JPanel 哪个监听器适合可见性已更改

2022-09-01 22:51:53

是否有一些规则,或与 的好/坏体验,或监听和的变化的可见性?AncestorListenerComponentListenerHierarchyListenerJPanelJComponents

其中一个是否比其他更好或更安全?我特别想知道何时以及如何隐藏/被隐藏。JPanelJComponent

请注意,以下代码包含不正确的 Swing 规则,例如在本例中使用 ,以允许我在 Swing GUI 中打印出正确的顺序Thread.sleep(int)Listeners

import java.awt.BorderLayout;
import java.awt.CardLayout;
import java.awt.event.ComponentEvent;
import java.awt.event.ComponentListener;
import java.awt.event.HierarchyEvent;
import java.awt.event.HierarchyListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.event.AncestorEvent;
import javax.swing.event.AncestorListener;

public class CardlayoutTest extends JFrame {

    private static final long serialVersionUID = 1L;
    public CardLayout card = new CardLayout();

    public CardlayoutTest() {
        JPanel pnlA = new JPanel(new BorderLayout());
        pnlA.add(new JButton("A"), BorderLayout.CENTER);
        JPanel pnlB = new JPanel(new BorderLayout());
        pnlB.add(new JButton("B"), BorderLayout.CENTER);
        JPanel pnlC = new JPanel(new BorderLayout());
        pnlC.add(new JButton("C"), BorderLayout.CENTER);

        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setLayout(card);
        add(pnlA, "A");
        add(pnlB, "B");
        add(pnlC, "C");

        pnlA.addAncestorListener(new EventHandler());
        pnlB.addAncestorListener(new EventHandler());
        pnlC.addAncestorListener(new EventHandler());

        pnlA.addHierarchyListener(new EventHandler());
        pnlB.addHierarchyListener(new EventHandler());
        pnlB.addHierarchyListener(new EventHandler());

        pnlA.addComponentListener(new EventHandler());
        pnlB.addComponentListener(new EventHandler());
        pnlB.addComponentListener(new EventHandler());
    }

    class EventHandler implements AncestorListener, ComponentListener, HierarchyListener {

        @Override
        public void ancestorAdded(AncestorEvent event) {
            System.out.println("CardlayoutTest.EventHandler.ancestorAdded()");
        }

        @Override
        public void ancestorMoved(AncestorEvent event) {
            System.out.println("CardlayoutTest.EventHandler.ancestorMoved()");
        }

        @Override
        public void ancestorRemoved(AncestorEvent event) {
            System.out.println("CardlayoutTest.EventHandler.ancestorRemoved()");
        }

        @Override
        public void hierarchyChanged(HierarchyEvent e) {
            System.out.println("Components Change: " + e.getChanged());
            if ((e.getChangeFlags() & HierarchyEvent.DISPLAYABILITY_CHANGED) != 0) {
                if (e.getComponent().isDisplayable()) {
                    System.out.println("Components DISPLAYABILITY_CHANGED : " + e.getChanged());
                } else {
                    System.out.println("Components DISPLAYABILITY_CHANGED : " + e.getChanged());
                }
            }
            if ((e.getChangeFlags() & HierarchyEvent.SHOWING_CHANGED) != 0) {
                if (e.getComponent().isDisplayable()) {
                    System.out.println("Components SHOWING_CHANGED : " + e.getChanged());
                } else {
                    System.out.println("Components SHOWING_CHANGED : " + e.getChanged());
                }
            }
        }

        public void componentHidden(ComponentEvent e) {
            System.out.println(e.getComponent().getClass().getName() + " --- Hidden");
        }

        public void componentMoved(ComponentEvent e) {
            System.out.println(e.getComponent().getClass().getName() + " --- Moved");
        }

        public void componentResized(ComponentEvent e) {
            System.out.println(e.getComponent().getClass().getName() + " --- Resized ");
        }

        public void componentShown(ComponentEvent e) {
            System.out.println(e.getComponent().getClass().getName() + " --- Shown");
        }
    }

    public static void main(String[] args) {
        CardlayoutTest t = new CardlayoutTest();
        t.setSize(500, 500);
        System.out.println("CardlayoutTest.main()------------------------ FIRST");
        t.card.show(t.getContentPane(), "A");
        t.setVisible(true);
        System.out.print("\n");
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
        }
        System.out.println("CardlayoutTest.main()------------------------ SECOND");
        t.card.show(t.getContentPane(), "B");
        System.out.print("\n");
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
        }
        System.out.println("CardlayoutTest.main()------------------------ THIRD");
        t.card.show(t.getContentPane(), "C");
        System.out.print("\n");
    }
}

答案 1

如果您想准确地收听可见性变化 - 请使用或:ComponentListenerComponentAdapter

    JPanel panel = new JPanel ();
    panel.addComponentListener ( new ComponentAdapter ()
    {
        public void componentShown ( ComponentEvent e )
        {
            System.out.println ( "Component shown" );
        }

        public void componentHidden ( ComponentEvent e )
        {
            System.out.println ( "Component hidden" );
        }
    } );

但这种可见性可能不是你想到的。 标志将是,即使 没有添加到任何,因此根本不显示!isVisible()trueComponentContainer

这种可见性a具有略微不同的目的。您可以使用它来手动隐藏已添加并显示在应用程序中某个位置的。在这种情况下,(如果您使用)它将被隐藏,并且将通知每一项更改。ComponentsetVisible(false)ComponentListenerComponent

所以,谈论实际的可见性...

这是您应该用来监听实际组件外观/消失的内容:

    JPanel panel = new JPanel ();
    panel.addAncestorListener ( new AncestorListener ()
    {
        public void ancestorAdded ( AncestorEvent event )
        {
            // Component added somewhere
        }

        public void ancestorRemoved ( AncestorEvent event )
        {
            // Component removed from container
        }

        public void ancestorMoved ( AncestorEvent event )
        {
            // Component container moved
        }
    } );

我总是使用该侦听器来确定何时在某处添加,并在移动/删除时侦听。Component

此外,您可以随时通过调用方法检查应用程序用户是否实际可见:ComponentisShowing()

boolean userCanSeeThePanel = panel.isShowing();

仅当该面板已添加到 VISIBLE 到用户框架并且标志也为真时,才会返回(通常为 ,除非您将其设置为 )。trueisVisible()truefalse

我想这就是我能告诉你的关于可见性的全部内容。我可能误解了你的问题。如果我在这种情况下错了,请纠正我。


答案 2

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