javax.swing.text
Class View

java.lang.Object
  |
  +--javax.swing.text.View

Direct Known Subclasses:

ComponentView, CompositeView, IconView, LabelView, PlainView

public abstract class View

extends Object

implements SwingConstants

A very important part of the text package is the View class. As the name suggests it represents a view of the text model, or a piece of the text model. It is this class that is responsible for the look of the text component. The view is not intended to be some completely new thing that one must learn, but rather is much like a lightweight component. In fact, the original View implementation was a lightweight component. There were several reasons why the Component implementation was abandoned in favor of an alternative.

1. There was barely had time to get the lightweight component support in the 1.1 version of the JDK. There simply wasn't time to lighten up the component further to where it would need to be to be used for text purposes. The additions made to JComponent increased the memory consumption, and as it currently stands it's much too heavy for representing text.

2. The layout semantics aren't quite right for text, and changing the current layout semantics of component might break existing applications.

3. The component api uses integers, but in 1.2 one can use floating point device independent coordinates. An api that works in both 1.1 and 1.2 would be convenient for minimizing transition difficulties. The View class uses the Shape interface and float arguments to enable View implementations in JDK 1.2 and later while still functioning in the older 1.1 JDK.

By default, a view is very light. It contains a reference to the parent view from which it can fetch many things without holding state, and it contains a reference to a portion of the model (Element). A view does not have to exactly represent an element in the model, that is simply a typical and therefore convenient mapping. A view can alternatively maintain a couple of Position objects to maintain it's location in the model (i.e. represent a fragment of an element). This is typically the result of formatting where views have been broken down into pieces. The convenience of a substantial relationship to the element makes it easier to build factories to produce the views, and makes it easier to keep track of the view pieces as the model is changed and the view must be changed to reflect the model. Simple views therefore represent an Element directly and complex views do not.

A view has the following responsibilities:

Participate in layout.

The view has a setSize method which is like doLayout and setSize in Component combined. The view has a preferenceChanged method which is like invalidate in Component except that one can invalidate just one axis and the child requesting the change is identified.

A View expresses the size that it would like to be in terms of three values, a minimum, a preferred, and a maximum span. Layout in a view is can be done independantly upon each axis. For a properly functioning View implementation, the minimum span will be <= the preferred span which in turn will be <= the maximum span.

The minimum set of methods for layout are:

• getMinimumSpan
• getPreferredSpan
• getMaximumSpan
• getAlignment
• preferenceChanged
• setSize

The setSize method should be prepared to be called a number of times (i.e. It may be called even if the size didn't change). The setSize method is generally called to make sure the View layout is complete prior to trying to perform an operation on it that requires an up-to-date layout. A views size should always be set to a value within the minimum and maximum span specified by that view. Additionally, the view must always call the preferenceChanged method on the parent if it has changed the values for the layout it would like, and expects the parent to honor. The parent View is not required to recognize a change until the preferenceChanged has been sent. This allows parent View implementations to cache the child requirements if desired. The calling sequence looks something like the following:

The exact calling sequence is up to the layout functionality of the parent view (if the view has any children). The view may collect the preferences of the children prior to determining what it will give each child, or it might iteratively update the children one at a time.

Render a portion of the model.

This is done in the paint method, which is pretty much like a component paint method. Views are expected to potentially populate a fairly large tree. A View has the following semantics for rendering:

• The view gets it's allocation from the parent at paint time, so it must be prepared to redo layout if the allocated area is different from what it is prepared to deal with.
• The coordinate system is the same as the hosting Component (i.e. the Component returned by the getContainer method). This means a child view lives in the same coordinate system as the parent view unless the parent has explicitly changed the coordinate system. To schedule itself to be repainted a view can call repaint on the hosting Component.
• The default is to not clip the children. It is more effecient to allow a view to clip only if it really feels it needs clipping.
• The Graphics object given is not initialized in any way. A view should set any settings needed.
• A View is inherently transparent. While a view may render into it's entire allocation, typically a view does not. Rendering is performed by tranversing down the tree of View implementations. Each View is responsible for rendering it's children. This behavior is depended upon for thread safety. While view implementations do not necessarily have to be implemented with thread safety in mind, other view implementations that do make use of concurrency can depend upon a tree traversal to guarantee thread safety.
• The order of views relative to the model is up to the implementation. Although child views will typically be arranged in the same order that they occur in the model, they may be visually arranged in an entirely different order. View implementations may have Z-Order associated with them if the children are overlapping.

