Can't write to external storage anymore under Android

#include <QApplication>
#include <QDialog>
#include <QLabel>
#include <QDir>
#include <QStandardPaths>
#include <QFile>
#include <QTextStream>
#include <QVBoxLayout>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QDialog dlg;

    dlg.setLayout( new QVBoxLayout() );

    QString path = QStandardPaths::writableLocation(QStandardPaths::DocumentsLocation);

    if ( !QDir(path).exists() )
    {
        if ( QDir().mkdir(path) )
            dlg.layout()->addWidget( new QLabel( "Could create folder " + path, &dlg ) );
        else
            dlg.layout()->addWidget( new QLabel( "Could NOT create folder " + path, &dlg ) );
    }
    else
    {
        dlg.layout()->addWidget( new QLabel( "Folder exists " + path, &dlg ) );
    }

    path += "/from_qt.txt";

    QFile file(path);
    if (file.open(QIODevice::ReadWrite))
    {
        QTextStream stream(&file);
        stream << "something" << endl;
        dlg.layout()->addWidget( new QLabel( "Could create file " + path, &dlg ) );
    }
    else
    {
        dlg.layout()->addWidget( new QLabel( "Could NOT create file " + path, &dlg ) );
    }

    dlg.show();
    return a.exec();
}