javax.swing.text

Class View

Contents
  • All Implemented Interfaces:
    SwingConstants
    Direct Known Subclasses:
    AsyncBoxView, ComponentView, CompositeView, GlyphView, IconView, ImageView, 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.

    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 its 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 independently 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 above text describes this graphic.

    The minimum set of methods for layout are:

    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 view's 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:

    Sample calling sequence between parent view and child view: setSize, getMinimum, getPreferred, getMaximum, getAlignment, setSize

    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 its 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 efficient 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 its entire allocation, typically a view does not. Rendering is performed by tranversing down the tree of View implementations. Each View is responsible for rendering its 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:

    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:

    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 its 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:

    • 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, or null if none exists

      • isVisible

        public boolean isVisible()
        Returns a boolean that indicates whether the view is visible or not. By default all views are visible.
        Returns:
        always returns true

      • 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
        Returns:
        the span the view would like to be rendered into. Typically the view is told to render into the span that is returned, although there is no guarantee. The parent may choose to resize or break the view
        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
        Returns:
        the minimum span the view can be rendered into
        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
        Returns:
        the maximum span the view can be rendered into
        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. The desired alignment is returned. This should be a value >= 0.0 and <= 1.0, where 0 indicates alignment at the origin and 1.0 indicates alignment to the full span away from the origin. An alignment of 0.5 would be the center of the view.
        Parameters:
        axis - may be either View.X_AXIS or View.Y_AXIS
        Returns:
        the value 0.5

      • 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

      • 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. When this method is called to set the parent to null, this method does the same for each of its children, propogating the notification that they have been disconnected from the view tree. 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

      • 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

      • removeAll

        public void removeAll()
        Removes all of the children. This is a convenience call to replace.
        Since:
        1.3

      • remove

        public void remove(int i)
        Removes one of the children at the given position. This is a convenience call to replace.
        Since:
        1.3

      • insert

        public void insert(int offs,
          View v)
        Inserts a single child view. This is a convenience call to replace.
        Parameters:
        offs - the offset of the view to insert before >= 0
        v - the view
        Since:
        1.3
        See Also:
        replace(int, int, javax.swing.text.View[])

      • replace

        public void replace(int offset,
           int length,
           View[] views)
        Replaces child views. If there are no views to remove this acts as an insert. If there are no views to add this acts as a remove. Views being removed will have the parent set to null, and the internal reference to them removed so that they can be garbage collected. This is implemented to do nothing, because by default a view has no children.
        Parameters:
        offset - the starting index into the child views to insert the new views. This should be a value >= 0 and <= getViewCount
        length - the number of existing child views to remove This should be a value >= 0 and <= (getViewCount() - offset).
        views - the child views to add. This value can be null to indicate no children are being added (useful to remove).
        Since:
        1.3

      • getViewIndex

        public int getViewIndex(int pos,
               Position.Bias b)
        Returns the child view index representing the given position in the model. By default a view has no children so this is implemented to return -1 to indicate there is no valid child index for any position.
        Parameters:
        pos - the position >= 0
        Returns:
        index of the view representing the given position, or -1 if no view represents that position
        Since:
        1.3

      • 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 how 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 at which 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 in which to render
        direction - the direction from the current position that can be thought of as the arrow keys typically found on a keyboard. This will be one of the following values:
        • SwingConstants.WEST
        • SwingConstants.EAST
        • SwingConstants.NORTH
        • SwingConstants.SOUTH
        Returns:
        the location within the model that best represents the next location visual position
        Throws:
        BadLocationException
        IllegalArgumentException - if direction doesn't have one of the legal values above

