Java Swing中的JButton悬停动画

Question

我工作在图形用户界面窗口与Swing，我想创建一个导航菜单。当鼠标悬停在导航菜单的按钮上时，我想给它们添加一个动画。

像这样的东西：

​

​

我不能使用鼠标侦听器，因为它只是在没有动画的情况下在颜色之间切换，就像这样

​

​

翻滚需要gif，不同的屏幕大小需要不同的gif大小。

有没有办法做到这一点呢?如何抛出代码？

Answer 1

这是一个比MadProgrammer建议的简单得多的实现。它做了一些天真的假设，比如线性颜色插值。它也不会尝试动画颜色的alpha混合。而且它不支持响应键盘导航的动画。

内部Fader类使用javax.swing.Timer在一个方向上制作动画。为每个JMenuItem指定两个渐变对象，一个用于过渡到高光颜色，另一个用于过渡回常规背景颜色。

还有必要重写UI委托对象，因为大多数外观都希望强制使用自己的颜色，而不管JMenuItem的背景是什么，无论是在菜单项始终具有键盘焦点时都是如此。

import java.util.Objects;

import java.awt.Color;
import java.awt.Component;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;

import javax.swing.AbstractButton;
import javax.swing.BorderFactory;
import javax.swing.JLabel;
import javax.swing.JFrame;
import javax.swing.JMenuItem;
import javax.swing.JPopupMenu;
import javax.swing.Timer;
import javax.swing.plaf.basic.BasicMenuItemUI;

public class FadingMenuTest {
    private static final int animDurationMillis = 500;
    private static final int frameCount = 8;

    private static class Fader {
        private final Component component;

        private final Color normalBackground;
        private final float[] normalRGBA;
        private final float[] targetRGBA;
        private final float[] rgba = new float[4];

        private final Timer timer = new Timer(animDurationMillis / frameCount,
            e -> updateBackground());

        private int frameNumber;

        Fader(Component component,
              Color targetBackground,
              Color normalBackground) {

            this.component = Objects.requireNonNull(component);
            this.normalBackground = normalBackground;
            this.normalRGBA = normalBackground.getComponents(null);
            this.targetRGBA = targetBackground.getComponents(null);
        }

        private void updateBackground() {
            if (++frameNumber > frameCount) {
                timer.stop();
                return;
            }

            for (int i = rgba.length - 1; i >= 0; i--) {
                float normal = normalRGBA[i];
                float target = targetRGBA[i];
                rgba[i] =
                    normal + (target - normal) * frameNumber / frameCount;
            }

            component.setBackground(
                new Color(rgba[0], rgba[1], rgba[2], rgba[3]));
        }

        void start() {
            frameNumber = 0;
            timer.restart();
            component.setBackground(normalBackground);
        }

        void stop() {
            timer.stop();
            component.setBackground(normalBackground);
        }
    }

    static void addFadeOnHover(Component component,
                               Color targetBackground,
                               Color normalBackground) {

        Fader entryFader =
            new Fader(component, targetBackground, normalBackground);
        Fader exitFader =
            new Fader(component, normalBackground, targetBackground);

        component.addMouseListener(new MouseAdapter() {
            private static final long serialVersionUID = 1;

            @Override
            public void mouseEntered(MouseEvent event) {
                exitFader.stop();
                entryFader.start();
            }

            @Override
            public void mouseExited(MouseEvent event) {
                entryFader.stop();
                exitFader.start();
            }
        });
    }

    static void show() {
        Color foreground = Color.WHITE;
        Color background = new Color(0, 0, 128);
        Color highlight = Color.BLUE;

        JPopupMenu menu = new JPopupMenu();
        menu.setBackground(background);

        menu.add(new JMenuItem(String.format("%c Backup", 0x1f5ce)));
        menu.add(new JMenuItem(String.format("%c Screenshots", 0x1f5b5)));
        menu.add(new JMenuItem("\u26ed Settings"));

        // Most look-and-feels will override any colors we set, especially
        // when a menu item is selected.
        BasicMenuItemUI ui = new BasicMenuItemUI() {
            {
                selectionForeground = foreground;
                selectionBackground = background;
            }

            @Override
            public void paintBackground(Graphics g,
                                        JMenuItem item,
                                        Color background) {
                super.paintBackground(g, item, item.getBackground());
            }
        };

        for (Component item : menu.getComponents()) {
            AbstractButton b = (AbstractButton) item;
            b.setContentAreaFilled(false);
            b.setOpaque(true);
            b.setUI(ui);

            item.setForeground(foreground);
            item.setBackground(background);
            addFadeOnHover(item, highlight, background);
        }

        JLabel label = new JLabel("Right click here");
        label.setBorder(BorderFactory.createEmptyBorder(200, 200, 200, 200));
        label.setComponentPopupMenu(menu);

        JFrame frame = new JFrame("Fading Menu Test");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add(label);
        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(() -> show());
    }
}