The methods for rendering are:

• paint

Translate between the model and view coordinate systems.

Because the view objects are produced from a factory and therefore cannot necessarily be counted upon to be in a particular pattern, one must be able to perform translation to properly locate spatial representation of the model. The methods for doing this are:

• modelToView
• viewToModel
• getDocument
• getElement
• getStartOffset
• getEndOffset

The layout must be valid prior to attempting to make the translation. The translation is not valid, and must not be attempted while changes are being broadcasted from the model via a DocumentEvent.

Respond to changes from the model.

If the overall view is represented by many pieces (which is the best situation if one want to be able to change the view and write the least amount of new code), it would be impractical to have a huge number of DocumentListeners. If each view listened to the model, only a few would actually be interested in the changes broadcasted at any given time. Since the model has no knowledge of views, it has no way to filter the broadcast of change information. The view hierarchy itself is instead responsible for propagating the change information. At any level in the view hierarchy, that view knows enough about it's children to best distribute the change information further. Changes are therefore broadcasted starting from the root of the view hierarchy. The methods for doing this are:

• insertUpdate
• removeUpdate
• changedUpdate

Field Summary

static int	BadBreakWeight The weight to indicate a view is a bad break opportunity for the purpose of formatting.
static int	ExcellentBreakWeight The weight to indicate a view supports breaking, and this represents a very attractive place to break.
static int	ForcedBreakWeight The weight to indicate a view supports breaking, and must be broken to be represented properly when placed in a view that formats it's children by breaking them.
static int	GoodBreakWeight The weight to indicate a view supports breaking, but better opportunities probably exist.
static int	X_AXIS Axis for format/break operations.
static int	Y_AXIS Axis for format/break operations.

Fields inherited from interface javax.swing.SwingConstants

BOTTOM, CENTER, EAST, HORIZONTAL, LEADING, LEFT, NORTH, NORTH_EAST, NORTH_WEST, RIGHT, SOUTH, SOUTH_EAST, SOUTH_WEST, TOP, TRAILING, VERTICAL, WEST

Constructor Summary

View(Element elem)
Creates a new View object.

