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public interface QGraphicsLayoutItemInterface
The QGraphicsLayoutItem
class can be inherited to allow your custom items to be managed by layouts. QGraphicsLayoutItem
is an abstract class that defines a set of virtual functions describing sizes, size policies, and size hints for any object arranged by QGraphicsLayout
. The API contains functions relevant for both the item itself and for the user of the item as most of QGraphicsLayoutItem
's functions are also part of the subclass' public API.
In most cases, existing layout-aware classes such as QGraphicsWidget
and QGraphicsLayout
already provide the functionality you require. However, subclassing these classes will enable you to create both graphical elements that work well with layouts (QGraphicsWidget
) or custom layouts (QGraphicsLayout
).Subclassing QGraphicsLayoutItem
If you create a subclass of QGraphicsLayoutItem
and reimplement its virtual functions, you will enable the layout to resize and position your item along with other QGraphicsLayoutItems
including QGraphicsWidget
and QGraphicsLayout
.
You can start by reimplementing important functions: the protected sizeHint()
function, as well as the public setGeometry()
function. If you want your items to be aware of immediate geometry changes, you can also reimplement updateGeometry()
.
The geometry, size hint, and size policy affect the item's size and position. Calling setGeometry()
will always resize and reposition the item immediately. Normally, this function is called by QGraphicsLayout
after the layout has been activated, but it can also be called by the item's user at any time.
The sizeHint()
function returns the item' minimum, preferred and maximum size hints. You can override these properties by calling setMinimumSize()
, setPreferredSize()
or setMaximumSize()
. You can also use functions such as setMinimumWidth()
or setMaximumHeight()
to set only the width or height component if desired.
The effectiveSizeHint()
function, on the other hand, returns a size hint for any given Qt::SizeHint
, and guarantees that the returned size is bound to the minimum and maximum sizes and size hints. You can set the item's vertical and horizontal size policy by calling setSizePolicy()
. The sizePolicy
property is used by the layout system to describe how this item prefers to grow or shrink.Nesting QGraphicsLayoutItems
QGraphicsLayoutItems
can be nested within other QGraphicsLayoutItems
, similar to layouts that can contain sublayouts. This is done either by passing a QGraphicsLayoutItem
pointer to QGraphicsLayoutItem
's protected constructor, or by calling setParentLayoutItem()
. The parentLayoutItem()
function returns a pointer to the item's layoutItem
parent. If the item's parent is 0 or if the the parent does not inherit from QGraphicsItem
, the parentLayoutItem()
function then returns 0. isLayout()
returns true if the QGraphicsLayoutItem
subclass is itself a layout, or false otherwise.
Qt uses QGraphicsLayoutItem
to provide layout functionality in the The Graphics View Framework, but in the future its use may spread throughout Qt itself.
QGraphicsWidget
, QGraphicsLayout
, QGraphicsLinearLayout
, and QGraphicsGridLayout
.
Method Summary | |
---|---|
QRectF |
contentsRect()
Returns the contents rect in local coordinates. |
QSizeF |
effectiveSizeHint(Qt.SizeHint which,
QSizeF constraint)
Returns the effective size hint for this QGraphicsLayoutItem . |
QRectF |
geometry()
Returns the item's geometry (e.g., position and size) as a QRectF. |
com.trolltech.qt.gui.QMarginsF |
getContentsMargins()
This virtual function provides the left, top, right and bottom contents margins for this QGraphicsLayoutItem . |
boolean |
isLayout()
Returns true if this QGraphicsLayoutItem is a layout (e.g., is inherited by an object that arranges other QGraphicsLayoutItem objects); otherwise returns false. |
double |
maximumHeight()
Returns the maximum height. |
QSizeF |
maximumSize()
Returns the maximum size. |
double |
maximumWidth()
Returns the maximum width. |
double |
minimumHeight()
Returns the minimum height. |
QSizeF |
minimumSize()
Returns the minimum size. |
double |
minimumWidth()
Returns the minimum width. |
QGraphicsLayoutItemInterface |
parentLayoutItem()
Returns the parent of this QGraphicsLayoutItem , or 0 if there is no parent, or if the parent does not inherit from QGraphicsLayoutItem (QGraphicsLayoutItem is often used through multiple inheritance with QObject -derived classes). |
double |
preferredHeight()
Returns the preferred height. |
QSizeF |
preferredSize()
Returns the preferred size. |
double |
preferredWidth()
Returns the preferred width. |
void |
setGeometry(QRectF rect)
This pure virtual function sets the geometry of the QGraphicsLayoutItem to rect, which is in parent coordinates (e.g., the top-left corner of rect is equivalent to the item's position in parent coordinates). |
