javax.swing
Class JViewport

java.lang.Object
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  +--java.awt.Component
        |
        +--java.awt.Container
              |
              +--javax.swing.JComponent
                    |
                    +--javax.swing.JViewport

public class JViewport

extends JComponent

implements Accessible

The "viewport" or "porthole" through which you see the underlying information. When you scroll, what moves is the viewport. Its like peering through a camera's viewfinder. Moving the viewfinder upwards brings new things into view at the top of the picture and loses things that were at the bottom.

NOTE:We have implemented a faster scrolling algorithm that does not require a buffer to draw in. The algorithm works as follows:

1. The view and parent view and checked to see if they are JComponents, if they aren't, stop and repaint the whole viewport.
2. If the viewport is obscured by an ancestor, stop and repaint the whole viewport.
3. Compute the region that will become visible, if it is as big as the viewport, stop and repaint the whole view region.
4. Obtain the ancestor Windows graphics and do a copyArea on the scrolled region.
5. Message the view to repaint the newly visible region.
6. The next time paint is invoked on the viewport, if the clip region is smaller than the viewport size a timer is kicked off to repaint the whole region.

In general this approach is much faster. Compared to the backing store approach this avoids the overhead of maintaining an offscreen buffer and having to do two copyAreas. Compared to the non backing store case this approach will greatly reduce the painted region.

This approach can cause slower times than the backing store approach when the viewport is obscured by another window, or partially offscreen. When another window obscures the viewport the copyArea will copy garbage and a paint event will be generated by the system to inform us we need to paint the newly exposed region. The only way to handle this is to repaint the whole viewport, which can cause slower performance than the backing store case. In most applications very rarely will the user be scrolling while the viewport is obscured by another window or offscreen, so this optimization is usually worth the performance hit when obscured.

To turn this behavior on, put the client property "EnableWindowBlit" (a method will added to enable/disable this in the future).

Warning: Serialized objects of this class will not be compatible with future Swing releases. The current serialization support is appropriate for short term storage or RMI between applications running the same version of Swing. A future release of Swing will provide support for long term persistence.

See Also:

JScrollPane, Serialized Form

Inner Class Summary

protected class	JViewport.AccessibleJViewport The class used to obtain the accessible role for this object.
protected class	JViewport.ViewListener A listener for the view.

Inner classes inherited from class javax.swing.JComponent

JComponent.AccessibleJComponent

Field Summary

protected boolean	backingStore True when this viewport is maintaining an offscreen image of its contents, so that some scrolling can take place using fast "bit-blit" operations instead of by accessing the view object to construct the display.
protected Image	backingStoreImage The view image used for a backing store.
protected boolean	isViewSizeSet True when the viewport dimensions have been determined.
protected Point	lastPaintPosition The last viewPosition that we've painted, so we know how much of the backing store image is valid.
protected boolean	scrollUnderway The scrollUnderway flag is used for components like JList.

Fields inherited from class javax.swing.JComponent

accessibleContext, listenerList, TOOL_TIP_TEXT_KEY, ui, UNDEFINED_CONDITION, WHEN_ANCESTOR_OF_FOCUSED_COMPONENT, WHEN_FOCUSED, WHEN_IN_FOCUSED_WINDOW

Fields inherited from class java.awt.Component

BOTTOM_ALIGNMENT, CENTER_ALIGNMENT, LEFT_ALIGNMENT, RIGHT_ALIGNMENT, TOP_ALIGNMENT

Constructor Summary

JViewport()
Create a JViewport

Method Summary

void	addChangeListener(ChangeListener l) Add a ChangeListener to the list that's notified each time the view's size, position, or the viewport's extent size has changed.
protected void	addImpl(Component child, Object constraints, int index) Sets the Viewport's one lightweight child, which can be null.
protected boolean	computeBlit(int dx, int dy, Point blitFrom, Point blitTo, Dimension blitSize, Rectangle blitPaint) Computes the parameters for a blit where the backing store image currently contains oldLoc in the upper left hand corner and we're scrolling to newLoc.
protected LayoutManager	createLayoutManager() Subclassers can override this to install a different layout manager (or null) in the constructor.
protected JViewport.ViewListener	createViewListener() Create a listener for the view.
protected void	firePropertyChange(String propertyName, Object oldValue, Object newValue) Notifies listeners of a property change.
protected void	fireStateChanged()
AccessibleContext	getAccessibleContext() Get the AccessibleContext associated with this JComponent
Dimension	getExtentSize() Returns the size of the visible part of the view in view coordinates.
Insets	getInsets() Returns the insets (border) dimensions as (0,0,0,0), since borders are not supported on a JViewport.
Insets	getInsets(Insets insets) Returns an Insets object containing this JViewport's inset values.
Component	getView() Returns the Viewport's one child or null.
Point	getViewPosition() Returns the view coordinates that appear in the upper left hand corner of the viewport, 0,0 if there's no view.
Rectangle	getViewRect() Return a rectangle whose origin is getViewPosition and size is getExtentSize().
Dimension	getViewSize() If the view's size hasn't been explicitly set, return the preferred size, otherwise return the view's current size.
boolean	isBackingStoreEnabled() Returns true if this viewport is maintaining an offscreen image of its contents.
boolean	isOptimizedDrawingEnabled() The JViewport overrides the default implementation of this method (in JComponent) to return false.
void	paint(Graphics g) Depending on whether the backingStore is enabled, either paint the image through the backing store or paint just the recently exposed part, using the backing store to "blit" the remainder.
protected String	paramString() Returns a string representation of this JViewport.
void	remove(Component child) Removes the Viewport's one lightweight child.
void	removeChangeListener(ChangeListener l) Remove a ChangeListener from the list that's notified each time the views size, position, or the viewports extent size has changed.
void	repaint(long tm, int x, int y, int w, int h) We always repaint in our parent coordinate system to make sure only one paint is performed by the RepaintManager.
void	reshape(int x, int y, int w, int h) Sets the bounds of this viewport.
void	scrollRectToVisible(Rectangle contentRect) Overridden to scroll the view so that Rectangle within the view becomes visible.
void	setBackingStoreEnabled(boolean x) If true if this viewport will maintain an offscreen image of its contents.
void	setBorder(Border border) The viewport "scrolls" it's child (called the "view") by the normal parent/child clipping (typically the view is moved in the opposite direction of the scroll).
void	setExtentSize(Dimension newExtent) Set the size of the visible part of the view using view coordinates.
void	setView(Component view) Sets the Viewport's one lightweight child (view), which can be null.
void	setViewPosition(Point p) Sets the view coordinates that appear in the upper left hand corner of the viewport, does nothing if there's no view.
void	setViewSize(Dimension newSize) Sets the view coordinates that appear in the upper left hand corner of the viewport, and the size of the view.
Dimension	toViewCoordinates(Dimension size) Convert a size in pixel coordinates to view coordinates.
Point	toViewCoordinates(Point p) Convert a point in pixel coordinates to view coordinates.

Methods inherited from class javax.swing.JComponent

addAncestorListener, addNotify, addPropertyChangeListener, addPropertyChangeListener, addVetoableChangeListener, computeVisibleRect, contains, createToolTip, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, fireVetoableChange, getActionForKeyStroke, getAlignmentX, getAlignmentY, getAutoscrolls, getBorder, getBounds, getClientProperty, getComponentGraphics, getConditionForKeyStroke, getDebugGraphicsOptions, getGraphics, getHeight, getLocation, getMaximumSize, getMinimumSize, getNextFocusableComponent, getPreferredSize, getRegisteredKeyStrokes, getRootPane, getSize, getToolTipLocation, getToolTipText, getToolTipText, getTopLevelAncestor, getUIClassID, getVisibleRect, getWidth, getX, getY, grabFocus, hasFocus, isDoubleBuffered, isFocusCycleRoot, isFocusTraversable, isLightweightComponent, isManagingFocus, isOpaque, isPaintingTile, isRequestFocusEnabled, isValidateRoot, paintBorder, paintChildren, paintComponent, paintImmediately, paintImmediately, processComponentKeyEvent, processFocusEvent, processKeyEvent, processMouseMotionEvent, putClientProperty, registerKeyboardAction, registerKeyboardAction, removeAncestorListener, removeNotify, removePropertyChangeListener, removePropertyChangeListener, removeVetoableChangeListener, repaint, requestDefaultFocus, requestFocus, resetKeyboardActions, revalidate, setAlignmentX, setAlignmentY, setAutoscrolls, setBackground, setDebugGraphicsOptions, setDoubleBuffered, setEnabled, setFont, setForeground, setMaximumSize, setMinimumSize, setNextFocusableComponent, setOpaque, setPreferredSize, setRequestFocusEnabled, setToolTipText, setUI, setVisible, unregisterKeyboardAction, update, updateUI

