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
* @see ICellEditorListener#editorValueChanged
     */
    protected void valueChanged(boolean oldValidState, boolean newValidState) {
        valid = newValidState;
        dirty = true;
        fireEditorValueChanged(oldValidState, newValidState);
    }
    
    /**
     * Activate the editor but also inform the editor which event triggered its activation.
     * <b>The default implementation simply calls {@link #activate()}</b>
     * 
     * @param activationEvent the editor activation event
     * @since 3.3
     */
    public void activate(ColumnViewerEditorActivationEvent activationEvent) {
    	activate();
    }
    
    /**
     * This method is for interal use in {@link ColumnViewerEditor} to not break clients
     * who don't implement the {@link ICellEditorListener} appropiately
     * 
     * @return <code>true</code> to indicate that a focus listener has to be attached
     */
    boolean dependsOnExternalFocusListener() {
    	return true;
    }
}