Wt  4.11.0
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Public Member Functions | Protected Member Functions | List of all members
Wt::WImage Class Reference

A widget that displays an image. More...

#include <Wt/WImage.h>

Inheritance diagram for Wt::WImage:
[legend]

Public Member Functions

 WImage ()
 Creates an empty image widget.
 
 WImage (const WLink &imageLink)
 Creates an image widget with a given image link.
 
 WImage (const WLink &imageLink, const WString &altText)
 Creates an image widget with a given image link and alternate text.
 
void setAlternateText (const WString &text)
 Sets an alternate text.
 
const WStringalternateText () const
 Returns the alternate text.
 
void setImageLink (const WLink &link)
 Sets the image link.
 
const WLinkimageLink () const
 Returns the image link.
 
void addArea (std::unique_ptr< WAbstractArea > area)
 Adds an interactive area.
 
template<typename Area >
AreaaddArea (std::unique_ptr< Area > area)
 Adds an interactive area, returning a raw pointer.
 
void insertArea (int index, std::unique_ptr< WAbstractArea > area)
 Inserts an interactive area.
 
template<typename Area >
AreainsertArea (int index, std::unique_ptr< Area > area)
 Inserts an interactive area, returning a raw pointer.
 
std::unique_ptr< WAbstractArearemoveArea (WAbstractArea *area)
 Removes an interactive area.
 
WAbstractAreaarea (int index) const
 Returns the interactive area at the given index.
 
const std::vector< WAbstractArea * > areas () const
 Returns the interactive areas set for this widget.
 
EventSignalimageLoaded ()
 Event emitted when the image was loaded.
 
- Public Member Functions inherited from Wt::WInteractWidget
 WInteractWidget ()
 Create an InteractWidget.
 
EventSignal< WKeyEvent > & keyWentDown ()
 Event signal emitted when a keyboard key is pushed down.
 
EventSignal< WKeyEvent > & keyPressed ()
 Event signal emitted when a "character" was entered.
 
EventSignal< WKeyEvent > & keyWentUp ()
 Event signal emitted when a keyboard key is released.
 
EventSignalenterPressed ()
 Event signal emitted when enter was pressed.
 
EventSignalescapePressed ()
 Event signal emitted when escape was pressed.
 
EventSignal< WMouseEvent > & clicked ()
 Event signal emitted when the primary mouse button was clicked on this widget.
 
EventSignal< WMouseEvent > & doubleClicked ()
 Event signal emitted when the primary mouse button was double clicked on this widget.
 
EventSignal< WMouseEvent > & mouseWentDown ()
 Event signal emitted when a mouse button was pushed down on this widget.
 
EventSignal< WMouseEvent > & mouseWentUp ()
 Event signal emitted when a mouse button was released on this widget.
 
EventSignal< WMouseEvent > & mouseWentOut ()
 Event signal emitted when the mouse went out of this widget.
 
EventSignal< WMouseEvent > & mouseWentOver ()
 Event signal emitted when the mouse entered this widget.
 
EventSignal< WMouseEvent > & mouseMoved ()
 Event signal emitted when the mouse moved over this widget.
 
EventSignal< WMouseEvent > & mouseDragged ()
 Event signal emitted when the mouse is dragged over this widget.
 
EventSignal< WMouseEvent > & mouseWheel ()
 Event signal emitted when the mouse scroll wheel was used.
 
EventSignal< WTouchEvent > & touchStarted ()
 Event signal emitted when a finger is placed on the screen.
 
EventSignal< WTouchEvent > & touchEnded ()
 Event signal emitted when a finger is removed from the screen.
 
EventSignal< WTouchEvent > & touchMoved ()
 Event signal emitted when a finger, which is already placed on the screen, is moved across the screen.
 
EventSignal< WGestureEvent > & gestureStarted ()
 Event signal emitted when a gesture is started.
 
