Question

AncestorListener，ComponentListener或HierarchyListener是否有关于JPanel和JComponents的变更可见情况的规则或好/坏体验？< / p>

其中一个比其他人更好还是更安全？我特别想知道隐藏JPanel / JComponent的时间和方式。

请注意，以下代码包含不正确的Swing规则，例如在这种情况下使用Thread.sleep(int)，以允许我在Swing GUI中打印出Listeners的正确顺序

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");
    }
}

Answer 1

如果您想完全听取可见性更改，请使用ComponentListener或ComponentAdapter：

    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" );
        }
    } );

但是，这种可见度可能不是你想到的。即使isVisible()没有添加到任何true，因此Component标记也会Container，因此根本不显示！

该可见性a的目的略有不同。您可以使用它来手动隐藏已添加并显示在应用程序中某处的Component。在这种情况下，（如果您使用setVisible(false)）它将被隐藏，并且ComponentListener的每个Component都会被告知该更改。

所以，谈论实际可见性......

这是您应该用来聆听实际组件出现/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Component，以及在移动/移除时监听。

此外，您始终可以通过调用Component方法检查应用程序用户是否确实可以看到isShowing()：

boolean userCanSeeThePanel = panel.isShowing();

仅当该面板被添加到VISIBLE到用户框架且true标志也为真时（通常为isVisible()），这将返回true，除非您将其设置为{{1} }}）。

我想我可以告诉你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。

听众的哪一个适合可见性的JPanel被改变了

1 个答案: