Load textfile content into a textEdit

Hi,
I wrote this sample code to test the situation described on the title:

Code:

Dialog::Dialog(QWidget *parent)
    : QDialog(parent), ui(new Ui::DialogClass)
{
    ui->setupUi(this);
    QFile A;
    QTemporaryFile B;
    A.setFileName(ui->filenameA->text());
    //B.setFileName(ui->filenameB->text());
    A.open(QFile::ReadOnly);
    B.open();
 
    QTextStream in(&A);
    QTextStream out(&B);
 
    QString line;
    do {
        line = in.readLine();
        out << "##" << line << endl;
    } while (!line.isNull());
    ui->textEditA->setPlainText(in.readAll());
    A.close();
    B.close();
}

in line 20 i want the content of the stream to be loaded into textEditA.
Where am i thinking wrong here?

Thanks