EventSignal< WGestureEvent > & gestureChanged ()
 Event signal emitted when a gesture is changed.
 
EventSignal< WGestureEvent > & gestureEnded ()
 Event signal emitted when a gesture is ended.
 
void setDraggable (const std::string &mimeType, WWidget *dragWidget=nullptr, bool isDragWidgetOnly=false, WObject *sourceWidget=nullptr)
 Configure dragging for drag and drop.
 
void unsetDraggable ()
 Disable drag & drop for this widget.
 
void setMouseOverDelay (int delay)
 Sets a delay for the mouse over event.
 
int mouseOverDelay () const
 Returns the mouse over signal delay.
 
virtual void setPopup (bool popup) override
 Lets the widget overlay over other sibling widgets.
 
virtual void load () override
 Loads content just before the widget is used.
 
virtual bool isEnabled () const override
 Returns whether the widget is enabled.
 
- Public Member Functions inherited from Wt::WWebWidget
 WWebWidget ()
 Construct a WebWidget.
 
virtual std::vector< WWidget * > children () const override
 Returns child widgets.
 
SignalchildrenChanged ()
 Signal emitted when children have been added or removed.
 
virtual void setPositionScheme (PositionScheme scheme) override
 Sets the CSS position scheme.
 
virtual PositionScheme positionScheme () const override
 Returns the CSS position scheme.
 
virtual void setOffsets (const WLength &offset, WFlags< Side > sides=AllSides) override
 Sets CSS offsets for a non-statically positioned widget.
 
virtual WLength offset (Side s) const override
 Returns a CSS offset.
 
virtual void resize (const WLength &width, const WLength &height) override
 Resizes the widget.
 
virtual WLength width () const override
 Returns the width.
 
virtual WLength height () const override
 Returns the height.
 
virtual void setMinimumSize (const WLength &width, const WLength &height) override
 Sets a minimum size.
 
virtual WLength minimumWidth () const override
 Returns the minimum width.
 
virtual WLength minimumHeight () const override
 Returns the minimum height.
 
virtual void setMaximumSize (const WLength &width, const WLength &height) override
 Sets a maximum size.
 
virtual WLength maximumWidth () const override
 Returns the maximum width.
 
virtual WLength maximumHeight () const override
 Returns the maximum height.
 
virtual void setLineHeight (const WLength &height) override
 Sets the CSS line height for contained text.
 
virtual WLength lineHeight () const override
 Returns the CSS line height for contained text.
 
virtual void setFloatSide (Side s) override
 Specifies a CSS float side.
 
virtual Side floatSide () const override
 Returns the CSS float side.
 
virtual void setClearSides (WFlags< Side > sides) override
 Sets the sides that should be cleared of floats.
 
virtual WFlags< SideclearSides () const override
 Returns the sides that should remain empty.
 
virtual void setMargin (const WLength &margin, WFlags< Side > sides=AllSides) override
 Sets CSS margins around the widget.
 
virtual WLength margin (Side side) const override
 Returns a CSS margin set.
 
virtual void setHiddenKeepsGeometry (bool enabled) override
 Sets whether the widget keeps its geometry when hidden.
 
virtual bool hiddenKeepsGeometry () const override
 Returns whether the widget keeps its geometry when hidden.
 
virtual void setHidden (bool hidden, const WAnimation &animation=WAnimation()) override
 Hides or shows the widget.
 
virtual bool isHidden () const override
 Returns whether the widget is set hidden.
 
virtual bool isVisible () const override
 Returns whether the widget is visible.
 
virtual void setDisabled (bool disabled) override
 Sets whether the widget is disabled.
 
virtual bool isDisabled () const override
 Returns whether the widget is set disabled.
 
virtual bool isPopup () const override
 Returns whether the widget is overlayed.
 
virtual void setInline (bool isInline) override
 Sets whether the widget is displayed inline or as a block.
 
virtual bool isInline () const override
 Returns whether the widget is displayed inline or as block.
 
