基于 jpanel 内容的滚动条

Question

我有一个 500x500 的 jpanel，用作 canvas（在其上绘制）。滚动条（根据需要）在面板上以 510x510 开始（它永远不会在视觉上达到，但会根据内容超过）并且 500x500 表示为 1:1（比例）

下面是一条线的放大图，可以看出，视图 window 保持不变并且没有弹出滚动条，将滚动条设置为始终会导致禁用条。

JScrollPane scrollPanel = new JScrollPane(JPanel,
                ScrollPaneConstants.VERTICAL_SCROLLBAR_AS_NEEDED,
                ScrollPaneConstants.HORIZONTAL_SCROLLBAR_AS_NEEDED);

如何让滚动条读取此面板的内容并变得可滚动？我找不到与此相关的任何内容

附加的面板变大了，但是滚动条没有读取这个变化。是否有某种我需要调用但我没有的更新（考虑一下我没有明确地调用更新？但也找不到与此相关的任何内容）

Answer 1

您需要为您的面板实现可滚动界面，该界面放置在 JScrollPane 中并覆盖方法 getPreferredSize()。这是例子

import java.awt.BorderLayout;
import java.awt.Component;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Rectangle;

import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JList;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.Scrollable;
import javax.swing.WindowConstants;
import javax.swing.plaf.basic.BasicComboBoxRenderer;

public class ZoomPanel extends JPanel implements Scrollable {

    private static final int DEFAULT_SIZE = 500;

    private float zoom = 1f;

    @Override
    public Dimension getPreferredSize() {
        int size = Math.round(zoom * DEFAULT_SIZE);
        return new Dimension(size, size);
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        int size = Math.round(zoom * DEFAULT_SIZE);
        g.drawOval(0, 0, size, size);
    }

    private static class ZoomRenderer extends BasicComboBoxRenderer {

        @Override
        public Component getListCellRendererComponent(JList list, Object value, int index, boolean isSelected, boolean cellHasFocus) {
            Object val = value;
            if (value instanceof Number) {
                val = Math.round(((Number) value).doubleValue() * 100) + "%";
            }
            return super.getListCellRendererComponent(list, val, index, isSelected, cellHasFocus);
        }
    }

    public static void main(String[] args) {
        JFrame frm = new JFrame("Zoom panel");
        ZoomPanel z = new ZoomPanel();
        JScrollPane scroller = new JScrollPane(z);
        Float[] zooms = {.5f, .75f, 1f, 1.5f, 2f, 4f};
        JComboBox<Float> combo = new JComboBox<>(zooms);
        combo.setSelectedIndex(2);
        combo.setRenderer(new ZoomRenderer());
        combo.addActionListener(e -> {
            Float v = (Float) combo.getSelectedItem();
            if (v != null) {
                z.zoom = v;
                scroller.revalidate();
                scroller.repaint();
            }
        });
        JPanel comboPanel = new JPanel();
        comboPanel.add(combo);
        frm.add(comboPanel, BorderLayout.NORTH);
        frm.add(scroller);
        frm.pack();
        frm.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        frm.setLocationRelativeTo(null);
        frm.setVisible(true);
    }

    @Override
    public Dimension getPreferredScrollableViewportSize() {
        return getPreferredSize();
    }

    @Override
    public int getScrollableUnitIncrement(Rectangle visibleRect, int orientation, int direction) {
        return 5;
    }

    @Override
    public int getScrollableBlockIncrement(Rectangle visibleRect, int orientation, int direction) {
        return 20;
    }

    @Override
    public boolean getScrollableTracksViewportWidth() {
        return false;
    }

    @Override
    public boolean getScrollableTracksViewportHeight() {
        return false;
    }
}

基于 jpanel 内容的滚动条

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