为什么使用QGraphicsView::scale， 当scale的参数小于1时我的QGraphicsScene上的item就全部消失了？

#include "iitems.h"

#include <QtGui>

#include "Link.h"

#include "Node.h"

#include "propertiesdialog.h"

#include <QWidget>



extern float Xmax,Ymax;

extern int VisZoom;

extern float iData[6376][3];

extern float xx,yy;



iItems::iItems()

{

	QSplitter *MainSplitter = new QSplitter(Qt::Horizontal);

	QSplitter * WidgetRight = new QSplitter(Qt::Vertical);

	QWidget *SubWidget1 = new QWidget;

	QWidget *SubWidget2 = new QWidget;



	//QWidget *area= new QWidget;

	view = new QGraphicsView;



	spinBox1 = new QSpinBox;

	QSlider *slider1 = new QSlider(Qt::Horizontal);

	spinBox1->setRange(1, 9);

	spinBox1->setValue(1);

	SpinBoxValue1=spinBox1->value();

    VisZoom=10;

	slider1->setRange(1, 9);



	QObject::connect(spinBox1, SIGNAL(valueChanged(int)),

		slider1, SLOT(setValue(int)));

	QObject::connect(slider1, SIGNAL(valueChanged(int)),

		spinBox1, SLOT(setValue(int)));

	QObject::connect(spinBox1, SIGNAL(valueChanged(int)),

		this, SLOT(setVisZoom()));



	QHBoxLayout *layout1 = new QHBoxLayout;

	layout1->addWidget(spinBox1);

	layout1->addWidget(slider1);

	SubWidget1->setLayout(layout1);



	QSpinBox *spinBox2 = new QSpinBox;

	QSlider *slider2 = new QSlider(Qt::Horizontal);

	spinBox2->setRange(0, 130);

	spinBox2->setValue(25);

	slider2->setRange(0, 130);

	QObject::connect(spinBox2, SIGNAL(valueChanged(int)),

		slider2, SLOT(setValue(int)));

	QObject::connect(slider2, SIGNAL(valueChanged(int)),

		spinBox2, SLOT(setValue(int)));



	QHBoxLayout *layout2 = new QHBoxLayout;

	layout2->addWidget(spinBox2);

	layout2->addWidget(slider2);

	SubWidget2->setLayout(layout2);



	WidgetRight->addWidget(SubWidget1);

	WidgetRight->addWidget(SubWidget2);



	MainSplitter->addWidget(view);

	MainSplitter->addWidget(WidgetRight);



	view->setDragMode(QGraphicsView::RubberBandDrag);// 选择多个节点方式：1.按ctrl；2.设置橡皮筋方式

	view->setRenderHints(QPainter::Antialiasing

		| QPainter::TextAntialiasing);

	view->setContextMenuPolicy(Qt::ActionsContextMenu);// 右键菜单

	setCentralWidget(MainSplitter);



	scene = new QGraphicsScene(0, 0, Xmax*VisZoom, Ymax*VisZoom);// 创建场景，起始点为(0,0), 宽600，高500

	view->setScene(scene);// 显示场景

	view->setStyleSheet("background-color:gray");



	minZ = 0;

	maxZ = 0;

	seqNumber = 0;

	createActions();

	createMenus();

	createToolBars();

	connect(scene, SIGNAL(selectionChanged()),

		this, SLOT(updateActions()));

	setWindowTitle(tr("Diagram"));

	updateActions();

}





// 增加一个节点

void iItems::addNode1()

{

	Node *node = new Node;

	node->setText(tr("Node %1").arg(seqNumber + 1));

	setupNode1(node);

}



void iItems::setupNode1(Node *node)

{

	node->setPos(QPoint(80 + (100 * (seqNumber % 5)),



		80 + (50 * ((seqNumber / 5) % 7))));

	scene->addItem(node);

	++seqNumber;

	scene->clearSelection();

	node->setSelected(true);

	bringToFront();

}



void iItems::bringToFront()

{

	++maxZ;

	setZValue(maxZ);

}

void iItems::sendToBack()

{

	--minZ;

	setZValue(minZ);

}

void iItems::setZValue(int z)

{

	Node *node = selectedNode();

	if (node)

		node->setZValue(z);

}



Node *iItems::selectedNode() const

{

	QList<QGraphicsItem *> items = scene->selectedItems();

	if (items.count() == 1) {

		return dynamic_cast<Node *>(items.first());

	} else {

		return 0;

	}

}



void iItems::addLink()

{

	NodePair nodes = selectedNodePair();

	if (nodes == NodePair())

		return;

	Link *link = new Link(nodes.first, nodes.second);

	scene->addItem(link);

}