Bug 15844 [Exception Handling] SelectionChange events and NPE
Build 20020508 Due to new global actions there are now more objects listening to selection changes send out by a JFace viewer. We now had the case that one of the listener generated a NPE. As a result all listeners registered after that one didn't receive the selection change event. StructuredViewers should be more fault tolorant to exceptions when informing listeners.
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/CheckboxTreeViewer.java
*/
protected void preservingSelection(Runnable updateCode) {
	int n = getItemCount(getControl());
	Set checkedNodes = new HashSet(n);
	Set grayedNodes = new HashSet(n);
	gatherState(checkedNodes, grayedNodes, getControl());
	super.preservingSelection(updateCode);
	applyState(checkedNodes, grayedNodes, getControl());
}
/* (non-Javadoc)
 * Method declared on ICheckable.
 */
public void removeCheckStateListener(ICheckStateListener listener) {
	checkStateListeners.remove(listener);
}
/* (non-Javadoc)
 * Method declared on ICheckable.
 */
public boolean setChecked(Object element, boolean state) {
	Widget widget = internalExpand(element, false);
	if (widget instanceof TreeItem) {
		((TreeItem) widget).setChecked(state);
		return true;
	}
	return false;
}
/**
 * Sets the checked state for the children of the given item.
 *
 * @param item the item