Yes, the styleName is in the list that QStyleFactory::keys returns for example i set "plastique":
Qt Code: 
  1. QApplication::setStyle(QStyleFactory::create("plastique"));
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Yes the platform style is used by default, but my problem is, i set a style like ("plastique") and can't reset to the platform default style.

In Qt 3.3 i can do it with:
Qt Code: 
  1. QApplication::setStyle(0);
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but Qt 4.2 do nothing.

The problem is not a dependent style like "windowsxp" and "macintosh", you know what i mean?