Methods inherited from class java.awt.Container

add, add, add, add, add, addContainerListener, countComponents, deliverEvent, doLayout, findComponentAt, findComponentAt, getComponent, getComponentAt, getComponentAt, getComponentCount, getComponents, getLayout, insets, invalidate, isAncestorOf, layout, list, list, locate, minimumSize, paintComponents, preferredSize, print, printComponents, processContainerEvent, processEvent, remove, removeAll, removeContainerListener, setCursor, setLayout, validate, validateTree

Methods inherited from class java.awt.Component

action, add, addComponentListener, addFocusListener, addInputMethodListener, addKeyListener, addMouseListener, addMouseMotionListener, bounds, checkImage, checkImage, coalesceEvents, contains, createImage, createImage, disable, disableEvents, dispatchEvent, enable, enable, enableEvents, enableInputMethods, getBackground, getBounds, getColorModel, getComponentOrientation, getCursor, getDropTarget, getFont, getFontMetrics, getForeground, getInputContext, getInputMethodRequests, getLocale, getLocation, getLocationOnScreen, getName, getParent, getPeer, getSize, getToolkit, getTreeLock, gotFocus, handleEvent, hide, imageUpdate, inside, isDisplayable, isEnabled, isLightweight, isShowing, isValid, isVisible, keyDown, keyUp, list, list, list, location, lostFocus, mouseDown, mouseDrag, mouseEnter, mouseExit, mouseMove, mouseUp, move, nextFocus, paintAll, postEvent, prepareImage, prepareImage, printAll, processComponentEvent, processInputMethodEvent, processMouseEvent, remove, removeComponentListener, removeFocusListener, removeInputMethodListener, removeKeyListener, removeMouseListener, removeMouseMotionListener, repaint, repaint, repaint, resize, resize, setBounds, setBounds, setComponentOrientation, setDropTarget, setLocale, setLocation, setLocation, setName, setSize, setSize, show, show, size, toString, transferFocus

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

isViewSizeSet

protected boolean isViewSizeSet

True when the viewport dimensions have been determined.

lastPaintPosition

protected Point lastPaintPosition

The last viewPosition that we've painted, so we know how much of the backing store image is valid.

backingStore

protected boolean backingStore

True when this viewport is maintaining an offscreen image of its contents, so that some scrolling can take place using fast "bit-blit" operations instead of by accessing the view object to construct the display.

backingStoreImage

protected transient Image backingStoreImage

The view image used for a backing store.

scrollUnderway

protected boolean scrollUnderway

The scrollUnderway flag is used for components like JList. When the downarrow key is pressed on a JList and the selected cell is the last in the list, the scrollpane autoscrolls. Here, the old selected cell needs repainting and so we need a flag to make the viewport do the optimised painting only when there is an explicit call to setViewPosition(Point). When setBounds() is called through other routes, the flag is off and the view repaints normally. Another approach would be to remove this from the Viewport class and have the JList manage this case by using setBackingStoreEnabled().

Constructor Detail

JViewport

public JViewport()

Create a JViewport

Method Detail

addImpl

protected void addImpl(Component child,
                       Object constraints,
                       int index)

Sets the Viewport's one lightweight child, which can be null. (Since there is only one child which occupies the entire viewport, the constraints and index arguments are ignored.)

