiom]

Nop, rather:

void MainWindow::on_pushButton_clicked()
{
    QTreeWidgetItem *ptr = ui->treeWidget->currentItem();
 
    for(int i=0 ; i<100 ;i++)
    {
        ui->progressBar->setValue(i);
        QThread::msleep(2);
    }
    if(ptr && ptr->isSelected())
    {
    ptr->setBackgroundColor(0,Qt::red);
    ptr->setBackgroundColor(1,Qt::red);
    }
}

void MainWindow::on_pushButton_clicked()
{
    QTreeWidgetItem *ptr = ui->treeWidget->currentItem();
 
    for(int i=0 ; i<100 ;i++)
    {
        ui->progressBar->setValue(i);
        QThread::msleep(2);
    }
    if(ptr && ptr->isSelected())
    {
    ptr->setBackgroundColor(0,Qt::red);
    ptr->setBackgroundColor(1,Qt::red);
    }
}

To copy to clipboard, switch view to plain text mode 

or use selectedItems().cout() ...

[ChrisW67]

Seems a rather pointless progress bar. Empty to full in 100 steps over 200 milliseconds... and then do the 'work' in fractions of a millisecond?