Bug 58777 [Viewers] add API to not deactivate CellEditor on FocusLost
TableViewerImpl installs a FocusListener on CellEditors, which calls applyEditorValue() on focusLost events. This FocusListener must be removed since applying the editor value is not always the wanted behavior on focusLost. Subclasses of CellEditor already handle focus loss in an extensible way: they install their own FocusListener and call a hook method focusLost() (which can be extended or reimplemented by subclasses with special needs). To support content assist in table cells (such as in the Change Method Signature dialog), we need to stay in editing mode even while the proposal list has focus. This is currently not implementable, since TableViewerImpl deactivates the CellEditor even if the CellEditor's focusLost() is reimplemented. The fix is to simply remove the redundant FocusListener in TableViewerImpl.
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/CellEditor.java
true).x;
        }
        return result;
    }
    /**
     * Returns the input validator for this cell editor.
     *
     * @return the input validator, or <code>null</code> if none
     */
    public ICellEditorValidator getValidator() {
        return validator;
    }
    /**
     * Returns this cell editor's value provided that it has a valid one.
     *
     * @return the value of this cell editor, or <code>null</code>
     *   if the cell editor does not contain a valid value
     */
    public final Object getValue() {
        if (!valid) {
			return null;
		}
        return doGetValue();
    }
    /**
     * Returns whether this cell editor is activated.
     *
     * @return <code>true</code> if this cell editor's control is
     *   currently activated, and <code>false</code> if not activated
     */