java - Swing 中使用 AbstractListModel 的大型虚拟列表——限制为 119,000,000 个项目？

Question

我的“虚拟列表”在 swing 中运行良好，但当我超过某些特定数量的项目时它似乎失败了。 “失败”是指当项目数 > Nmax 时滚动条神奇地消失，当项目数 <= Nmax 时滚动条又回来；在我的系统上，Nmax 似乎在 119,304,000 左右。

我遇到了什么？!？!

(这是一个测试程序:在我的电脑上，如果我输入 119,304 它工作正常，但是我点击向上箭头，滚动条消失了)

package com.example.test;

import java.awt.BorderLayout;
import java.awt.Dimension;
import javax.swing.AbstractListModel;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JList;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JSpinner;
import javax.swing.SpinnerModel;
import javax.swing.SpinnerNumberModel;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;

// based on:
// http://www.java2s.com/Tutorial/Java/0240__Swing/extendsAbstractListModel.htm
// http://www.java2s.com/Tutorial/Java/0240__Swing/SpinnerNumberModel.htm
// http://java.sun.com/j2se/1.4.2/docs/api/javax/swing/SpinnerNumberModel.html
// http://www.java2s.com/Tutorial/Java/0240__Swing/ListeningforJSpinnerEventswithaChangeListener.htm
// http://java.sun.com/products/jfc/tsc/tech_topics/jlist_1/jlist.html

public class BigVirtualList extends JFrame {

    public static void main(String[] args) {
        new BigVirtualList();
    }

    static final int initialLength = 1;
    final private JList list1 = new JList();
    final private BVLData bvldata = new BVLData(initialLength*1000);

    public BigVirtualList() {
        this.setTitle("Big virtual list");
        this.getContentPane().setLayout(new BorderLayout());
        this.setSize(new Dimension(400, 300));
        list1.setModel(bvldata);

        list1.setPrototypeCellValue(list1.getModel().getElementAt(0));


        SpinnerModel model1 = new SpinnerNumberModel(initialLength,1,1000000,1);
        final JSpinner spinner1 = new JSpinner(model1);

        this.getContentPane().add(new JScrollPane(list1), BorderLayout.CENTER);
        JLabel label1 = new JLabel("Length (1000s of items):");
        JPanel panel1 = new JPanel(new BorderLayout());
        panel1.add(label1, BorderLayout.WEST);
        panel1.add(spinner1, BorderLayout.CENTER);
        this.getContentPane().add(panel1, BorderLayout.SOUTH);      

        ChangeListener listener = new ChangeListener() {
            public void stateChanged(ChangeEvent e) {
                Integer newLength = (Integer)spinner1.getValue();
                bvldata.setLength(newLength*1000);
            }
        };

        spinner1.addChangeListener(listener);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setVisible(true);
    }
}

class BVLData extends AbstractListModel {
    public BVLData(int length) { this.length = length; }

    private int length;

    public int getLength() { return length; }
    public void setLength(int length) {
        int oldLength = getLength();
        this.length = length;
        int newLength = getLength();

        if (newLength > oldLength)
            fireIntervalAdded(this, oldLength+1, newLength);
        else if (newLength < oldLength)
            fireIntervalRemoved(this, newLength+1, oldLength);      
    }   

    @Override
    public Object getElementAt(int index) {
        return "Item "+index+" mod 107 = "+(index%107);
    }

    @Override
    public int getSize() { return getLength(); }

}

Answer 1

好吧，我看不出目的，但无论如何......

我猜你打破了滚动 Pane 中某处的整数最大值:

System.out.println("CellHeight:"+list1.getFixedCellHeight());
System.out.println("CellHeight*119304000:"+NumberFormat.getNumberInstance().format(list1.getFixedCellHeight()*119304000.0));
System.out.println("MAXINT:"+Integer.MAX_VALUE);

给你数字:

CellHeight:18CellHeight*119304000:2.147.472.000MAXINT:2.147.483.647

如您所见，再增加 18000 像素的高度将超出 MAXINT ......这会给您带来麻烦。