QGraphicsView Class

Public Types

flags	CacheMode
enum	CacheModeFlag { CacheNone, CacheBackground }
enum	DragMode { NoDrag, ScrollHandDrag, RubberBandDrag }
enum	OptimizationFlag { DontClipPainter, DontSavePainterState, DontAdjustForAntialiasing, IndirectPainting }
flags	OptimizationFlags
enum	ViewportAnchor { NoAnchor, AnchorViewCenter, AnchorUnderMouse }
enum	ViewportUpdateMode { FullViewportUpdate, MinimalViewportUpdate, SmartViewportUpdate, BoundingRectViewportUpdate, NoViewportUpdate }

Properties

alignment : Qt::Alignment backgroundBrush : QBrush cacheMode : CacheMode dragMode : DragMode foregroundBrush : QBrush interactive : bool optimizationFlags : OptimizationFlags

renderHints : QPainter::RenderHints resizeAnchor : ViewportAnchor rubberBandSelectionMode : Qt::ItemSelectionMode sceneRect : QRectF transformationAnchor : ViewportAnchor viewportUpdateMode : ViewportUpdateMode

• 3 properties inherited from QAbstractScrollArea
• 6 properties inherited from QFrame
• 59 properties inherited from QWidget
• 1 property inherited from QObject

Public Functions

	QGraphicsView(QWidget *parent = nullptr)
	QGraphicsView(QGraphicsScene *scene, QWidget *parent = nullptr)
virtual	~QGraphicsView()
Qt::Alignment	alignment() const
QBrush	backgroundBrush() const
QGraphicsView::CacheMode	cacheMode() const
void	centerOn(const QPointF &pos)
void	centerOn(qreal x, qreal y)
void	centerOn(const QGraphicsItem *item)
QGraphicsView::DragMode	dragMode() const
void	ensureVisible(const QRectF &rect, int xmargin = 50, int ymargin = 50)
void	ensureVisible(qreal x, qreal y, qreal w, qreal h, int xmargin = 50, int ymargin = 50)
void	ensureVisible(const QGraphicsItem *item, int xmargin = 50, int ymargin = 50)
void	fitInView(const QRectF &rect, Qt::AspectRatioMode aspectRatioMode = Qt::IgnoreAspectRatio)
void	fitInView(qreal x, qreal y, qreal w, qreal h, Qt::AspectRatioMode aspectRatioMode = ...)
void	fitInView(const QGraphicsItem *item, Qt::AspectRatioMode aspectRatioMode = Qt::IgnoreAspectRatio)
QBrush	foregroundBrush() const
bool	isInteractive() const
bool	isTransformed() const
QGraphicsItem *	itemAt(const QPoint &pos) const
QGraphicsItem *	itemAt(int x, int y) const
QList<QGraphicsItem *>	items() const
QList<QGraphicsItem *>	items(const QPoint &pos) const
QList<QGraphicsItem *>	items(int x, int y) const
QList<QGraphicsItem *>	items(const QRect &rect, Qt::ItemSelectionMode mode = Qt::IntersectsItemShape) const
QList<QGraphicsItem *>	items(int x, int y, int w, int h, Qt::ItemSelectionMode mode = Qt::IntersectsItemShape) const
QList<QGraphicsItem *>	items(const QPolygon &polygon, Qt::ItemSelectionMode mode = Qt::IntersectsItemShape) const
QList<QGraphicsItem *>	items(const QPainterPath &path, Qt::ItemSelectionMode mode = Qt::IntersectsItemShape) const
QPoint	mapFromScene(const QPointF &point) const
QPolygon	mapFromScene(const QRectF &rect) const
QPolygon	mapFromScene(const QPolygonF &polygon) const
QPainterPath	mapFromScene(const QPainterPath &path) const
QPoint	mapFromScene(qreal x, qreal y) const
QPolygon	mapFromScene(qreal x, qreal y, qreal w, qreal h) const
QPointF	mapToScene(const QPoint &point) const
QPolygonF	mapToScene(const QRect &rect) const
QPolygonF	mapToScene(const QPolygon &polygon) const
QPainterPath	mapToScene(const QPainterPath &path) const
QPointF	mapToScene(int x, int y) const
QPolygonF	mapToScene(int x, int y, int w, int h) const
QMatrix	matrix() const
QGraphicsView::OptimizationFlags	optimizationFlags() const
void	render(QPainter *painter, const QRectF &target = QRectF(), const QRect &source = QRect(), Qt::AspectRatioMode aspectRatioMode = Qt::KeepAspectRatio)
QPainter::RenderHints	renderHints() const
void	resetCachedContent()
void	resetMatrix()
void	resetTransform()
QGraphicsView::ViewportAnchor	resizeAnchor() const
void	rotate(qreal angle)
QRect	rubberBandRect() const
Qt::ItemSelectionMode	rubberBandSelectionMode() const
void	scale(qreal sx, qreal sy)
QGraphicsScene *	scene() const
QRectF	sceneRect() const
void	setAlignment(Qt::Alignment alignment)
void	setBackgroundBrush(const QBrush &brush)
void	setCacheMode(QGraphicsView::CacheMode mode)
void	setDragMode(QGraphicsView::DragMode mode)
void	setForegroundBrush(const QBrush &brush)
void	setInteractive(bool allowed)
void	setMatrix(const QMatrix &matrix, bool combine = false)
void	setOptimizationFlag(QGraphicsView::OptimizationFlag flag, bool enabled = true)
void	setOptimizationFlags(QGraphicsView::OptimizationFlags flags)
void	setRenderHint(QPainter::RenderHint hint, bool enabled = true)
void	setRenderHints(QPainter::RenderHints hints)
void	setResizeAnchor(QGraphicsView::ViewportAnchor anchor)
void	setRubberBandSelectionMode(Qt::ItemSelectionMode mode)
void	setScene(QGraphicsScene *scene)
void	setSceneRect(const QRectF &rect)
void	setSceneRect(qreal x, qreal y, qreal w, qreal h)
void	setTransform(const QTransform &matrix, bool combine = false)
void	setTransformationAnchor(QGraphicsView::ViewportAnchor anchor)
void	setViewportUpdateMode(QGraphicsView::ViewportUpdateMode mode)
void	shear(qreal sh, qreal sv)
QTransform	transform() const
QGraphicsView::ViewportAnchor	transformationAnchor() const
void	translate(qreal dx, qreal dy)
QTransform	viewportTransform() const
QGraphicsView::ViewportUpdateMode	viewportUpdateMode() const

