JComboBox 确定项目是否在下拉列表中可见/不可见答案

【问题标题】：JComboBox determine if Items are/aren't visible in drop-down listJComboBox 确定项目是否在下拉列表中可见/不可见
【发布时间】：2011-08-20 04:35:19
【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

（我的星期五加班）

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

不可能将 JComboBox 与 JList 一起传递，由 JCombo#Model 使用 SwingUtilities http://download.oracle.com/javase/6/docs/api/javax/swing/SwingUtilities.html 声明，但这个 APi 不在我的范围内......

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();
            }
        });
    }
}

【问题讨论】：

标签： java swing popup jcombobox viewport

【解决方案1】：

谢谢，但你的假设不正确，这里是输出，我仍然无法测试 ViewPort 是否正确包含 Item，没办法，我必须回到我原来的声明，因为正确显示第一个可见 Item呸呸呸

编辑感谢@Anthony Accioly 的正确建议Changing the listener from ItemListener to ActionListener

ItemListener 输出错误

1stIndex = 0, LastIndex = 2, SelectedItem1 = two, Value = one, two, three//ok
1stIndex = 0, LastIndex = 2, SelectedItem1 = three, Value = one, two, three//ok
1stIndex = 0, LastIndex = 2, SelectedItem1 = four, Value = one, two, three//wrong
1stIndex = 1, LastIndex = 3, SelectedItem1 = five, Value = two, three, four//wrong
1stIndex = 2, LastIndex = 4, SelectedItem1 = six, Value = three, four, five//wrong
1stIndex = 3, LastIndex = 5, SelectedItem1 = seven, Value = four, five, six//wrong
1stIndex = 4, LastIndex = 6, SelectedItem1 = six, Value = five, six, seven//ok
1stIndex = 4, LastIndex = 6, SelectedItem1 = five, Value = five, six, seven//ok
1stIndex = 4, LastIndex = 6, SelectedItem1 = four, Value = five, six, seven//wrong
1stIndex = 3, LastIndex = 5, SelectedItem1 = three, Value = four, five, six//wrong
1stIndex = 2, LastIndex = 4, SelectedItem1 = two, Value = three, four, five//wrong
1stIndex = 1, LastIndex = 3, SelectedItem1 = one, Value = two, three, four//wrong

以及来自ActionListener 的预期输出

1stIndex = 0, LastIndex = 2, SelectedItem1 = two, Value = one, two, three
1stIndex = 0, LastIndex = 2, SelectedItem1 = three, Value = one, two, three
1stIndex = 1, LastIndex = 3, SelectedItem1 = four, Value = two, three, four
1stIndex = 2, LastIndex = 4, SelectedItem1 = five, Value = three, four, five
1stIndex = 3, LastIndex = 5, SelectedItem1 = six, Value = four, five, six
1stIndex = 4, LastIndex = 6, SelectedItem1 = seven, Value = five, six, seven
1stIndex = 4, LastIndex = 6, SelectedItem1 = six, Value = five, six, seven
1stIndex = 4, LastIndex = 6, SelectedItem1 = five, Value = five, six, seven
1stIndex = 3, LastIndex = 5, SelectedItem1 = four, Value = four, five, six
1stIndex = 2, LastIndex = 4, SelectedItem1 = three, Value = three, four, five
1stIndex = 1, LastIndex = 3, SelectedItem1 = two, Value = two, three, four
1stIndex = 0, LastIndex = 2, SelectedItem1 = one, Value = one, two, three

修改后的代码

import java.awt.*;
import java.awt.event.*;
import javax.accessibility.Accessible;
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.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {
                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 Accessible a = fontsBox.getUI().getAccessibleChild(fontsBox, 0);
            if (a instanceof javax.swing.plaf.basic.ComboPopup) {
                final JList list = ((javax.swing.plaf.basic.ComboPopup) a).getList();
                final Rectangle rect = list.getVisibleRect();
                final int first = list.locationToIndex(rect.getLocation());
                final int last = first + fontsBox.getMaximumRowCount() - 1;
                String selectedItem = fontsBox.getSelectedItem().toString();
                System.out.println("1stIndex = " + first + ", LastIndex = "
                        + last + ", SelectedItem1 = " + selectedItem
                        + ", Value = " + fontsBox.getItemAt(first).toString()
                        + ", " + fontsBox.getItemAt(first + 1).toString()
                        + ", " + fontsBox.getItemAt(first + 2).toString());
            }
        }
    }