Method Summary

View	breakView(int axis, int offset, float pos, float len) Tries to break this view on the given axis.
void	changedUpdate(DocumentEvent e, Shape a, ViewFactory f) Gives notification from the document that attributes were changed in a location that this view is responsible for.
View	createFragment(int p0, int p1) Create a view that represents a portion of the element.
float	getAlignment(int axis) Determines the desired alignment for this view along an axis.
AttributeSet	getAttributes() Fetches the attributes to use when rendering.
int	getBreakWeight(int axis, float pos, float len) Determines how attractive a break opportunity in this view is.
Shape	getChildAllocation(int index, Shape a) Fetches the allocation for the given child view.
Container	getContainer() Fetches the container hosting the view.
Document	getDocument() Fetches the model associated with the view.
Element	getElement() Fetches the structural portion of the subject that this view is mapped to.
int	getEndOffset() Fetches the portion of the model that this view is responsible for.
float	getMaximumSpan(int axis) Determines the maximum span for this view along an axis.
float	getMinimumSpan(int axis) Determines the minimum span for this view along an axis.
int	getNextVisualPositionFrom(int pos, Position.Bias b, Shape a, int direction, Position.Bias[] biasRet) Provides a way to determine the next visually represented model location that one might place a caret.
View	getParent() Returns the parent of the view.
abstract float	getPreferredSpan(int axis) Determines the preferred span for this view along an axis.
int	getResizeWeight(int axis) Determines the resizability of the view along the given axis.
int	getStartOffset() Fetches the portion of the model that this view is responsible for.
View	getView(int n) Gets the nth child view.
int	getViewCount() Returns the number of views in this view.
ViewFactory	getViewFactory() Fetches the ViewFactory implementation that is feeding the view hierarchy.
void	insertUpdate(DocumentEvent e, Shape a, ViewFactory f) Gives notification that something was inserted into the document in a location that this view is responsible for.
boolean	isVisible() Returns a boolean that indicates whether the view is visible or not.
Shape	modelToView(int p0, Position.Bias b0, int p1, Position.Bias b1, Shape a) Provides a mapping from the document model coordinate space to the coordinate space of the view mapped to it.
Shape	modelToView(int pos, Shape a) Deprecated.
abstract Shape	modelToView(int pos, Shape a, Position.Bias b) Provides a mapping from the document model coordinate space to the coordinate space of the view mapped to it.
abstract void	paint(Graphics g, Shape allocation) Renders using the given rendering surface and area on that surface.
void	preferenceChanged(View child, boolean width, boolean height) Child views can call this on the parent to indicate that the preference has changed and should be reconsidered for layout.
void	removeUpdate(DocumentEvent e, Shape a, ViewFactory f) Gives notification from the document that attributes were removed in a location that this view is responsible for.
void	setParent(View parent) Establishes the parent view for this view.
void	setSize(float width, float height) Sets the size of the view.
int	viewToModel(float x, float y, Shape a) Deprecated.
abstract int	viewToModel(float x, float y, Shape a, Position.Bias[] biasReturn) Provides a mapping from the view coordinate space to the logical coordinate space of the model.

Methods inherited from class java.lang.Object

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

Field Detail

BadBreakWeight

public static final int BadBreakWeight

The weight to indicate a view is a bad break opportunity for the purpose of formatting. This value indicates that no attempt should be made to break the view into fragments as the view has not been written to support fragmenting.

See Also:

getBreakWeight(int, float, float), GoodBreakWeight, ExcellentBreakWeight, ForcedBreakWeight

GoodBreakWeight

public static final int GoodBreakWeight

The weight to indicate a view supports breaking, but better opportunities probably exist.

See Also:

getBreakWeight(int, float, float), BadBreakWeight, GoodBreakWeight, ExcellentBreakWeight, ForcedBreakWeight

ExcellentBreakWeight

public static final int ExcellentBreakWeight

The weight to indicate a view supports breaking, and this represents a very attractive place to break.

See Also:

getBreakWeight(int, float, float), BadBreakWeight, GoodBreakWeight, ExcellentBreakWeight, ForcedBreakWeight

ForcedBreakWeight

public static final int ForcedBreakWeight

The weight to indicate a view supports breaking, and must be broken to be represented properly when placed in a view that formats it's children by breaking them.

See Also:

getBreakWeight(int, float, float), BadBreakWeight, GoodBreakWeight, ExcellentBreakWeight, ForcedBreakWeight

X_AXIS

public static final int X_AXIS

Axis for format/break operations.

Y_AXIS

public static final int Y_AXIS

Axis for format/break operations.

Constructor Detail

View

public View(Element elem)

Creates a new View object.

Parameters:

elem - the element to represent

Method Detail

getParent

public View getParent()

Returns the parent of the view.

Returns:

the parent, null if none

isVisible

public boolean isVisible()

Returns a boolean that indicates whether the view is visible or not. By default all views are visible.

Returns:

boolean value.

getPreferredSpan

public abstract float getPreferredSpan(int axis)

Determines the preferred span for this view along an axis.

Parameters:

axis - may be either View.X_AXIS or View.Y_AXIS

See Also:

getPreferredSpan(int)

getMinimumSpan

public float getMinimumSpan(int axis)

Determines the minimum span for this view along an axis.

Parameters:

axis - may be either View.X_AXIS or View.Y_AXIS

See Also:

getPreferredSpan(int)

getMaximumSpan

public float getMaximumSpan(int axis)

Determines the maximum span for this view along an axis.

