# Class AsyncBoxView.ChildLocator

java.lang.Object
javax.swing.text.AsyncBoxView.ChildLocator

Enclosing class:
  `AsyncBoxView`

public class AsyncBoxView.ChildLocator extends Object
A class to manage the effective position of the child views in a localized area while changes are being made around the localized area. The AsyncBoxView may be continuously changing, but the visible area needs to remain fairly stable until the layout thread decides to publish an update to the parent.

Since:
  1.3

- ## Field Summary

  Fields
  Modifier and Type
  Field
  Description
  `protected Rectangle`
  `childAlloc`
  A shape to use for the child allocation to avoid creating a lot of garbage.
  `protected Rectangle`
  `lastAlloc`
  The last seen allocation (for repainting when changes are flushed upward).
  `protected AsyncBoxView.ChildState`
  `lastValidOffset`
  The location of the last offset calculation that is valid.

- ## Constructor Summary

  Constructors
  Constructor
  Description
  `ChildLocator()`
  construct a child locator.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `void`
  `childChanged(AsyncBoxView.ChildState cs)`
  Notification that a child changed.
  `protected Shape`
  `getChildAllocation(int index)`
  Fetch the allocation to use for a child view.
  `Shape`
  `getChildAllocation(int index, Shape a)`
  Fetch the allocation to use for a child view.
  `int`
  `getViewIndexAtPoint(float x, float y, Shape a)`
  Fetches the child view index at the given point.
  `protected int`
  `getViewIndexAtVisualOffset(float targetOffset)`
  Locate the view responsible for an offset into the box along the major axis.
  `void`
  `paintChildren(Graphics g)`
  Paint the children that intersect the clip area.
  `protected void`
  `setAllocation(Shape a)`
  Copy the currently allocated shape into the Rectangle used to store the current allocation.

  ### Methods declared in class Object

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

- ## Field Details

  - ### lastValidOffset

    protected AsyncBoxView.ChildState lastValidOffset
    The location of the last offset calculation that is valid.

  - ### lastAlloc

    protected Rectangle lastAlloc
    The last seen allocation (for repainting when changes are flushed upward).

  - ### childAlloc

    protected Rectangle childAlloc
    A shape to use for the child allocation to avoid creating a lot of garbage.

- ## Constructor Details

  - ### ChildLocator

    public ChildLocator()
    construct a child locator.

- ## Method Details

  - ### childChanged

    public void childChanged(AsyncBoxView.ChildState cs)
    Notification that a child changed. This can effect whether or not new offset calculations are needed. This is called by a ChildState object that has changed it's major span. This can therefore be called by multiple threads.
    Parameters:
      `cs` - the child state

  - ### paintChildren

    public void paintChildren(Graphics g)
    Paint the children that intersect the clip area.
    Parameters:
      `g` - the rendering surface to use

  - ### getChildAllocation

    public Shape getChildAllocation(int index, Shape a)
    Fetch the allocation to use for a child view. This will update the offsets for all children not yet updated before the given index.
    Parameters:
      `index` - the child index
      `a` - the allocation
    Returns:
      the allocation to use for a child view

  - ### getViewIndexAtPoint

    public int getViewIndexAtPoint(float x, float y, Shape a)
    Fetches the child view index at the given point. This is called by the various View methods that need to calculate which child to forward a message to. This should be called by a block synchronized on this object, and would typically be followed with one or more calls to getChildAllocation that should also be in the synchronized block.
    Parameters:
      `x` - the X coordinate >= 0
      `y` - the Y coordinate >= 0
      `a` - the allocation to the View
    Returns:
      the nearest child index

  - ### getChildAllocation

    protected Shape getChildAllocation(int index)
    Fetch the allocation to use for a child view. This does not update the offsets in the ChildState records.
    Parameters:
      `index` - the index
    Returns:
      the allocation to use for a child view

  - ### setAllocation

    protected void setAllocation(Shape a)
    Copy the currently allocated shape into the Rectangle used to store the current allocation. This would be a floating point rectangle in a Java2D-specific implementation.
    Parameters:
      `a` - the allocation

  - ### getViewIndexAtVisualOffset

    protected int getViewIndexAtVisualOffset(float targetOffset)
    Locate the view responsible for an offset into the box along the major axis. Make sure that offsets are set on the ChildState objects up to the given target span past the desired offset.
    Parameters:
      `targetOffset` - the target offset
    Returns:
      index of the view representing the given visual location (targetOffset), or -1 if no view represents that location