Reimplemented Public Functions

virtual QVariant	inputMethodQuery(Qt::InputMethodQuery query) const override
virtual QSize	sizeHint() const override

• 20 public functions inherited from QAbstractScrollArea
• 14 public functions inherited from QFrame
• 214 public functions inherited from QWidget
• 31 public functions inherited from QObject
• 14 public functions inherited from QPaintDevice

Public Slots

void	invalidateScene(const QRectF &rect, QGraphicsScene::SceneLayers layers)
void	updateScene(const QList<QRectF> &rects)
void	updateSceneRect(const QRectF &rect)

• 19 public slots inherited from QWidget
• 1 public slot inherited from QObject

Signals

void	rubberBandChanged(QRect rubberBandRect, QPointF fromScenePoint, QPointF toScenePoint)

• 3 signals inherited from QWidget
• 2 signals inherited from QObject

Static Public Members

const QMetaObject

staticMetaObject

• 5 static public members inherited from QWidget
• 9 static public members inherited from QObject

Protected Functions

virtual void	drawBackground(QPainter *painter, const QRectF &rect)
virtual void	drawForeground(QPainter *painter, const QRectF &rect)

Reimplemented Protected Functions

virtual void	contextMenuEvent(QContextMenuEvent *event) override
virtual void	dragEnterEvent(QDragEnterEvent *event) override
virtual void	dragLeaveEvent(QDragLeaveEvent *event) override
virtual void	dragMoveEvent(QDragMoveEvent *event) override
virtual void	dropEvent(QDropEvent *event) override
virtual bool	event(QEvent *event) override
virtual void	focusInEvent(QFocusEvent *event) override
virtual bool	focusNextPrevChild(bool next) override
virtual void	focusOutEvent(QFocusEvent *event) override
virtual void	inputMethodEvent(QInputMethodEvent *event) override
virtual void	keyPressEvent(QKeyEvent *event) override
virtual void	keyReleaseEvent(QKeyEvent *event) override
virtual void	mouseDoubleClickEvent(QMouseEvent *event) override
virtual void	mouseMoveEvent(QMouseEvent *event) override
virtual void	mousePressEvent(QMouseEvent *event) override
virtual void	mouseReleaseEvent(QMouseEvent *event) override
virtual void	paintEvent(QPaintEvent *event) override
virtual void	resizeEvent(QResizeEvent *event) override
virtual void	scrollContentsBy(int dx, int dy) override
virtual void	showEvent(QShowEvent *event) override
virtual bool	viewportEvent(QEvent *event) override
virtual void	wheelEvent(QWheelEvent *event) override

• 20 protected functions inherited from QAbstractScrollArea
• 4 protected functions inherited from QFrame
• 35 protected functions inherited from QWidget
• 9 protected functions inherited from QObject
• 1 protected function inherited from QPaintDevice

Protected Slots

virtual void

setupViewport(QWidget *widget) override

• 1 protected slot inherited from QWidget

详细说明（Detailed Description）

    QGraphicsView图形视图类提供了一个QGraphicsScene图形场景窗口显示内容。

    QGraphicsView可以将QGraphicsScene中的内容在一个可滚动的视口中进行可视化。如何创建一个包含几何图形的场景可以参考QGraphicsScene。 QGraphicsView是Qt图形视图框架Graphics View Framework中的一个部件。

    可视化一个场景首先需要构建一个QGraphicsView对象，将要进行可视化的场景QGraphicsScene的地址传递给QGraphicsView的构造函数，或者稍后调用

void QGraphicsView::setScene(QGraphicsScene *scene)

