创建一个带有多个复选框的组合框

Question

我已阅读文档和教程，并在此处搜索，但无济于事。

Oracle tutorial: how to use custom render for ComboBox

Another question similar with a somehow vague answer

我认为这很重要，因为很多人都问过这个问题，但没有人能提供一个简单、可行的例子。所以我必须自己问：

我们如何制作一个带有下拉菜单的组合框，让我们可以选择多个选项？

什么不工作：

• JList 在这里被证明是没用的，因为我不能让它出现在下拉菜单中。
• Swing 中没有 CheckBoxList。

我已经在组合的下拉菜单中使用复选框进行了 SCCEE，但复选框拒绝被选中，复选框中的复选框丢失。

我们怎样才能做到这一点？

import java.awt.Component;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.FocusEvent;
import java.awt.event.FocusListener;
import java.util.List;

import javax.swing.DefaultCellEditor;
import javax.swing.DefaultListModel;
import javax.swing.DefaultListSelectionModel;
import javax.swing.JCheckBox;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JList;
import javax.swing.JPanel;
import javax.swing.JTable;
import javax.swing.ListCellRenderer;
import javax.swing.ListSelectionModel;
import javax.swing.SwingUtilities;
import javax.swing.event.ListSelectionEvent;
import javax.swing.event.ListSelectionListener;
import javax.swing.table.TableColumn;

public class ComboOfCheckBox extends JFrame {

public ComboOfCheckBox() {
    begin();
}

private void begin() {
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    JPanel panel = new JPanel();

    JTable table = new JTable(new Object[2][2], new String[]{"COL1", "COL2"});
    final JCheckBox chx1 = new JCheckBox("Oh");
    final JCheckBox chx2 = new JCheckBox("My");
    final JCheckBox chx3 = new JCheckBox("God");
    String[] values = new String[] {"Oh", "My", "God"};
    JCheckBox[] array = new JCheckBox[] {chx1, chx2, chx3};
    final JComboBox<JCheckBox> comboBox = new JComboBox<JCheckBox>(array) {
        @Override
        public void setPopupVisible(boolean visible){
            if (visible) {
                super.setPopupVisible(visible);
            }
        }
    };

    class CheckBoxRenderer  implements ListCellRenderer {

        private boolean[] selected;
        private String[] items;

        public CheckBoxRenderer(String[] items) {
            this.items = items;
            this.selected = new boolean[items.length];
        }

        @Override
        public Component getListCellRendererComponent(JList list, Object value, int index, boolean isSelected,
                boolean cellHasFocus) {
            JLabel label = null;
            JCheckBox box = null;
            if (value instanceof JCheckBox) {
                label = new JLabel(((JCheckBox)value).getText());
                box = new JCheckBox(label.getText());
            }
            return box;
        }
        public void setSelected(int i, boolean selected) {
            this.selected[i] = selected;
        }

    }

    comboBox.setRenderer(new CheckBoxRenderer(values));

    panel.add(comboBox);    
    panel.add(new JCheckBox("Another"));
    getContentPane().add(panel);
    pack();
    setVisible(true);
}

public static void main(String[] args) {
    SwingUtilities.invokeLater(new Runnable() {

        @Override
        public void run() {
            ComboOfCheckBox frame = new ComboOfCheckBox();

        }   
    });
}
}

Answer 1

这里有一个部分答案。它没有解决弹出窗口上的 ComboBox 屏蔽事件的问题，但它确实可以解决这个问题。问题仍然是 ComboBox 将一个项目上的每个选择视为另一个项目上的取消选择。但是，您面临的一个问题是，由于每次重绘时都会调用渲染器，因此您的复选框不是持久的 - Map 解决了这个问题。

public class ComboOfCheckBox extends JFrame {

public ComboOfCheckBox() {
    begin();
}

private void begin() {
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    JPanel panel = new JPanel();

    JTable table = new JTable(new Object[2][2], new String[]{"COL1", "COL2"});
    String[] values = new String[] {"Oh", "My", "God"};
    final JComboBox<String> comboBox = new JComboBox<String>(values) {
        @Override
        public void setPopupVisible(boolean visible){
            if (visible) {
                super.setPopupVisible(visible);
            }
        }
    };

    class CheckBoxRenderer  implements ListCellRenderer<Object> {
        private Map<String, JCheckBox> items = new HashMap<>();
        public CheckBoxRenderer(String[] items) {
            for (String item : items) {
                JCheckBox box = new JCheckBox(item);
                this.items.put(item, box);
            }