Parameters:

axis - may be either View.X_AXIS or View.Y_AXIS

See Also:

getPreferredSpan(int)

preferenceChanged

public void preferenceChanged(View child,
                              boolean width,
                              boolean height)

Child views can call this on the parent to indicate that the preference has changed and should be reconsidered for layout. By default this just propagates upward to the next parent. The root view will call revalidate on the associated text component.

Parameters:

child - the child view

width - true if the width preference has changed

height - true if the height preference has changed

See Also:

JComponent.revalidate()

getAlignment

public float getAlignment(int axis)

Determines the desired alignment for this view along an axis. By default this is simply centered.

Parameters:

axis - may be either View.X_AXIS or View.Y_AXIS

paint

public abstract void paint(Graphics g,
                           Shape allocation)

Renders using the given rendering surface and area on that surface. The view may need to do layout and create child views to enable itself to render into the given allocation.

Parameters:

g - the rendering surface to use

allocation - the allocated region to render into

See Also:

paint(java.awt.Graphics, java.awt.Shape)

setParent

public void setParent(View parent)

Establishes the parent view for this view. This is guaranteed to be called before any other methods if the parent view is functioning properly. This is also the last method called, since it is called to indicate the view has been removed from the hierarchy as well. If this is reimplemented, super.setParent() should be called.

Parameters:

parent - the new parent, or null if the view is being removed from a parent it was previously added to

getViewCount

public int getViewCount()

Returns the number of views in this view. Since the default is to not be a composite view this returns 0.

Returns:

the number of views >= 0

See Also:

getViewCount()

getView

public View getView(int n)

Gets the nth child view. Since there are no children by default, this returns null.

Parameters:

n - the number of the view to get, >= 0 && < getViewCount()

Returns:

the view

getChildAllocation

public Shape getChildAllocation(int index,
                                Shape a)

Fetches the allocation for the given child view. This enables finding out where various views are located, without assuming the views store their location. This returns null since the default is to not have any child views.

Parameters:

index - the index of the child, >= 0 && < getViewCount()

a - the allocation to this view.

Returns:

the allocation to the child

getNextVisualPositionFrom

public int getNextVisualPositionFrom(int pos,
                                     Position.Bias b,
                                     Shape a,
                                     int direction,
                                     Position.Bias[] biasRet)
                              throws BadLocationException

Provides a way to determine the next visually represented model location that one might place a caret. Some views may not be visible, they might not be in the same order found in the model, or they just might not allow access to some of the locations in the model.

Parameters:

pos - the position to convert >= 0

a - the allocated region to render into

direction - the direction from the current position that can be thought of as the arrow keys typically found on a keyboard. This may be SwingConstants.WEST, SwingConstants.EAST, SwingConstants.NORTH, or SwingConstants.SOUTH.

Returns:

the location within the model that best represents the next location visual position.

Throws:

BadLocationException -

IllegalArgumentException - for an invalid direction

modelToView

public abstract Shape modelToView(int pos,
                                  Shape a,
                                  Position.Bias b)
                           throws BadLocationException

Provides a mapping from the document model coordinate space to the coordinate space of the view mapped to it.

Parameters:

pos - the position to convert >= 0

a - the allocated region to render into

b - the bias toward the previous character or the next character represented by the offset, in case the position is a boundary of two views.

Returns:

the bounding box of the given position is returned

Throws:

BadLocationException - if the given position does not represent a valid location in the associated document

IllegalArgumentException - for an invalid bias argument

See Also:

viewToModel(float, float, java.awt.Shape, javax.swing.text.Position.Bias[])

modelToView

public Shape modelToView(int p0,
                         Position.Bias b0,
                         int p1,
                         Position.Bias b1,
                         Shape a)
                  throws BadLocationException

Provides a mapping from the document model coordinate space to the coordinate space of the view mapped to it.