进行场景设置，在调用

[slot] void QWidget::show()

后，视图将默认滚动到场景的中心，并显示任何可视的项目，例如：

  QGraphicsScene scene;
  scene.addText("Hello, world!");

  QGraphicsView view(&scene);
  view.show();

    可以通过使用滚动条或调用

void QGraphicsView::centerOn(const QPointF &pos)

显式的滚动到场景中的任何位置。将一个坐标位置传递给CenterOn()，QGraphicsView会滚动视口使该点在视图窗口上居中，CenterOn()的重载

void QGraphicsView::centerOn(const QGraphicsItem *item)

可以使某一个QGraphicsItem滚动并显示在视图的中心。如果只想确保某个区域在视图中是可见的（不一定需要在视图中心）时可以调用

void QGraphicsView::ensureVisible(const QRectF &rect, int xmargin = 50, int ymargin = 50)

    QGraphicsView可以用来可视化整个场景scene或者只显示其中的一部分。默认情况下当视图首次显示时调用

QRectF QGraphicsScene::itemsBoundingRect() const
//Calculates and returns the bounding rect of all items on the scene. 
//This function works by iterating over all items, and because of this, it can be slow for large scenes.

自动检测可视化区域，若要自己设置可视化区域可以调用

QRectF sceneRect() const
void setSceneRect(const QRectF &rect)
void setSceneRect(qreal x, qreal y, qreal w, qreal h)

这会适当的调整滚动条的范围。需要注意的是，场景几乎支持无限大小，但滚动条的范围不能超过整数的范围(INT_MIN, INT_MAX)。

    QGraphicsView通过调用render()对场景进行可视化。

void QGraphicsView::render(QPainter *painter, const QRectF &target = QRectF(), const QRect &source = QRect(), Qt::AspectRatioMode aspectRatioMode = Qt::KeepAspectRatio)

默认情况下，这些项目使用常规的QPainter和使用默认渲染方式呈现在视图窗口上，若要更改QGraphicsView在绘制项目时传递给QPainter的渲染方式，可以调用

QPainter::RenderHints renderHints() const
void setRenderHints(QPainter::RenderHints hints)

    默认情况下，QGraphicsView为视口小部件viewport提供了一个常规的QWidget。可以通过调用viewport()

QWidget *QAbstractScrollArea::viewport() const

访问这个窗口部件，或者调用

void QAbstractScrollArea::setViewport(QWidget *widget)

设置新的视图窗口若要使用OpenGL进行渲染，只需调用setViewport(new QGLWidget)，QGraphicsView是拥有视图窗口的所有权。

    QGraphicsView支持使用QTransform进行仿射变换。也可以调用

void QGraphicsView::setTransform(const QTransform &matrix, bool combine = false)

通过矩阵进行转换，或者调用以下几个函数

void QGraphicsView::rotate(qreal angle)

void QGraphicsView::scale(qreal sx, qreal sy)

void QGraphicsView::translate(qreal dx, qreal dy)

void QGraphicsView::shear(qreal sh, qreal sv)

最常见的两个转换是缩放和旋转。QGraphicsView在转换过程中视图的中心是保持固定不变的。由于场景对齐（(setAligment()），转换视图不会产生视觉上的影响。

    在QGraphicsView中，可以使用鼠标和键盘与场景中的项目交互，QGraphicsView将鼠标和键盘事件转换为scene事件(继承自QGraphicsSceneEvent)并将它们转换到可视化场景中，最后由单独的项目来处理这些事件并对它们作出响应。比如，单击一个可选项，该项目通常会通知场景它已被选中，并且会重绘自己以高亮显示选择矩形，如果你单击并使用鼠标拖动一个可移动的项目时，该项目会处理鼠标移动事件并移动它自己。默认情况下项目的交互是启用的，可以调用

bool isInteractive() const
void setInteractive(bool allowed)

进行切换。

    我们可以通过创建QGraphicsView的子类并重新实现鼠标和按键处理事件自定义场景交互。QGraphicsView提供了映射函数

QPointF QGraphicsView::mapToScene(const QPoint &point) const
//Returns the viewport coordinate point mapped to scene coordinates.

QPoint QGraphicsView::mapFromScene(const QPointF &point) const
//Returns the scene coordinate point to viewport coordinates.

以及项目访问函数。

QList<QGraphicsItem *> QGraphicsView::items() const
//Returns a list of all the items in the associated scene, in descending stacking 
//order (i.e., the first item in the returned list is the uppermost item).

QGraphicsItem *QGraphicsView::itemAt(const QPoint &pos) const
//Returns the item at position pos, which is in viewport coordinates. If there are 
//several items at this position, this function returns the topmost item.

这些项目可以让我们在视图坐标和场景坐标之间映射点、矩形、多边形和路径，并使用视图坐标在场景中查找项目。

 另外参考：QGraphicsScene, QGraphicsItem, QGraphicsSceneEvent