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

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

【讨论】：

对我来说只是一个评论（Windows + Java SE 6），单击项目似乎给出了正确的结果，使用箭头我得到了错误的结果。 @mKorbel，你能确认一下吗？
是的，这是正确的，:-) 但是直接选择某些项目并不让我感兴趣，因为 ItemListener 只是对 MouseListener 的模拟，然后如果您通过 Mouse + ScroolBar 滚动，则不会选择任何项目:-)
好的。但是在什么样的事件中，您究竟想捕捉可见的行？鼠标进入？鼠标退出？鼠标移动了？
@Anthony Accioly，现在我不知道可能直接((JViewport) ((JScrollPane) ((BasicComboPopup) field.get(box.getUI())).getComponents()[0]).getComponents()[0]).getComponents()[0].addMouseListener(listener()); 可能是普通的香草听众fontsBox.addMouseListener blablabla MouseAdapter 但在我的 TZ 中睡过了午夜

【解决方案2】：

将侦听器从 ItemListener 更改为 ActionListener 似乎给出了预期的结果，无论是箭头键还是点击：

fontsBox.addActionListener(new ActionListener() {

    @Override
    public void actionPerformed(ActionEvent e) {
         manItemInCombo();
    }
});

【讨论】：

【解决方案3】：

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

    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

   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；-)

【讨论】：

是的，仅此线程 stackoverflow.com/questions/5896282/… 是唯一的，因为我想为派生的 JViewPort 中可见的项目使用/应用渲染器，我会检查你的...
+1 更好更干净的做事方式。 @kleopatra 虽然要获得最后一个，但最好只计算它而不是向列表询问您需要为其创建新对象的位置。 int rowCount = fontsBox.getMaximumRowCount(); int last = first + (rowCount-1);
@Boro - 不是第一个：只需移动可见矩形，无需创建（没关系，假设微优化;-) +1 用于使用 maxRowCount，将编辑：- )
你是完全正确的我忘记了可见的矩形是一个副本，你可以用它做你想做的一切。谢谢你。

【解决方案4】：

如果要获取组合框中可见的元素，我在这里有一个算法可供您使用

                Point pt = viewport.getViewPosition();
                int rowCount = fontsBox.getMaximumRowCount();
                int rowsize = viewport.getSize().height / rowCount;
                System.out.println("viewport.getHeight()="+ viewport.getHeight()
                        +"; viewport.getViewSize().getHeight()="+ viewport.getViewSize().getHeight()
                        +"; rowsize=" + rowsize+"; pt="+pt);                
                int firstVisibleElementIndex = pt.y/rowsize;
                int lastVisibleElementIndex = firstVisibleElementIndex + (rowCount-1);
                System.out.println("firstVisibleElementIndex="+ firstVisibleElementIndex
                        +"; lastVisibleElementIndex="+lastVisibleElementIndex);

检查一下，它会返回第一个和最后一个可见元素，然后由你决定对它们做什么。

编辑：这只是在给定示例之上构建的一个快速（且令人讨厌的）解决方案。如需更好的解决方案，请参阅@kleopatra 的解决方案。

【讨论】：

不，你不需要视口，列表本身会告诉你所有必要的
@kleopatra 我刚刚扩展了@mKorbel 提供的示例，我并不是说这是最好/唯一的方法:)
不要重复错误/过分复杂的事情，它们容易留在记忆中;-)
@kleopatra 你是完全正确的。 :) 实施我的解决方案我不考虑哪种是“更清洁”的方法，我只是重用了代码。