virtual void setDecorationStyle (const WCssDecorationStyle &style) override
 Sets a CSS decoration style.
 
virtual WCssDecorationStyledecorationStyle () override
 Returns the decoration style of this widget.
 
virtual void setStyleClass (const WString &styleClass) override
 Sets (one or more) CSS style classes.
 
virtual WString styleClass () const override
 Returns the CSS style class.
 
virtual void addStyleClass (const WString &styleClass, bool force=false) override
 Adds a CSS style class.
 
virtual void removeStyleClass (const WString &styleClass, bool force=false) override
 Removes a CSS style class.
 
virtual bool hasStyleClass (const WString &styleClass) const override
 Returns whether the widget has a style class.
 
virtual void setVerticalAlignment (AlignmentFlag alignment, const WLength &length=WLength()) override
 Sets the vertical alignment.
 
virtual AlignmentFlag verticalAlignment () const override
 Returns the vertical alignment.
 
virtual WLength verticalAlignmentLength () const override
 Returns the fixed vertical alignment that was set.
 
virtual void setToolTip (const WString &text, TextFormat textFormat=TextFormat::Plain) override
 Sets a tooltip.
 
virtual void setDeferredToolTip (bool enable, TextFormat textFormat=TextFormat::Plain) override
 Enable deferred tooltip.
 
virtual WString toolTip () const override
 Returns the tooltip.
 
virtual void refresh () override
 Refresh the widget.
 
virtual void setAttributeValue (const std::string &name, const WString &value) override
 Sets an attribute value.
 
virtual WString attributeValue (const std::string &name) const override
 Returns an attribute value.
 
virtual void setJavaScriptMember (const std::string &name, const std::string &value) override
 Sets a JavaScript member.
 
virtual std::string javaScriptMember (const std::string &name) const override
 Returns the value of a JavaScript member.
 
virtual void callJavaScriptMember (const std::string &name, const std::string &args) override
 Calls a JavaScript member.
 
virtual bool loaded () const override
 Returns whether this widget has been loaded.
 
virtual void setId (const std::string &id) override
 Sets the CSS Id.
 
virtual WWidgetfind (const std::string &name) override
 Finds a descendent widget by name.
 
virtual WWidgetfindById (const std::string &id) override
 Finds a descendent widget by id.
 
virtual void setSelectable (bool selectable) override
 Sets as selectable.
 
virtual void doJavaScript (const std::string &javascript) override
 Executes the given JavaScript statements when the widget is rendered or updated.
 
virtual const std::string id () const override
 Returns the (unique) identifier for this object.
 
void setLoadLaterWhenInvisible (bool)
 Change the way the widget is loaded when invisible.
 
std::string htmlTagName () const
 returns the current html tag name
 
void setHtmlTagName (const std::string &tag)
 set the custom HTML tag name
 
virtual void setCanReceiveFocus (bool enabled) override
 Sets whether the widget can receive focus.
 
virtual bool canReceiveFocus () const override
 Returns whether the widget can receive focus.
 
virtual bool setFirstFocus () override
 Set focus on the widget's first descendant.
 
virtual void setFocus (bool focus) override
 Sets focus.
 
virtual bool hasFocus () const override
 Returns whether the widget currently has the focus.
 
virtual void setTabIndex (int index) override
 Sets the tab index.
 
virtual int tabIndex () const override
 Returns the tab index.
 
EventSignalblurred ()
 Signal emitted when the widget lost focus.
 