        }
        @Override
        public Component getListCellRendererComponent(JList<?> list, Object value, int index, boolean isSelected,
                                                      boolean cellHasFocus) {
            if (items.containsKey(value)) {
                return items.get(value);
            } else {
                return null;
            }
        }

        public void setSelected(String item, boolean selected) {
            if (item.contains(item)) {
                JCheckBox cb = items.get(item);
                cb.setSelected(selected);
            }
        }
    }

    final CheckBoxRenderer renderer = new CheckBoxRenderer(values);

    comboBox.setRenderer(renderer);
    comboBox.addItemListener(e -> {
        String item = (String) e.getItem();
        if (e.getStateChange() == ItemEvent.DESELECTED) {
            renderer.setSelected(item, false);
        } else {
            renderer.setSelected(item, true);
        }
    });

    panel.add(comboBox);

    panel.add(new JCheckBox("Another"));
    getContentPane().add(panel);
    pack();
    setVisible(true);
}
public static void main(String[] args) {
    SwingUtilities.invokeLater(new Runnable() {

        @Override
        public void run() {
            ComboOfCheckBox frame = new ComboOfCheckBox();

        }

    });
}

}

Answer 2

我也找到了解决方法，但使用 ActionListener。事实是，您不能在JCheckBox 上直接监听，因为渲染每个周期都会创建一个新的，而 Piotr Wilkin 的解决方法解决了这个问题。您也可以使用此解决方案，在单击 JComboBox 时检查鼠标的位置：

    comboBox.addActionListener(new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {
            JComboBox combo = (JComboBox) e.getSource();
            int y = MouseInfo.getPointerInfo().getLocation().y - combo.getLocationOnScreen().y;
            int item =  y / combo.getHeight();
            ((CheckBoxRenderer) combo.getRenderer()).selected[item] = !((CheckBoxRenderer) combo.getRenderer()).selected[item];
        }
    });

另外，在getListCellRendererComponent 方法中，您需要检查index >= 0，因为当第一次创建渲染器时，它会抛出错误，因为selected 数组为空。 :)

Answer 3

您忘记了与您的组合框关联的动作侦听器。另一方面，每次选择其他项目时都会调用CheckBoxRenderer，因此如果您将JCheckBox 对象作为JComboBox 项目您必须从外部更改其状态（选中或不选中），这意味着从方法调用组合框的动作监听器。但是你可以使用CheckBoxRenderer的自动调用，这里我做了一个简单的代码来教你怎么做：

public class ComboOfChechBox extends JFrame {

    public ComboOfChechBox() {
        begin();
    }

    //a custom item for comboBox
    public class CustomerItem {

        public String label;
        public boolean status;

        public CustomerItem(String label, boolean status) {
            this.label = label;
            this.status = status;
        }
    }

    //the class that implements ListCellRenderer
    public class RenderCheckComboBox implements ListCellRenderer {

        //a JCheckBox is associated for one item
        JCheckBox checkBox;

        Color selectedBG = new Color(112, 146, 190);

        public RenderCheckComboBox() {
            this.checkBox = new JCheckBox();
        }

        @Override
        public Component getListCellRendererComponent(JList list, Object value, int index, boolean isSelected,
                boolean cellHasFocus) {

            //recuperate the item value
            CustomerItem value_ = (CustomerItem) value;

            if (value_ != null) {
                //put the label of item as a label for the associated JCheckBox object
                checkBox.setText(value_.label);

                //put the status of item as a status for the associated JCheckBox object
                checkBox.setSelected(value_.status);
            }

            if (isSelected) {
                checkBox.setBackground(Color.GRAY);
            } else {
                checkBox.setBackground(Color.WHITE);
            }
            return checkBox;
        }

    }

    private void begin() {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        JPanel panel = new JPanel();

        JComboBox<CustomerItem> combo = new JComboBox<CustomerItem>() {
            @Override
            public void setPopupVisible(boolean visible) {
                if (visible) {
                    super.setPopupVisible(visible);
                }
            }
        };

        CustomerItem[] items = new CustomerItem[3];
        items[0] = new CustomerItem("oh", false);
        items[1] = new CustomerItem("My", false);
        items[2] = new CustomerItem("God", false);
        combo.setModel(new DefaultComboBoxModel<CustomerItem>(items));
        combo.setRenderer(new RenderCheckComboBox());

        //the action listener that you forget
        combo.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent ae) {
                CustomerItem item = (CustomerItem) ((JComboBox) ae.getSource()).getSelectedItem();
                item.status = !item.status;

                // update the ui of combo
                combo.updateUI();

                //keep the popMenu of the combo as visible
                combo.setPopupVisible(true);
            }
        });
        panel.add(combo);
        panel.add(new JCheckBox("Another"));
        getContentPane().add(panel);
        pack();
        setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {

            @Override
            public void run() {
                new ComboOfChechBox();
            }
        });
    }
}