如何禁用JComboBox中的某些项目

Question

我有一个ComboBox我有8个项目,其中我想要显示所有但在某个条件下,用户应该只能选择前两个,所以我已经编程,如果条件为真,用户选择任何其他选项,然后显示消息框显示"You cannot choose this",然后自动选择默认值.到现在为止还挺好.

但现在的问题是用户无法通过查看JComboBox可以选择的选项来确定,所以我想要做的是,如果条件为真,那么除了前两个选项之外的所有选项都应该被禁用(或者灰色或其他东西),以便用户可以知道你无法选择它,如果他们仍然这样做,那么我的消息框应该出现.

我尝试了什么:我试着查看这个,但我无法弄清楚问题中做了什么(它的答案对我没有用),我也尝试了其他选择,但没有成功.

注意:我正在使用Netbeans GUI来创建所有内容,我正在编写的代码已经开启JComboBoxActionPerformed,我是一个新手,所以我无法弄清楚自己,为此道歉

Answer 1

首先...

这将需要一些手动编码.GUI Builder不会帮助你.

至于渲染......

您可以实现自己的BasicComboBoxRenderer,在其中传递给它ListSelectionModel.根据您传递给它的模型,只有选定的间隔将使用标准渲染器进行渲染.通过更改前景色及其选择背景,剩余索引将以禁用方式呈现.

^{注意:这只会影响项目的呈现,而不会影响实际的选择事件}

import java.awt.Color;
import java.awt.Component;
import javax.swing.JList;
import javax.swing.ListSelectionModel;
import javax.swing.UIManager;
import javax.swing.plaf.basic.BasicComboBoxRenderer;

public class EnabledComboBoxRenderer extends BasicComboBoxRenderer {

    private ListSelectionModel enabledItems;

    private Color disabledColor = Color.lightGray;

    public EnabledComboBoxRenderer() {}

    public EnabledComboBoxRenderer(ListSelectionModel enabled) {
        super();
        this.enabledItems = enabled;
    }

    public void setEnabledItems(ListSelectionModel enabled) {
        this.enabledItems = enabled;
    }

    public void setDisabledColor(Color disabledColor) {
        this.disabledColor = disabledColor;
    }

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

        Component c = super.getListCellRendererComponent(list, value, index,
                isSelected, cellHasFocus);

        if (!enabledItems.isSelectedIndex(index)) {// not enabled
            if (isSelected) {
                c.setBackground(UIManager.getColor("ComboBox.background"));
            } else {
                c.setBackground(super.getBackground());
            }

            c.setForeground(disabledColor);

        } else {
            c.setBackground(super.getBackground());
            c.setForeground(super.getForeground());
        }
        return c;
    }
}

至于选择项目......

您可以使用两个单独的侦听器.一个用于启用项目,一个用于禁用项目.启用项目后,您可以1.更改选择模型2.添加启用的侦听器3.删除已禁用的侦听器

private class EnabledListener implements ActionListener {
    @Override
    public void actionPerformed(ActionEvent e) {
        System.out.println(((JComboBox) e.getSource()).getSelectedItem());
    }
}

private class DisabledListener implements ActionListener {
    @Override
    public void actionPerformed(ActionEvent e) {
        if (((JComboBox) e.getSource()).getSelectedIndex() != SELECTION_INTERVAL[0]
                && ((JComboBox) e.getSource()).getSelectedIndex() != SELECTION_INTERVAL[1]) {
            JOptionPane.showMessageDialog(null,
                    "You can't Select that Item", "ERROR",
                    JOptionPane.ERROR_MESSAGE);
        } else {
            System.out.println(((JComboBox) e.getSource())
                    .getSelectedItem());
        }
    }
}

protected void enableItemsInComboBox() {
    comboBox.removeActionListener(disabledListener);
    comboBox.addActionListener(enabledListener);
    model.setSelectionInterval(SELECTION_INTERVAL[0], comboBox.getModel()
        .getSize() - 1);
}

反之亦然

protected void disableItemsInComboBox() {
    comboBox.removeActionListener(enabledListener);
    comboBox.addActionListener(disabledListener);
    model.setSelectionInterval(SELECTION_INTERVAL[0], SELECTION_INTERVAL[1]);
}

这是一个完整的运行示例,使用EnabledComboBoxRenderer从上面开始

import java.awt.GridBagLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;

import javax.swing.DefaultListSelectionModel;
import javax.swing.JCheckBox;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.SwingUtilities;

public class ComboBoxDisabledItemsDemo {
    private static final int[] SELECTION_INTERVAL = { 0, 1 };

    private JComboBox comboBox;
    private JCheckBox disableCheckBox;
    private DefaultListSelectionModel model = new DefaultListSelectionModel();
    private EnabledComboBoxRenderer enableRenderer = new EnabledComboBoxRenderer();

    private EnabledListener enabledListener = new EnabledListener();
    private DisabledListener disabledListener = new DisabledListener();

    public ComboBoxDisabledItemsDemo() {
        comboBox = createComboBox();

        disableCheckBox = createCheckBox();
        disableCheckBox.setSelected(true); // this adds the action listener to
                                            // the
                                            // to the combo box

        JFrame frame = new JFrame("Disabled Combo Box Items");
        frame.setLayout(new GridBagLayout());
        frame.add(comboBox);
        frame.add(disableCheckBox);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(300, 300);
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    private JComboBox createComboBox() {
        String[] list = { "Item 1", "Item 2", "Item 3", "Item 4", "Item 5",
                "Item 6", "Item 7" };
        JComboBox cbox = new JComboBox(list);
        model.addSelectionInterval(SELECTION_INTERVAL[0], SELECTION_INTERVAL[1]);
        enableRenderer.setEnabledItems(model);
        cbox.setRenderer(enableRenderer);
        return cbox;
    }

    private class EnabledListener implements ActionListener {
        @Override
        public void actionPerformed(ActionEvent e) {
            System.out.println(((JComboBox) e.getSource()).getSelectedItem());
        }
    }

    private class DisabledListener implements ActionListener {
        @Override
        public void actionPerformed(ActionEvent e) {
            if (((JComboBox) e.getSource()).getSelectedIndex() != SELECTION_INTERVAL[0]
                    && ((JComboBox) e.getSource()).getSelectedIndex() != SELECTION_INTERVAL[1]) {
                JOptionPane.showMessageDialog(null,
                        "You can't Select that Item", "ERROR",
                        JOptionPane.ERROR_MESSAGE);
            } else {
                System.out.println(((JComboBox) e.getSource())
                        .getSelectedItem());
            }
        }
    }

    protected void disableItemsInComboBox() {
        comboBox.removeActionListener(enabledListener);
        comboBox.addActionListener(disabledListener);
        model.setSelectionInterval(SELECTION_INTERVAL[0], SELECTION_INTERVAL[1]);
    }

    protected void enableItemsInComboBox() {
        comboBox.removeActionListener(disabledListener);
        comboBox.addActionListener(enabledListener);
        model.setSelectionInterval(SELECTION_INTERVAL[0], comboBox.getModel()
                .getSize() - 1);
    }

    private JCheckBox createCheckBox() {
        JCheckBox checkBox = new JCheckBox("diabled");
        checkBox.addItemListener(new ItemListener() {
            public void itemStateChanged(ItemEvent e) {
                if (e.getStateChange() == ItemEvent.SELECTED) {
                    disableItemsInComboBox();
                } else if (e.getStateChange() == ItemEvent.DESELECTED) {
                    enableItemsInComboBox();
                }
            }
        });
        return checkBox;
    }

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