      • modelToView

        public abstract Shape modelToView(int pos,
                Shape a,
                Position.Bias b)
                           throws BadLocationException
        Provides a mapping, for a given character, from the document model coordinate space to the view coordinate space.
        Parameters:
        pos - the position of the desired character (>=0)
        a - the area of the view, which encompasses the requested character
        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; b will have one of these values:
        • Position.Bias.Forward
        • Position.Bias.Backward
        Returns:
        the bounding box, in view coordinate space, of the character at the specified position
        Throws:
        BadLocationException - if the specified position does not represent a valid location in the associated document
        IllegalArgumentException - if b is not one of the legal Position.Bias values listed above
        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, for a given region, from the document model coordinate space to the view coordinate space. The specified region is created as a union of the first and last character positions.
        Parameters:
        p0 - the position of the first character (>=0)
        b0 - the bias of the first character position, toward the previous character or the next character represented by the offset, in case the position is a boundary of two views; b0 will have one of these values:
        • Position.Bias.Forward
        • Position.Bias.Backward
        p1 - the position of the last character (>=0)
        b1 - the bias for the second character position, defined one of the legal values shown above
        a - the area of the view, which encompasses the requested region
        Returns:
        the bounding box which is a union of the region specified by the first and last character positions
        Throws:
        BadLocationException - if the given position does not represent a valid location in the associated document
        IllegalArgumentException - if b0 or b1 are not one of the legal Position.Bias values listed above
        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 in which to render
        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. To reduce the burden to subclasses, this functionality is spread out into the following calls that subclasses can reimplement:
        1. updateChildren is called if there were any changes to the element this view is responsible for. If this view has child views that are represent the child elements, then this method should do whatever is necessary to make sure the child views correctly represent the model.
        2. forwardUpdate is called to forward the DocumentEvent to the appropriate child views.
        3. updateLayout is called to give the view a chance to either repair its layout, to reschedule layout, or do nothing.
        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 that something was removed from the document in a location that this view is responsible for. To reduce the burden to subclasses, this functionality is spread out into the following calls that subclasses can reimplement:
        1. updateChildren is called if there were any changes to the element this view is responsible for. If this view has child views that are represent the child elements, then this method should do whatever is necessary to make sure the child views correctly represent the model.
        2. forwardUpdate is called to forward the DocumentEvent to the appropriate child views.
        3. updateLayout is called to give the view a chance to either repair its layout, to reschedule layout, or do nothing.
        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. To reduce the burden to subclasses, this functionality is spread out into the following calls that subclasses can reimplement:
        1. updateChildren is called if there were any changes to the element this view is responsible for. If this view has child views that are represent the child elements, then this method should do whatever is necessary to make sure the child views correctly represent the model.
        2. forwardUpdate is called to forward the DocumentEvent to the appropriate child views.
        3. updateLayout is called to give the view a chance to either repair its layout, to reschedule layout, or do nothing.
        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 for which this view is responsible.
        Returns:
        the starting offset into the model >= 0
        See Also:
        getStartOffset()

      • getEndOffset

        public int getEndOffset()
        Fetches the portion of the model for which this view is responsible.
        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()

      • getGraphics

        public Graphics getGraphics()
        Fetch a Graphics for rendering. This can be used to determine font characteristics, and will be different for a print view than a component view.
        Returns:
        a Graphics object for rendering
        Since:
        1.3

      • 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)
        Creates 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.
        Returns:
        the view fragment, or itself if the view doesn't support breaking into fragments
        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 - may be either 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 along the given axis, if it has any layout duties.
        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

      • getViewIndex

        public int getViewIndex(float x,
               float y,
               Shape allocation)
        Returns the child view index representing the given position in the view. This iterates over all the children returning the first with a bounds that contains x, y.
        Parameters:
        x - the x coordinate
        y - the y coordinate
        allocation - current allocation of the View.
        Returns:
        index of the view representing the given location, or -1 if no view represents that position
        Since:
        1.4

      • modelToView

        @Deprecated
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 in which to render
        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

        @Deprecated
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 in which to render
        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[])

Document created the 11/06/2005, last modified the 04/03/2020
Source of the printed document:https://www.gaudry.be/en/java-api-rf-javax/swing/text/view.html

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