EventSignalfocussed ()
 Signal emitted when the widget recieved focus.
 
virtual bool scrollVisibilityEnabled () const final override
 Returns whether scroll visibility detection is enabled for this widget.
 
virtual void setScrollVisibilityEnabled (bool enabled) final override
 Sets whether scroll visibility detection is enabled for this widget.
 
virtual int scrollVisibilityMargin () const final override
 Returns the margin around the viewport within which the widget is considered visible.
 
virtual void setScrollVisibilityMargin (int margin) final override
 Sets the margin around the viewport within which the widget is considered visible.
 
virtual Signal< bool > & scrollVisibilityChanged () final override
 Signal triggered when the scroll visibility of this widget changes.
 
virtual bool isScrollVisible () const final override
 Returns whether this widget is currently considered scroll visible.
 
virtual void setThemeStyleEnabled (bool enabled) final override
 Sets whether theme styling for a widget is enabled or disabled.
 
virtual bool isThemeStyleEnabled () const final override
 Returns whether this widget is currently styled by the chosen theme.
 
virtual void setObjectName (const std::string &name) override
 Sets an object name.
 
void setFocus ()
 Sets focus.
 
virtual void setFocus (bool focus)=0
 Sets focus.
 
- Public Member Functions inherited from Wt::WWidget
virtual ~WWidget ()
 Destructor.
 
WWidgetparent () const
 Returns the parent widget.
 
virtual std::unique_ptr< WWidgetremoveWidget (WWidget *widget)
 Removes a child widget.
 
template<typename Widget >
std::unique_ptr< Widget > removeWidget (Widget *widget)
 Removes a child widget.
 
std::unique_ptr< WWidgetremoveFromParent ()
 Removes the widget from its parent.
 
void setWidth (const WLength &width)
 Sets the width.
 
void setHeight (const WLength &height)
 Sets the height.
 
virtual void positionAt (const WWidget *widget, Orientation orientation=Orientation::Vertical)
 Positions a widget next to another widget.
 
virtual void toggleStyleClass (const WString &styleClass, bool add, bool force=false)
 Toggles a CSS style class.
 
std::string jsRef () const
 Returns a JavaScript expression to the corresponding DOM node.
 
void setFocus ()
 Sets focus.
 
virtual void acceptDrops (const std::string &mimeType, const WString &hoverStyleClass=WString())
 Sets a mime type to be accepted for dropping.
 
virtual void stopAcceptDrops (const std::string &mimeType)
 Indicates that a mime type is no longer accepted for dropping.
 
virtual void htmlText (std::ostream &out)
 Streams the (X)HTML representation.
 
bool isRendered () const
 Returns whether the widget is rendered.
 
void hide ()
 Hides the widget.
 
void animateHide (const WAnimation &animation)
 Hides the widget using an animation.
 
void show ()
 Shows the widget.
 
void animateShow (const WAnimation &animation)
 Shows the widget using an animation.
 
void enable ()
 Enables the widget.
 
void disable ()
 Disable thes widget.
 
bool layoutSizeAware () const
 Returns whether the widget is layout size aware.
 
- Public Member Functions inherited from Wt::WObject
void addChild (std::unique_ptr< WObject > child)
 Add a child WObject whose lifetime is determined by this WObject.
 
template<typename Child >
ChildaddChild (std::unique_ptr< Child > child)
 Add a child WObject, returning a raw pointer.
 
std::unique_ptr< WObjectremoveChild (WObject *child)
 Remove a child WObject, so its lifetime is no longer determined by this WObject.
 
template<typename Child >
std::unique_ptr< ChildremoveChild (Child *child)
 Remove a child WObject, so its lifetime is no longer determined by this WObject.
 
virtual std::string objectName () const
 Returns the object name.
 
void resetLearnedSlots ()
 Resets learned stateless slot implementations.
 
template<class T >
void resetLearnedSlot (void(T::*method)())
 Resets a learned stateless slot implementation.
 
template<class T >
WStatelessSlot * implementStateless (void(T::*method)())
 Declares a slot to be stateless and learn client-side behaviour on first invocation.
 
template<class T >
WStatelessSlot * implementStateless (void(T::*method)(), void(T::*undoMethod)())
 Declares a slot to be stateless and learn client-side behaviour in advance.
 
void isNotStateless ()
 Marks the current function as not stateless.
 
template<class T >
WStatelessSlot * implementJavaScript (void(T::*method)(), const std::string &jsCode)
 Provides a JavaScript implementation for a method.
 