void |
setMaximumHeight(double height)
Sets the maximum height to height. |
void |
setMaximumSize(double w,
double h)
This convenience function is equivalent to calling setMaximumSize(QSizeF(w, h)). |
void |
setMaximumSize(QSizeF size)
Sets the maximum size to size. |
void |
setMaximumWidth(double width)
Sets the maximum width to width. |
void |
setMinimumHeight(double height)
Sets the minimum height to height. |
void |
setMinimumSize(double w,
double h)
This convenience function is equivalent to calling setMinimumSize(QSizeF(w, h)). |
void |
setMinimumSize(QSizeF size)
Sets the minimum size to size. |
void |
setMinimumWidth(double width)
Sets the minimum width to width. |
void |
setParentLayoutItem(QGraphicsLayoutItemInterface parent)
Sets the parent of this QGraphicsLayoutItem to parent. |
void |
setPreferredHeight(double height)
Sets the preferred height to height. |
void |
setPreferredSize(double w,
double h)
This convenience function is equivalent to calling setPreferredSize(QSizeF(w, h)). |
void |
setPreferredSize(QSizeF size)
Sets the preferred size to size. |
void |
setPreferredWidth(double width)
Sets the preferred width to width. |
void |
setSizePolicy(QSizePolicy.Policy hPolicy,
QSizePolicy.Policy vPolicy,
QSizePolicy.ControlType controlType)
This function is equivalent to calling setSizePolicy( QSizePolicy (hPolicy, vPolicy, controlType)). |
void |
setSizePolicy(QSizePolicy policy)
Sets the size policy to policy. |
QSizeF |
sizeHint(Qt.SizeHint which,
QSizeF constraint)
This pure virtual function returns the size hint for which of the QGraphicsLayoutItem , using the width or height of constraint to constrain the output. |
QSizePolicy |
sizePolicy()
Returns the current size policy. |
void |
updateGeometry()
This virtual function discards any cached size hint information. |
Methods inherited from interface com.trolltech.qt.QtJambiInterface |
---|
disableGarbageCollection, nativeId, nativePointer, reenableGarbageCollection, setJavaOwnership |
Method Detail |
---|
QRectF contentsRect()
The contents rect defines the subrectangle used by an associated layout when arranging subitems. This function is a convenience function that adjusts the item's geometry()
by its contents margins. Note that getContentsMargins()
is a virtual function that you can reimplement to return the item's contents margins.
getContentsMargins()
, and geometry()
.
QSizeF effectiveSizeHint(Qt.SizeHint which, QSizeF constraint)
QGraphicsLayoutItem
. which is the size hint in question. constraint is an optional argument that defines a special constrain when calculating the effective size hint. By default, constraint is QSizeF(-1, -1), which means there is no constraint to the size hint.
If you want to specify the widget's size hint for a given width or height, you can provide the fixed dimension in constraint. This is useful for widgets that can grow only either vertically or horizontally, and need to set either their width or their height to a special value.
For example, a text paragraph item fit into a column width of 200 may grow vertically. You can pass QSizeF(200, -1) as a constraint to get a suitable minimum, preferred and maximum height).
You can adjust the effective size hint by reimplementing sizeHint()
in a QGraphicsLayoutItem
subclass, or by calling one of the following functions: setMinimumSize()
, setPreferredSize
, or setMaximumSize()
(or a combination of both).
This function caches each of the size hints and guarantees that sizeHint()
will be called only once for each value of which - unless constraint is not specified and updateGeometry()
has been called.
sizeHint()
.
QRectF geometry()
pos()
, size()). setGeometry()
.
boolean isLayout()
QGraphicsLayoutItem
is a layout (e.g., is inherited by an object that arranges other QGraphicsLayoutItem
objects); otherwise returns false. QGraphicsLayout
.
double maximumHeight()
setMaximumHeight()
, setMaximumSize()
, and maximumSize()
.
QSizeF maximumSize()
setMaximumSize()
, minimumSize()
, preferredSize()
, Qt::MaximumSize
, and sizeHint()
.
double maximumWidth()
setMaximumWidth()
, setMaximumSize()
, and maximumSize()
.
double minimumHeight()
setMinimumHeight()
, setMinimumSize()
, and minimumSize()
.
QSizeF minimumSize()
setMinimumSize()
, preferredSize()
, maximumSize()
, Qt::MinimumSize
, and sizeHint()
.
double minimumWidth()
setMinimumWidth()
, setMinimumSize()
, and minimumSize()
.
QGraphicsLayoutItemInterface parentLayoutItem()
QGraphicsLayoutItem
, or 0 if there is no parent, or if the parent does not inherit from QGraphicsLayoutItem
(QGraphicsLayoutItem
is often used through multiple inheritance with QObject
-derived classes). setParentLayoutItem()
.
double preferredHeight()
setPreferredHeight()
, setPreferredSize()
, and preferredSize()
.
