strange problem in QGraphicsView

[Shawn]

test::test(QWidget *parent, Qt::WFlags flags)
	: QMainWindow(parent, flags)
{
	ui.setupUi(this);
 
	QString str = "test";
	pixTrans.load("Resources/Trans.bmp");
 
	view.setScene(&scene);
	setCentralWidget(&view);
 
	showText(&str,0,0);
	showItem(&pixTrans,0,0);
	showText(&str,0,100);
	showItem(&pixTrans,0,100);
}
 
void test::showItem(QPixmap *pixmap, int x, int y)
{
	QGraphicsPixmapItem* i = scene.addPixmap(*pixmap);
	i->setPos(x,y);
}
void test::showText(QString *str, int x, int y)
{
	QGraphicsTextItem* i = scene.addText(*str);
	i->setPos(x, y);
}

test::test(QWidget *parent, Qt::WFlags flags)
	: QMainWindow(parent, flags)
{
	ui.setupUi(this);

	QString str = "test";
	pixTrans.load("Resources/Trans.bmp");

	view.setScene(&scene);
	setCentralWidget(&view);

	showText(&str,0,0);
	showItem(&pixTrans,0,0);
	showText(&str,0,100);
	showItem(&pixTrans,0,100);
}

void test::showItem(QPixmap *pixmap, int x, int y)
{
	QGraphicsPixmapItem* i = scene.addPixmap(*pixmap);
	i->setPos(x,y);
}
void test::showText(QString *str, int x, int y)
{
	QGraphicsTextItem* i = scene.addText(*str);
	i->setPos(x, y);
}

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the result is so strange:
the 1st text "test" at (0,0) is covered by the pixmap "pixTrans"
while the 2nd text "test" at (0,0) is on top of the pixmap "pixTrans"
I want to show text on top of pixmap at the same coordinate (x,y), is there any way to do this ?
thanks very much for suggestion!