Overrides:

addImpl in class Container

Parameters:

child - the Component ______________

constraints - the Object ______________

index - the int ______________

See Also:

setView(java.awt.Component)

remove

public void remove(Component child)

Removes the Viewport's one lightweight child.

Overrides:

remove in class Container

See Also:

setView(java.awt.Component)

scrollRectToVisible

public void scrollRectToVisible(Rectangle contentRect)

Overridden to scroll the view so that Rectangle within the view becomes visible.

Overrides:

scrollRectToVisible in class JComponent

Parameters:

contentRect - the Rectangle to display

setBorder

public final void setBorder(Border border)

The viewport "scrolls" it's child (called the "view") by the normal parent/child clipping (typically the view is moved in the opposite direction of the scroll). A non-null border, or non-zero insets, isn't supported, to prevent the geometry of this component from becoming complex enough to inhibit subclassing. To create a JViewport with a border, add it to a JPanel that has a border.

Overrides:

setBorder in class JComponent

Parameters:

border - the Border to set

getInsets

public final Insets getInsets()

Returns the insets (border) dimensions as (0,0,0,0), since borders are not supported on a JViewport.

Overrides:

getInsets in class JComponent

Returns:

new Insets(0, 0, 0, 0)

See Also:

setBorder(javax.swing.border.Border)

getInsets

public final Insets getInsets(Insets insets)

Returns an Insets object containing this JViewport's inset values. The passed-in Insets object will be reinitialized, and all existing values within this object are overwritten.

Overrides:

getInsets in class JComponent

Parameters:

insets - the Insets object which can be reused.

See Also:

getInsets()

isOptimizedDrawingEnabled

public boolean isOptimizedDrawingEnabled()

The JViewport overrides the default implementation of this method (in JComponent) to return false. This ensures that the drawing machinery will call the Viewport's paint() implementation rather than messaging the JViewport's children directly.

Overrides:

isOptimizedDrawingEnabled in class JComponent

Returns:

false

paint

public void paint(Graphics g)

Depending on whether the backingStore is enabled, either paint the image through the backing store or paint just the recently exposed part, using the backing store to "blit" the remainder.

The term "blit" is the pronounced version of the PDP-10 BLT (BLock Transfer) instruction, which copied a block of bits. (In case you were curious.)

Overrides:

paint in class JComponent

Parameters:

g - the Graphics context within which to paint

reshape

public void reshape(int x,
                    int y,
                    int w,
                    int h)

Sets the bounds of this viewport. If the viewports width or height has changed, fire a StateChanged event.

Overrides:

reshape in class JComponent

Parameters:

x - left edge of the origin

y - top edge of the origin

w - width in pixels

h - height in pixels

See Also:

JComponent.reshape(int, int, int, int)

isBackingStoreEnabled

public boolean isBackingStoreEnabled()

Returns true if this viewport is maintaining an offscreen image of its contents.

setBackingStoreEnabled

public void setBackingStoreEnabled(boolean x)

If true if this viewport will maintain an offscreen image of its contents. The image is used to reduce the cost of small one dimensional changes to the viewPosition. Rather than repainting the entire viewport we use Graphics.copyArea() to effect some of the scroll.

getView

public Component getView()

Returns the Viewport's one child or null.

See Also:

setView(java.awt.Component)

setView

public void setView(Component view)

Sets the Viewport's one lightweight child (view), which can be null.

See Also:

getView()

getViewSize

public Dimension getViewSize()

If the view's size hasn't been explicitly set, return the preferred size, otherwise return the view's current size. If there is no view, return 0,0.

Returns:

a Dimension object specifying the size of the view

setViewSize

public void setViewSize(Dimension newSize)

Sets the view coordinates that appear in the upper left hand corner of the viewport, and the size of the view.

Parameters:

newSize - a Dimension object specifying the size and location of the new view coordinates, or null if there is no view

getViewPosition

public Point getViewPosition()

Returns the view coordinates that appear in the upper left hand corner of the viewport, 0,0 if there's no view.

Returns:

a Point object giving the upper left coordinates

setViewPosition

public void setViewPosition(Point p)

Sets the view coordinates that appear in the upper left hand corner of the viewport, does nothing if there's no view.

