DocumentViewOp.java 文件源码

private void updateListeners() {
    ScrollPaneUI ui = scrollPane.getUI();
    if (ui != lastUI) {
        // Update "ui" property listener
        if (ui != null) {
            // Check mouse wheel listeners on scroll pane.
            // Pair first non-MWDelegator listener with 
            // Remove any other delegators than this one.
            MouseWheelListener[] mwls = scrollPane.getListeners(MouseWheelListener.class);
            if (LOG.isLoggable(Level.FINE)) {
                LOG.log(Level.FINE, "MouseWheelDelegator.updateListeners(): scrollPane change scrollPane={0}, MouseWheelListeners:{1}\n",
                        new Object[]{obj2String(scrollPane), Arrays.asList(mwls)});
            }
            delegateListener = null;
            for (MouseWheelListener listener : mwls) {
                if (listener instanceof MouseWheelDelegator) {
                    scrollPane.removeMouseWheelListener(listener);
                    if (delegateListener == null) {
                        delegateListener = ((MouseWheelDelegator) listener).delegateListener;
                        scrollPane.addMouseWheelListener(this);
                    }
                } else { // Regular listener 
                    // Current patch only assumes one MW listener attached by the UI impl.
                    if (delegateListener == null) {
                        delegateListener = listener;
                        scrollPane.removeMouseWheelListener(listener);
                        scrollPane.addMouseWheelListener(this);
                    }
                }
            }
        }
        lastUI = ui;
    }
}