Parameters:

p0 - the position to convert >= 0

b0 - the bias toward the previous character or the next character represented by p0, in case the position is a boundary of two views.

p1 - the position to convert >= 0

b1 - the bias toward the previous character or the next character represented by p1, in case the position is a boundary of two views.

a - the allocated region to render into

Returns:

the bounding box of the given position is returned

Throws:

BadLocationException - if the given position does not represent a valid location in the associated document

IllegalArgumentException - for an invalid bias argument

See Also:

viewToModel(float, float, java.awt.Shape, javax.swing.text.Position.Bias[])

viewToModel

public abstract int viewToModel(float x,
                                float y,
                                Shape a,
                                Position.Bias[] biasReturn)

Provides a mapping from the view coordinate space to the logical coordinate space of the model. The biasReturn argument will be filled in to indicate that the point given is closer to the next character in the model or the previous character in the model.

Parameters:

x - the X coordinate >= 0

y - the Y coordinate >= 0

a - the allocated region to render into

Returns:

the location within the model that best represents the given point in the view >= 0. The biasReturn argument will be filled in to indicate that the point given is closer to the next character in the model or the previous character in the model.

insertUpdate

public void insertUpdate(DocumentEvent e,
                         Shape a,
                         ViewFactory f)

Gives notification that something was inserted into the document in a location that this view is responsible for.

Parameters:

e - the change information from the associated document

a - the current allocation of the view

f - the factory to use to rebuild if the view has children

See Also:

insertUpdate(javax.swing.event.DocumentEvent, java.awt.Shape, javax.swing.text.ViewFactory)

removeUpdate

public void removeUpdate(DocumentEvent e,
                         Shape a,
                         ViewFactory f)

Gives notification from the document that attributes were removed in a location that this view is responsible for.

Parameters:

e - the change information from the associated document

a - the current allocation of the view

f - the factory to use to rebuild if the view has children

See Also:

removeUpdate(javax.swing.event.DocumentEvent, java.awt.Shape, javax.swing.text.ViewFactory)

changedUpdate

public void changedUpdate(DocumentEvent e,
                          Shape a,
                          ViewFactory f)

Gives notification from the document that attributes were changed in a location that this view is responsible for.

Parameters:

e - the change information from the associated document

a - the current allocation of the view

f - the factory to use to rebuild if the view has children

See Also:

changedUpdate(javax.swing.event.DocumentEvent, java.awt.Shape, javax.swing.text.ViewFactory)

getDocument

public Document getDocument()

Fetches the model associated with the view.

Returns:

the view model, null if none

See Also:

getDocument()

getStartOffset

public int getStartOffset()

Fetches the portion of the model that this view is responsible for.

Returns:

the starting offset into the model >= 0

See Also:

getStartOffset()

getEndOffset

public int getEndOffset()

Fetches the portion of the model that this view is responsible for.

Returns:

the ending offset into the model >= 0

See Also:

getEndOffset()

getElement

public Element getElement()

Fetches the structural portion of the subject that this view is mapped to. The view may not be responsible for the entire portion of the element.

Returns:

the subject

See Also:

getElement()

getAttributes

public AttributeSet getAttributes()

Fetches the attributes to use when rendering. By default this simply returns the attributes of the associated element. This method should be used rather than using the element directly to obtain access to the attributes to allow view-specific attributes to be mixed in or to allow the view to have view-specific conversion of attributes by subclasses. Each view should document what attributes it recognizes for the purpose of rendering or layout, and should always access them through the AttributeSet returned by this method.

breakView

public View breakView(int axis,
                      int offset,
                      float pos,
                      float len)

Tries to break this view on the given axis. This is called by views that try to do formatting of their children. For example, a view of a paragraph will typically try to place its children into row and views representing chunks of text can sometimes be broken down into smaller pieces.

This is implemented to return the view itself, which represents the default behavior on not being breakable. If the view does support breaking, the starting offset of the view returned should be the given offset, and the end offset should be less than or equal to the end offset of the view being broken.

