问题描述

我尝试从 JComboBox 下拉列表中确定每个项目在 JViewPort 中是否可见

I tried to determime for every Items if are or not visible in the JViewPort from JComboBox drop-down list

(我的星期五加班)

我不想为 System.out.print(...) 的重复事件实现 MouseListener

I don't want to implements MouseListener for Repeats events to System.out.print(...)

不可能将 JComboBox 与 JList 一起传递，由 JCombo#Model 使用 SwingUtilities http://www.51sjk.com/Upload/Articles/1/0/341/341573_20230129092401963.html ，但是这个 API 不在我的范围内......

isn't possible pass JComboBox with JList, declared by JCombo#Model by using SwingUtilities http://www.51sjk.com/Upload/Articles/1/0/341/341573_20230129092401963.html , but this APi is out of my...

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class ItemVisibleRecCombo extends JFrame {

    private static final long serialVersionUID = 1L;
    private JComboBox fontsBox;

    public ItemVisibleRecCombo() {
        String[] numbers = {"one", "two", "three", "four", "five", "six", "seven"};
        fontsBox = new JComboBox(numbers);
        fontsBox.setSelectedItem(0);
        fontsBox.addItemListener(new ItemListener() {

            @Override
            public void itemStateChanged(ItemEvent e) {
                if (e.getStateChange() == ItemEvent.SELECTED) {
                    manItemInCombo();
                }
            }
        });
        fontsBox.setModel(new DefaultComboBoxModel(numbers));
        fontsBox.setMaximumRowCount(3);
        add(fontsBox, BorderLayout.CENTER);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setPreferredSize(new Dimension(400, 60));
        setLocation(200, 105);
        pack();
        setVisible(true);
    }

    private void manItemInCombo() {
        if (fontsBox.getItemCount() > 0) {
            final Object comp = fontsBox.getUI().getAccessibleChild(fontsBox, 0);
            if ((comp instanceof JPopupMenu)) {
                final JList list = new JList(fontsBox.getModel());
                final JPopupMenu popup = (JPopupMenu) comp;
                final JScrollPane scrollPane = (JScrollPane) popup.getComponent(0);
                final JViewport viewport = scrollPane.getViewport();
                final Rectangle rect = popup.getVisibleRect();
                Point pt = viewport.getViewPosition();
                for (int i = 0; i < list.getModel().getSize(); i++) {
                    pt = list.indexToLocation(i);
                    System.out.print(pt + " - ");
                    rect.setLocation(rect.x - pt.x, rect.y - pt.y);
                    System.out.println(new Rectangle(viewport.getExtentSize()).contains(rect));
                }
            }
        }
    }

    public static void main(String arg[]) {
        java.awt.EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {
                ItemVisibleRecCombo ivrc = new ItemVisibleRecCombo();
            }
        });
    }
}

推荐答案

基本上，您正在寻找 list.locationToIndex (如果我理解正确的话)，类似

Basically, you'r looking for list.locationToIndex (if I understood you correctly), something like

    Accessible a = fontsBox.getUI().getAccessibleChild(fontsBox, 0);
    if (a instanceof javax.swing.plaf.basic.ComboPopup) {
        JList list = ((javax.swing.plaf.basic.ComboPopup)a).getList();
        Rectangle rect = list.getVisibleRect();
        int first = list.locationToIndex(rect.getLocation());
        // similar for last, at the lower edge of the visible rect, left as exercise <g>
        // Edit: as of @Boro's comment, last is easier calculated with maxRowCount
        int last = first + fontsBox.getMaximumRowCount() - 1;
        ....

顺便说一句，另一个未传递到列表中的属性:本来可以预期

BTW, yet another property that's not passed on to the list: would have expected

   list.getVisibleRowCount() == combo.getMaximumRowCount()   

回答这个问题:第一个/最后一个之间的所有项目(包括在内)都是可见的，第一个上方和最后一个下方的所有项目都不可见；-)

To answer the question: all items between first/last, inclusively, are visible, all items above first and below last not visible ;-)