Showing QMainWindow Title bar

Hi,

in my application i need to show the title bar after some time i need to hide the title bar for that i am using following code
"HIding the title bar"

Code:

---

this->setWindowFlags(Qt::MSWindowsFixedSizeDialogHint);
    this->setWindowFlags(Qt::CustomizeWindowHint);
    this->setWindowFlags(Qt::FramelessWindowHint);

---

"Showing the title bar"

Code:

---

Qt::WindowFlags flags=windowFlags();
    flags^=Qt::WindowMinimizeButtonHint;
    setWindowFlags(flags);

---

But hiding works fine for me ,show make the application crashes

Regards
SivaKumar.N

on which line of code exactly does the code crash?
Run it in a debugger to see.