Parameters:

axis - may be either View.X_AXIS or View.Y_AXIS

offset - the location in the document model that a broken fragment would occupy >= 0. This would be the starting offset of the fragment returned.

pos - the position along the axis that the broken view would occupy >= 0. This may be useful for things like tab calculations.

len - specifies the distance along the axis where a potential break is desired >= 0.

Returns:

the fragment of the view that represents the given span, if the view can be broken. If the view doesn't support breaking behavior, the view itself is returned.

See Also:

ParagraphView

createFragment

public View createFragment(int p0,
                           int p1)

Create a view that represents a portion of the element. This is potentially useful during formatting operations for taking measurements of fragments of the view. If the view doesn't support fragmenting (the default), it should return itself.

Parameters:

p0 - the starting offset >= 0. This should be a value greater or equal to the element starting offset and less than the element ending offset.

p1 - the ending offset > p0. This should be a value less than or equal to the elements end offset and greater than the elements starting offset.

See Also:

LabelView

getBreakWeight

public int getBreakWeight(int axis,
                          float pos,
                          float len)

Determines how attractive a break opportunity in this view is. This can be used for determining which view is the most attractive to call breakView on in the process of formatting. A view that represents text that has whitespace in it might be more attractive than a view that has no whitespace, for example. The higher the weight, the more attractive the break. A value equal to or lower than BadBreakWeight should not be considered for a break. A value greater than or equal to ForcedBreakWeight should be broken.

This is implemented to provide the default behavior of returning BadBreakWeight unless the length is greater than the length of the view in which case the entire view represents the fragment. Unless a view has been written to support breaking behavior, it is not attractive to try and break the view. An example of a view that does support breaking is LabelView. An example of a view that uses break weight is ParagraphView.

Parameters:

axis - may be either View.X_AXIS or View.Y_AXIS

pos - the potential location of the start of the broken view >= 0. This may be useful for calculating tab positions.

len - specifies the relative length from pos where a potential break is desired >= 0.

Returns:

the weight, which should be a value between ForcedBreakWeight and BadBreakWeight.

See Also:

LabelView, ParagraphView, BadBreakWeight, GoodBreakWeight, ExcellentBreakWeight, ForcedBreakWeight

getResizeWeight

public int getResizeWeight(int axis)

Determines the resizability of the view along the given axis. A value of 0 or less is not resizable.

Parameters:

axis - View.X_AXIS or View.Y_AXIS

Returns:

the weight

setSize

public void setSize(float width,
                    float height)

Sets the size of the view. This should cause layout of the view, if it has any layout duties. The default is to do nothing.

Parameters:

width - the width >= 0

height - the height >= 0

getContainer

public Container getContainer()

Fetches the container hosting the view. This is useful for things like scheduling a repaint, finding out the host components font, etc. The default implementation of this is to forward the query to the parent view.

Returns:

the container, null if none

getViewFactory

public ViewFactory getViewFactory()

Fetches the ViewFactory implementation that is feeding the view hierarchy. Normally the views are given this as an argument to updates from the model when they are most likely to need the factory, but this method serves to provide it at other times.

Returns:

the factory, null if none

modelToView

public Shape modelToView(int pos,
                         Shape a)
                  throws BadLocationException

Deprecated.

Provides a mapping from the document model coordinate space to the coordinate space of the view mapped to it. This is implemented to default the bias to Position.Bias.Forward which was previously implied.

Parameters:

pos - the position to convert >= 0

a - the allocated region to render into

Returns:

the bounding box of the given position is returned

Throws:

BadLocationException - if the given position does not represent a valid location in the associated document

See Also:

modelToView(int, java.awt.Shape, javax.swing.text.Position.Bias)

viewToModel

public int viewToModel(float x,
                       float y,
                       Shape a)

Deprecated.

Provides a mapping from the view coordinate space to the logical coordinate space of the model.

Parameters:

x - the X coordinate >= 0

y - the Y coordinate >= 0

a - the allocated region to render into

Returns:

the location within the model that best represents the given point in the view >= 0

See Also:

viewToModel(float, float, java.awt.Shape, javax.swing.text.Position.Bias[])