public ChildState(View v) 
{
            child = v;
            minorValid = false;
            majorValid = false;
            childSizeValid = false;
            child.setParent(AsyncBoxView.this);
}

Construct a child status. This needs to start out as fairly large so we don't falsely begin with the idea that all of the children are visible.

since: 1.4 -

 public View getChildView() 
{
            return child;
}

Fetch the child view this record represents

 public float getMajorOffset() 
{
            return offset;
}

Get the offset along the major axis

 public float getMajorSpan() 
{
            return span;
}

What is the span along the major axis.

 public float getMinorOffset() 
{
            if (max <  minorSpan) {
                // can't make the child this wide, align it
                float align = child.getAlignment(getMinorAxis());
                return ((minorSpan - max) * align);
            }
            return 0f;
}

What is the offset along the minor axis

 public float getMinorSpan() 
{
            if (max <  minorSpan) {
                return max;
            }
            // make it the target width, or as small as it can get.
            return Math.max(min, minorSpan);
}

What is the span along the minor axis.

 public boolean isLayoutValid() 
{
            return (minorValid && majorValid && childSizeValid);
}

Has the child view been laid out.

 public  void preferenceChanged(boolean width,
    boolean height) 
{
            if (axis == X_AXIS) {
                if (width) {
                    majorValid = false;
                }
                if (height) {
                    minorValid = false;
                }
            } else {
                if (width) {
                    minorValid = false;
                }
                if (height) {
                    majorValid = false;
                }
            }
            childSizeValid = false;
}

Mark preferences changed for this child.

 public  void run() 
{
            AbstractDocument doc = (AbstractDocument) getDocument();
            try {
                doc.readLock();
                if (minorValid && majorValid && childSizeValid) {
                    // nothing to do
                    return;
                }
                if (child.getParent() == AsyncBoxView.this) {
                    // this may overwrite anothers threads cached
                    // value for actively changing... but that just
                    // means it won't use the cache if there is an
                    // overwrite.
                    synchronized(AsyncBoxView.this) {
                        changing = this;
                    }
                    updateChild();
                    synchronized(AsyncBoxView.this) {
                        changing = null;
                    }
                    // setting the child size on the minor axis
                    // may have caused it to change it's preference
                    // along the major axis.
                    updateChild();
                }
            } finally {
                doc.readUnlock();
            }
}

Update the child state. This should be called by the thread that desires to spend time updating the child state (intended to be the layout thread).

This aquires a read lock on the associated document for the duration of the update to ensure the model is not changed while it is operating. The first thing to do would be to see if any work actually needs to be done. The following could have conceivably happened while the state was waiting to be updated:

1. The child may have been removed from the view hierarchy.
2. The child may have been updated by a higher priority operation (i.e. the child may have become visible).

 public  void setMajorOffset(float offs) 
{
            offset = offs;
}

This method should only be called by the ChildLocator, it is simply a convenient place to hold the cached location.

  void updateChild() 
{
            boolean minorUpdated = false;
            synchronized(this) {
                if (! minorValid) {
                    int minorAxis = getMinorAxis();
                    min = child.getMinimumSpan(minorAxis);
                    pref = child.getPreferredSpan(minorAxis);
                    max = child.getMaximumSpan(minorAxis);
                    minorValid = true;
                    minorUpdated = true;
                }
            }
            if (minorUpdated) {
                minorRequirementChange(this);
            }
            boolean majorUpdated = false;
            float delta = 0.0f;
            synchronized(this) {
                if (! majorValid) {
                    float old = span;
                    span = child.getPreferredSpan(axis);
                    delta = span - old;
                    majorValid = true;
                    majorUpdated = true;
                }
            }
            if (majorUpdated) {
                majorRequirementChange(this, delta);
                locator.childChanged(this);
            }
            synchronized(this) {
                if (! childSizeValid) {
                    float w;
                    float h;
                    if (axis == X_AXIS) {
                        w = span;
                        h = getMinorSpan();
                    } else {
                        w = getMinorSpan();
                        h = span;
                    }
                    childSizeValid = true;
                    child.setSize(w, h);
                }
            }
}