如何禁用 JScrollPane 上滚轮滚动事件的默认绘画行为

Question

我最近购买了Filthy Rich Clients这本书，我发现它非常有用且有趣。 基于书中的一个示例，我尝试实现一个自定义 ScrollPane，它在要显示的组件的视图底部显示一个“阴影”。 我最终得到了下面的代码。 它有效，但并不完美。 特别是当我通过拖动滚动条滚动窗格时，一切正常，并且绘画非常流畅。 但是当我用鼠标滚动时，阴影会闪烁，我不知道为什么。 谁能帮我？

编辑：滚动窗格中的任何组件都会发生同样的情况。 编辑代码以显示两个框架来查看问题。

编辑 2：我已将问题与滚动窗格处理鼠标滚轮事件的方式隔离开来。 滚动时，滚动窗格会根据滚动方向稍微向上或向下复制视口的内容，然后绘制进入视图的区域。 我的代码使整个组件变得“脏”，但那是在组件转移内容之后。 因此，您会暂时看到“阴影”渐变不合适，直到发出重新绘制为止。 关于如何禁用此功能有什么想法吗？

import java.awt.AlphaComposite;
import java.awt.Color;
import java.awt.Container;
import java.awt.GradientPaint;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import java.awt.image.BufferedImage;

import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTable;
import javax.swing.JTextArea;
import javax.swing.RepaintManager;

public class Test {

    public static void main(String[] args) {
        JFrame f = new JFrame("Table");
        JFrame f1 = new JFrame("Text Area");
        Object[] names = new Object[] { "Title", "Artist", "Album" };
        String[][] data = new String[][] {
                { "Los Angeles", "Sugarcult", "Lights Out" },
                { "Do It Alone", "Sugarcult", "Lights Out" },
                { "Made a Mistake", "Sugarcult", "Lights Out" },
                { "Kiss You Better", "Maximo Park", "A Certain Trigger" },
                { "All Over the Shop", "Maximo Park", "A Certain Trigger" },
                { "Los Angeles", "Sugarcult", "Lights Out" },
                { "Do It Alone", "Sugarcult", "Lights Out" },
                { "Made a Mistake", "Sugarcult", "Lights Out" },
                { "Kiss You Better", "Maximo Park", "A Certain Trigger" },
                { "All Over the Shop", "Maximo Park", "A Certain Trigger" },
                { "Los Angeles", "Sugarcult", "Lights Out" },
                { "Do It Alone", "Sugarcult", "Lights Out" },
                { "Made a Mistake", "Sugarcult", "Lights Out" },
                { "Kiss You Better", "Maximo Park", "A Certain Trigger" },
                { "All Over the Shop", "Maximo Park", "A Certain Trigger" },
                { "Los Angeles", "Sugarcult", "Lights Out" },
                { "Do It Alone", "Sugarcult", "Lights Out" },
                { "Made a Mistake", "Sugarcult", "Lights Out" },
                { "Kiss You Better", "Maximo Park", "A Certain Trigger" },
                { "All Over the Shop", "Maximo Park", "A Certain Trigger" },
                { "Los Angeles", "Sugarcult", "Lights Out" },
                { "Do It Alone", "Sugarcult", "Lights Out" },
                { "Made a Mistake", "Sugarcult", "Lights Out" },
                { "Kiss You Better", "Maximo Park", "A Certain Trigger" },
                { "All Over the Shop", "Maximo Park", "A Certain Trigger" },
                { "Going Missing", "Maximo Park", "A Certain Trigger" } };
        JTable table = new JTable(data, names);
        f.getContentPane().add(new ShadowScrollPane(table));
        f1.getContentPane().add(new ShadowScrollPane(new JTextArea(20, 50)));
        RepaintManager.setCurrentManager(new RepaintManager(){
            @Override
            public void addDirtyRegion(JComponent c, int x, int y, int w, int h) {
                Container con = c.getParent();
                while (con instanceof JComponent) {
                    if (!con.isVisible()) {
                        return;
                    }
                    if (con instanceof ShadowScrollPane ) {
                        c = (JComponent)con;
                        x = 0;
                        y = 0;
                        w = con.getWidth();
                        h = con.getHeight();
                    }
                    con = con.getParent();
                }
                super.addDirtyRegion(c, x, y, w, h);
            }
        });
        f.pack();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setVisible(true);
        f1.pack();
        f1.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f1.setVisible(true);
    }

}

@SuppressWarnings("serial")
class ShadowScrollPane extends JScrollPane {

    private final int h = 50;
    private BufferedImage img = null;
    private BufferedImage shadow = new BufferedImage(1, h, BufferedImage.TYPE_INT_ARGB);

    public ShadowScrollPane(JComponent com) {
        super(com);
        Graphics2D g2 = shadow.createGraphics();
        g2.setPaint(new Color(50, 50, 50));
        g2.fillRect(0, 0, 1, h);
        g2.setComposite(AlphaComposite.DstIn);
        g2.setPaint(new GradientPaint(0, 0, new Color(0, 0, 0, 0f), 0, h, new Color(1, 1, 1, 0.6f)));
        g2.fillRect(0, 0, 1, h);
        g2.dispose();
    }

    @Override
    public void paint(Graphics g) {
        if (img == null || img.getWidth()!=getWidth() || img.getHeight() != getHeight()) {
            img = new BufferedImage(getWidth(), getHeight(), BufferedImage.TYPE_INT_ARGB);
        }
        Graphics2D g2 = img.createGraphics();
        super.paint(g2);
        Rectangle bounds = getViewport().getVisibleRect();
        g2.scale(bounds.getWidth(), -1);
        int y = (getColumnHeader()==null)?0:getColumnHeader().getHeight();
        g2.drawImage(shadow, bounds.x, -bounds.y - y-h, null);
        g2.scale(1,-1);
        g2.drawImage(shadow, bounds.x, bounds.y + bounds.height-h+y, null);
        g2.dispose();
        g.drawImage(img, 0, 0, null);
    }
}

Answer 1

您是否尝试过在 ScrollPane 对象上调用 setWheelScrollingEnabled(false) ？

来自javadoc：

启用/禁用滚动
对鼠标移动的响应
车轮。 滚轮滚动通过以下方式启用
默认。

根据 Savvas 的评论进行更新如下。

也许视口上的“setScrollMode(int)”方法可以帮助您。 此方法将确定 swing 如何滚动视口。

您可以使用 getViewPort() 方法直接从 ScrollPane 获取视口。
您有以下选择：

BLIT_SCROLL_MODE
BACKINGSTORE_SCROLL_MODE
SIMPLE_SCROLL_MODE

根据 javadoc BLIT_SCROLL_MODE 将使用 Graphics.copyArea，因此也许可以尝试其他选项之一。