我需要一个带有附加下拉式菜单的 JButton。所以我采用了 JPopupMenu 并将其附加到 JButton，如下面的代码所示。它需要做的是:

• 点击时显示弹出窗口
• 第二次点击隐藏
• 如果在弹出窗口中选择了一个项目则隐藏它
• 如果用户点击屏幕上的其他地方则隐藏它

这 4 件事有效，但由于我使用的 boolean 标志，如果用户单击其他地方或选择一个项目，我必须在按钮再次显示之前单击两次。这就是为什么我尝试添加一个 FocusListener(它绝对没有响应)来解决这个问题并在这些情况下将标志设置为 false。

编辑:在回答帖子中的最后一次尝试......

这是监听器:(它在扩展 JButton 的类中，所以第二个监听器在 JButton 上。)

// Show popup on left click.
menu.addFocusListener(new FocusListener() {
 @Override
 public void focusLost(FocusEvent e) {
  System.out.println("LOST FOCUS");
  isShowingPopup = false;
 }

 @Override
 public void focusGained(FocusEvent e) {
  System.out.println("GAINED FOCUS");
 }
});

addActionListener(new ActionListener() {
 @Override
 public void actionPerformed(ActionEvent e) {
  System.out.println("isShowingPopup: " + isShowingPopup);
  if (isShowingPopup) {
   isShowingPopup = false;
  } else {
   Component c = (Component) e.getSource();
   menu.show(c, -1, c.getHeight());
   isShowingPopup = true;
  }
 }
});

我已经为此纠结太久了。如果有人能告诉我这有什么问题，那就太好了!

谢谢!

代码:

public class Button extends JButton {

    // Icon.
    private static final ImageIcon ARROW_SOUTH = new ImageIcon("ArrowSouth.png");

    // Unit popup menu.
    private final JPopupMenu menu;

    // Is the popup showing or not?
    private boolean isShowingPopup = false;

    public Button(int height) {
        super(ARROW_SOUTH);
        menu = new JPopupMenu(); // menu is populated somewhere else

        // FocusListener on the JPopupMenu
        menu.addFocusListener(new FocusListener() {
            @Override
            public void focusLost(FocusEvent e) {
                System.out.println("LOST FOCUS");
                isShowingPopup = false;
            }

            @Override
            public void focusGained(FocusEvent e) {
                System.out.println("GAINED FOCUS");
            }
        });

        // ComponentListener on the JPopupMenu
        menu.addComponentListener(new ComponentListener() {
            @Override
            public void componentShown(ComponentEvent e) {
                System.out.println("SHOWN");
            }

            @Override
            public void componentResized(ComponentEvent e) {
                System.out.println("RESIZED");
            }

            @Override
            public void componentMoved(ComponentEvent e) {
                System.out.println("MOVED");
            }

            @Override
            public void componentHidden(ComponentEvent e) {
                System.out.println("HIDDEN");
            }
        });

        // ActionListener on the JButton
        addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                System.out.println("isShowingPopup: " + isShowingPopup);
                if (isShowingPopup) {
                    menu.requestFocus();
                    isShowingPopup = false;
                } else {
                    Component c = (Component) e.getSource();
                    menu.show(c, -1, c.getHeight());
                    isShowingPopup = true;
                }
            }
        });

        // Skip when navigating with TAB.
        setFocusable(true); // Was false first and should be false in the end.

        menu.setFocusable(true);
    }

}

最佳答案

这是我刚刚提出的 Amber Shah 的“大黑客”建议的变体。没有 isShowingPopup 标志...

它不是防弹的，但它工作得很好，直到有人以非常慢的速度点击关闭弹出窗口(或非常快速的第二次点击以重新打开它......)。

public class Button extends JButton {

 // Icon.
 private static final ImageIcon ARROW_SOUTH = new ImageIcon("ArrowSouth.png");

 // Popup menu.
 private final JPopupMenu menu;

 // Last time the popup closed.
 private long timeLastShown = 0;

 public Button(int height) {
  super(ARROW_SOUTH);
  menu = new JPopupMenu(); // Populated somewhere else.

  // Show and hide popup on left click.
  menu.addPopupMenuListener(new PopupMenuListener() {
   @Override
   public void popupMenuWillBecomeInvisible(PopupMenuEvent arg0) {
    timeLastShown = System.currentTimeMillis();
   }
   @Override public void popupMenuWillBecomeVisible(PopupMenuEvent arg0) {}
   @Override public void popupMenuCanceled(PopupMenuEvent arg0) {}
  });
  addActionListener(new ActionListener() {
   @Override
   public void actionPerformed(ActionEvent e) {
    if ((System.currentTimeMillis() - timeLastShown) > 300) {
     Component c = (Component) e.getSource();
     menu.show(c, -1, c.getHeight());
    }
   }
  });

  // Skip when navigating with TAB.
  setFocusable(false);
 }

}

正如我在评论中所说，这不是最优雅的解决方案，但它非常简单并且在 98% 的情况下都有效。

愿意接受建议!

关于java - 从 JButton 显示/隐藏 JPopupMenu； FocusListener 不工作？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/2421914/