- Public Member Functions inherited from Wt::Core::observable
 observable () noexcept
 Default constructor.
 
virtual ~observable ()
 Destructor.
 
template<typename... Args, typename C >
auto bindSafe (void(C::*method)(Args...)) noexcept
 Protects a method call against object destruction.
 
template<typename... Args, typename C >
auto bindSafe (void(C::*method)(Args...) const) const noexcept
 Protects a const method call against object destruction.
 
template<typename Function >
auto bindSafe (const Function &function) noexcept
 Protects a function against object destruction.
 

Protected Member Functions

virtual void render (WFlags< RenderFlag > flags) override
 Renders the widget.
 
- Protected Member Functions inherited from Wt::WInteractWidget
virtual void propagateSetEnabled (bool enabled) override
 Propagates that a widget was enabled or disabled through children.
 
- Protected Member Functions inherited from Wt::WWebWidget
virtual void enableAjax () override
 Progresses to an Ajax-enabled widget.
 
virtual WStatelessSlot * getStateless (Method method) override
 On-demand stateless slot implementation.
 
- Protected Member Functions inherited from Wt::WWidget
void setLayoutSizeAware (bool sizeAware)
 Sets the widget to be aware of its size set by a layout manager.
 
virtual void layoutSizeChanged (int width, int height)
 Virtual method that indicates a size change.
 
 WWidget ()
 Creates a widget.
 
virtual void dropEvent (WDropEvent dropEvent)
 Handles a drop event.
 
virtual int boxPadding (Orientation orientation) const
 Returns the widget's built-in padding.
 
virtual int boxBorder (Orientation orientation) const
 Returns the widget's built-in border width.
 
void scheduleRender (WFlags< RepaintFlag > flags=None)
 Schedules rerendering of the widget.
 

Additional Inherited Members

- Public Types inherited from Wt::WObject
typedef void(WObject::* Method) ()
 Typedef for a WObject method without arguments.
 
- Static Public Member Functions inherited from Wt::WWebWidget
static std::string jsStringLiteral (const std::string &v, char delimiter='\'')
 Turn a CharEncoding::UTF8 encoded string into a JavaScript string literal.
 
- Static Public Member Functions inherited from Wt::WWidget
static WString tr (const char *key)
 Short hand for WString::tr()
 

Detailed Description

A widget that displays an image.

The image may be specified either as a URL, or may be dynamically generated by a WResource.

You may listen to events by attaching event listeners to signals such as clicked(). Since mouse events pass the coordinates through a WMouseEvent object, it is possible to react to clicks in specific parts of the image. An alternative is to define interactive areas on the image using addArea(), which in addition allows to have customized tool tips for certain image areas (using WAbstractArea::setToolTip()).

Usage example:

Wt::WImage *img = addWidget(std::make_unique<Wt::WImage>("images/johnny_cash.png"));
img->setAlternateText("Johnny Cash sings a song");
A signal that conveys user-interface events.
Definition WSignal.h:558
A widget that displays an image.
Definition WImage.h:54

WImage is an inline widget.

CSS

The widget corresponds to the HTML <img> tag and does not provide styling. It can be styled using inline or external CSS as appropriate.

See also
WResource, WPaintedWidget

Constructor & Destructor Documentation

◆ WImage() [1/2]

Wt::WImage::WImage ( const WLink imageLink)

Creates an image widget with a given image link.

The imageLink may link to a URL or resource.

◆ WImage() [2/2]

Wt::WImage::WImage ( const WLink imageLink,
const WString altText 
)

Creates an image widget with a given image link and alternate text.

The imageLink may link to a URL or resource.

Member Function Documentation

◆ addArea() [1/2]

template<typename Area >
Area * Wt::WImage::addArea ( std::unique_ptr< Area area)

Adds an interactive area, returning a raw pointer.

This is implemented as:

Area *result = area.get();
addArea(std::unique_ptr<WAbstractArea>(std::move(area)));
return result;
void addArea(std::unique_ptr< WAbstractArea > area)
Adds an interactive area.
Definition WImage.C:144
WAbstractArea * area(int index) const
Returns the interactive area at the given index.
Definition WImage.C:161

◆ addArea() [2/2]

void Wt::WImage::addArea ( std::unique_ptr< WAbstractArea area)

Adds an interactive area.

Adds the area which listens to events in a specific region of the image. Areas are organized in an indexed list, to which the given area is appended. When areas overlap, the area with the lowest index receives the event.

Ownership of the area is transferred to the image.

See also
insertArea(int, WAbstractArea *)
Note
Currently it is not possible to add a first area after the image has been rendered. If you want to use interactive areas you need to add one immediately.

◆ alternateText()

const WString & Wt::WImage::alternateText ( ) const

Returns the alternate text.

See also
setAlternateText()

◆ area()

WAbstractArea * Wt::WImage::area ( int  index) const

Returns the interactive area at the given index.

Returns 0 if index was invalid.

See also
insertArea(int, WAbstractArea *)

◆ areas()

const std::vector< WAbstractArea * > Wt::WImage::areas ( ) const

Returns the interactive areas set for this widget.

See also
addArea()

◆ imageLink()

const WLink & Wt::WImage::imageLink ( ) const

Returns the image link.

See also
setLink()

◆ insertArea() [1/2]

template<typename Area >
Area * Wt::WImage::insertArea ( int  index,
std::unique_ptr< Area area 
)

Inserts an interactive area, returning a raw pointer.

This is implemented as:

Area *result = area.get();
insertArea(index, std::unique_ptr<WAbstractArea>(std::move(area)));
return result;
void insertArea(int index, std::unique_ptr< WAbstractArea > area)
Inserts an interactive area.
Definition WImage.C:149

◆ insertArea() [2/2]

void Wt::WImage::insertArea ( int  index,
std::unique_ptr< WAbstractArea area 
)

Inserts an interactive area.

Inserts the area which listens to events in the coresponding area of the image. Areas are organized in a list, and the area is inserted at index index. When areas overlap, the area with the lowest index receives the event.

Ownership of the area is transferred to the image.

See also
addArea(std::unique_ptr<WAbstractArea>);
Note
Currently it is not possible to add a first area after the image has been rendered. If you want to use interactive areas you need to add one immediately.

◆ removeArea()

std::unique_ptr< WAbstractArea > Wt::WImage::removeArea ( WAbstractArea area)

Removes an interactive area.

Removes the area from this widget.

See also
addArea(WAbstractArea *)

◆ render()

void Wt::WImage::render ( WFlags< RenderFlag flags)
overrideprotectedvirtual

Renders the widget.

This function renders the widget (or an update for the widget), after this has been scheduled using scheduleRender().

The default implementation will render the widget by serializing changes to JavaScript and HTML. You may want to reimplement this widget if you have been postponing some of the layout / rendering implementation until the latest moment possible. In that case you should make sure you call the base implementation however.

Reimplemented from Wt::WWebWidget.

◆ setAlternateText()

void Wt::WImage::setAlternateText ( const WString text)

Sets an alternate text.

The alternate text should provide a fallback for browsers that do not display an image. If no sensible fallback text can be provided, an empty text is preferred over nonsense.

This should not be confused with toolTip() text, which provides additional information that is displayed when the mouse hovers over the image.

The default alternate text is an empty text ("").

See also
alternateText()

◆ setImageLink()

void Wt::WImage::setImageLink ( const WLink link)

Sets the image link.

The image may be specified as a URL or as a resource. A resource specifies application-dependent content, which may be used to generate an image on demand.