QSizeF preferredSize()
setPreferredSize()
, minimumSize()
, maximumSize()
, Qt::PreferredSize
, and sizeHint()
.
double preferredWidth()
setPreferredWidth()
, setPreferredSize()
, and preferredSize()
.
void setMaximumHeight(double height)
maximumHeight()
, setMaximumSize()
, and maximumSize()
.
void setMaximumSize(QSizeF size)
sizeHint()
for Qt::MaximumSize
and ensures that effectiveSizeHint()
will never return a size larger than size. In order to unset the maximum size, use an invalid size. maximumSize()
, minimumSize()
, preferredSize()
, Qt::MaximumSize
, and sizeHint()
.
void setMaximumSize(double w, double h)
maximumSize()
, setMinimumSize()
, setPreferredSize()
, and sizeHint()
.
void setMaximumWidth(double width)
maximumWidth()
, setMaximumSize()
, and maximumSize()
.
void setMinimumHeight(double height)
minimumHeight()
, setMinimumSize()
, and minimumSize()
.
void setMinimumSize(QSizeF size)
sizeHint()
for Qt::MinimumSize
and ensures that effectiveSizeHint()
will never return a size smaller than size. In order to unset the minimum size, use an invalid size. minimumSize()
, maximumSize()
, preferredSize()
, Qt::MinimumSize
, sizeHint()
, setMinimumWidth()
, and setMinimumHeight()
.
void setMinimumSize(double w, double h)
minimumSize()
, setMaximumSize()
, setPreferredSize()
, and sizeHint()
.
void setMinimumWidth(double width)
minimumWidth()
, setMinimumSize()
, and minimumSize()
.
void setParentLayoutItem(QGraphicsLayoutItemInterface parent)
QGraphicsLayoutItem
to parent. parentLayoutItem()
.
void setPreferredHeight(double height)
preferredHeight()
, preferredWidth()
, setPreferredSize()
, and preferredSize()
.
void setPreferredSize(QSizeF size)
sizeHint()
for Qt::PreferredSize
and provides the default value for effectiveSizeHint()
. In order to unset the preferred size, use an invalid size. preferredSize()
, minimumSize()
, maximumSize()
, Qt::PreferredSize
, and sizeHint()
.
void setPreferredSize(double w, double h)
preferredSize()
, setMaximumSize()
, setMinimumSize()
, and sizeHint()
.
void setPreferredWidth(double width)
preferredWidth()
, preferredHeight()
, setPreferredSize()
, and preferredSize()
.
void setSizePolicy(QSizePolicy.Policy hPolicy, QSizePolicy.Policy vPolicy, QSizePolicy.ControlType controlType)
QSizePolicy
(hPolicy, vPolicy, controlType)). sizePolicy()
, and QWidget::sizePolicy()
.
void setSizePolicy(QSizePolicy policy)
QGraphicsLayoutItem
's default size policy is (QSizePolicy::Fixed
, QSizePolicy::Fixed
, QSizePolicy::DefaultType
), but it is common for subclasses to change the default. For example, QGraphicsWidget
defaults to (QSizePolicy::Preferred
, QSizePolicy::Preferred
, QSizePolicy::DefaultType
).
sizePolicy()
, and QWidget::sizePolicy()
.
QSizePolicy sizePolicy()
setSizePolicy()
, and QWidget::sizePolicy()
.
void setGeometry(QRectF rect)
QGraphicsLayoutItem
to rect, which is in parent coordinates (e.g., the top-left corner of rect is equivalent to the item's position in parent coordinates). Reimplement this function in a subclass of QGraphicsLayoutItem
to enable your item to receive geometry updates.
If rect is outside of the bounds of minimumSize
and maximumSize
, it will be adjusted to its closest size so that it is within the legal bounds.
geometry()
.
QSizeF sizeHint(Qt.SizeHint which, QSizeF constraint)
QGraphicsLayoutItem
, using the width or height of constraint to constrain the output. Reimplement this function in a subclass of QGraphicsLayoutItem
to provide the necessary size hints for your items.
effectiveSizeHint()
.
void updateGeometry()
sizeHint()
function. Subclasses must always call the base implementation when reimplementing this function. effectiveSizeHint()
.
com.trolltech.qt.gui.QMarginsF getContentsMargins()
QGraphicsLayoutItem
. The default implementation assumes all contents margins are 0. The parameters point to values stored in qreals. If any of the pointers is 0, that value will not be updated. QGraphicsWidget::setContentsMargins()
.
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