Resize button with window and layout

[Radhika]

QWidget *w = new QWidget(this);
    QGridLayout *grid = new QGridLayout();
    ui->scrollArea->setWidget(w);
   // this->setFixedSize(this->geometry().width(),this->geometry().height());
 
 
    QMap<int,QPushButton*> mapp;
    for(row=0;row <= 49 ;row++)
    {
 
               QPushButton *pb = new QPushButton(w);
               grid->addWidget(pb, row/4, row%4);
               pb->setSizePolicy(QSizePolicy::Fixed,QSizePolicy::Expanding);
 
    }
 
    w->setLayout(grid);

QWidget *w = new QWidget(this);
    QGridLayout *grid = new QGridLayout();
    ui->scrollArea->setWidget(w);
   // this->setFixedSize(this->geometry().width(),this->geometry().height());


    QMap<int,QPushButton*> mapp;
    for(row=0;row <= 49 ;row++)
    {

               QPushButton *pb = new QPushButton(w);
               grid->addWidget(pb, row/4, row%4);
               pb->setSizePolicy(QSizePolicy::Fixed,QSizePolicy::Expanding);

    }

    w->setLayout(grid);

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Here it is

when I have tried
centralWidget()->setLayout(grid);
it ll shrink with window size but it wont fit in to the layout