Parameters:

p - a Point object giving the upper left coordinates

getViewRect

public Rectangle getViewRect()

Return a rectangle whose origin is getViewPosition and size is getExtentSize(). This is the visible part of the view, in view coordinates.

Returns:

a Rectangle giving the visible part of the view using view coordinates.

computeBlit

protected boolean computeBlit(int dx,
                              int dy,
                              Point blitFrom,
                              Point blitTo,
                              Dimension blitSize,
                              Rectangle blitPaint)

Computes the parameters for a blit where the backing store image currently contains oldLoc in the upper left hand corner and we're scrolling to newLoc. The parameters are modified to return the values required for the blit.

getExtentSize

public Dimension getExtentSize()

Returns the size of the visible part of the view in view coordinates.

Returns:

a Dimension object giving the size of the view

toViewCoordinates

public Dimension toViewCoordinates(Dimension size)

Convert a size in pixel coordinates to view coordinates. Subclasses of viewport that support "logical coordinates" will override this method.

Parameters:

size - a Dimension object using pixel coordinates

Returns:

a Dimension object converted to view coordinates

toViewCoordinates

public Point toViewCoordinates(Point p)

Convert a point in pixel coordinates to view coordinates. Subclasses of viewport that support "logical coordinates" will override this method.

Parameters:

p - a Point object using pixel coordinates

Returns:

a Point object converted to view coordinates

setExtentSize

public void setExtentSize(Dimension newExtent)

Set the size of the visible part of the view using view coordinates.

Parameters:

newExtent - a Dimension object specifying the size of the view

createViewListener

protected JViewport.ViewListener createViewListener()

Create a listener for the view.

Returns:

a ViewListener

createLayoutManager

protected LayoutManager createLayoutManager()

Subclassers can override this to install a different layout manager (or null) in the constructor. Returns a new JViewportLayout object.

Returns:

a LayoutManager

addChangeListener

public void addChangeListener(ChangeListener l)

Add a ChangeListener to the list that's notified each time the view's size, position, or the viewport's extent size has changed.

Parameters:

l - the ChangeListener to add

See Also:

removeChangeListener(javax.swing.event.ChangeListener), setViewPosition(java.awt.Point), setViewSize(java.awt.Dimension), setExtentSize(java.awt.Dimension)

removeChangeListener

public void removeChangeListener(ChangeListener l)

Remove a ChangeListener from the list that's notified each time the views size, position, or the viewports extent size has changed.

Parameters:

l - the ChangeListener to remove

See Also:

addChangeListener(javax.swing.event.ChangeListener)

fireStateChanged

protected void fireStateChanged()

repaint

public void repaint(long tm,
                    int x,
                    int y,
                    int w,
                    int h)

We always repaint in our parent coordinate system to make sure only one paint is performed by the RepaintManager.

Overrides:

repaint in class JComponent

Parameters:

tm - maximum time in milliseconds before update

x - the x coordinate (pixels over from left)

y - the y coordinate (pixels down from top)

width - the width

height - the height

See Also:

Component.update(java.awt.Graphics)

paramString

protected String paramString()

Returns a string representation of this JViewport. This method is intended to be used only for debugging purposes, and the content and format of the returned string may vary between implementations. The returned string may be empty but may not be null.

Overrides:

paramString in class JComponent

Returns:

a string representation of this JViewport.

firePropertyChange

protected void firePropertyChange(String propertyName,
                                  Object oldValue,
                                  Object newValue)

Notifies listeners of a property change. This is subclassed to update the windowBlit ivar (putClientProperty is final).

Overrides:

firePropertyChange in class JComponent

Tags copied from class: JComponent

Parameters:

propertyName - The programmatic name of the property that was changed.

oldValue - The old value of the property.

newValue - The new value of the property.

See Also:

PropertyChangeSupport

getAccessibleContext

public AccessibleContext getAccessibleContext()

Get the AccessibleContext associated with this JComponent

Specified by:

getAccessibleContext in interface Accessible

Overrides:

getAccessibleContext in class JComponent

Returns:

the AccessibleContext of this JComponent