Question

我有以下情况：在JCombobox中，首选大小基于最大的项目大小。但是，此计算不考虑为null呈现的值。它只关心模型中的值。因此，当渲染空值的文本大于另一个元素时，标签会被截断，并且我在末尾有三个点（...）。我想避免这种情况。

这是我正在谈论的一个小演示：

Truncated null value rendered

import java.awt.Component;
import java.awt.GridBagLayout;

import javax.swing.DefaultListCellRenderer;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JList;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class TestComboBox {

    protected void initUI() {
        JFrame frame = new JFrame(TestComboBox.class.getSimpleName());
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        JPanel panel = new JPanel(new GridBagLayout());
        JComboBox comboBox = new JComboBox(new Object[] { "Something", "Stuff", "Beep" });
        comboBox.setRenderer(new DefaultListCellRenderer() {
            @Override
            public Component getListCellRendererComponent(JList<?> list, Object value, int index, boolean isSelected, boolean cellHasFocus) {
                Component comp = super.getListCellRendererComponent(list, value, index, isSelected, cellHasFocus);
                if (value == null) {
                    setText("No selection");
                }
                return comp;
            }
        });
        comboBox.setSelectedItem(null);
        panel.add(comboBox);
        frame.add(panel);
        frame.setSize(200, 100);
        frame.setVisible(true);
    }

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

            @Override
            public void run() {
                new TestComboBox().initUI();
            }
        });
    }
}

我想知道你是否有任何建议。到目前为止，我的想法是扩展JComboBox，覆盖首选大小，还执行null值的呈现，并将调用的最大维度带到super.preferredSize和空值呈现之一。但我发现这有点令人失望。

我真的不想使用prototypeDisplayValue ~~绝对不是一个选项，因为我不知道该下拉列表中的值~~。

Answer 1

我将利用这样一个事实：我们知道从Component返回的DefaultListCellRenderer.getListCellRendererComponent是DefaultListCellRenderer对象本身，并且它是{{1}的实例}}

我还假设您的外观以常规方式计算组合框的首选大小，类似于JLabel。

有了这些信息，这个解决方案可能很丑陋且效率低下，但它确实有效：

BasicComboBoxUI

Answer 2

我没有在代码中对此进行测试，但我的方法是：

确定渲染器返回的preferredSize Component与preferredSize的实际JComboBox之间的差异。不是通过使用任何硬编码值，而只是通过创建仅包含一个项目和已知渲染器的幕后JComboBox，并将JComboBox的首选大小与大小相比较已知渲染器返回的Component。
每次通过将聆听者附加到UIManager
覆盖实际getPreferredSize的{{1}}并返回JComboBox和super.getPreferredSize()

这应该处理“外观”问题，避免不必要的计算，您可以轻松创建包含此功能的getPreferredSize( rendererComponent ) + calculatedDifference扩展名。

Answer 3

所以这就是我到目前为止所得到的，但一个主要问题是交叉L＆amp; F问题。另一种方法是遍历ComboBox模型的所有值和值“No selection”，并检查哪一个是最长的。然后我可以将它设置为prototypeDisplayValue。问题是我需要一个图形上下文来测量每个字符串的边界。

以下是我们在@Enwired和@Robin中找到的2个解决方案。感谢他们两人。

编辑：在与@Robin讨论后，我发现这个解决方案实际上更简单，适用于所有平台和外观。唯一的缺点是我们需要创建一个额外的JComboBox。

import java.awt.Component;
import java.awt.Dimension;
import java.awt.GridBagLayout;

import javax.swing.DefaultListCellRenderer;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JList;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import javax.swing.UnsupportedLookAndFeelException;

public class TestComboBox {

    protected void initUI() {
        JFrame frame = new JFrame(TestComboBox.class.getSimpleName());
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        JPanel panel = new JPanel(new GridBagLayout());
        JComboBox comboBox = new JComboBox(new Object[] { "Something", "Stuff", "Beep" }) {

            private JComboBox internal;

            private JComboBox getInternalComboBox() {
                if (internal == null) {
                    internal = new JComboBox(new Object[] { null });
                }
                return internal;
            }

            @Override
            public Dimension getPreferredSize() {
                Dimension preferredSize = super.getPreferredSize();
                if (getSelectedItem() == null) {
                    getInternalComboBox().setRenderer(getRenderer());
                    Dimension nullDimension = getInternalComboBox().getPreferredSize();
                    preferredSize.width = Math.max(preferredSize.width, nullDimension.width);
                    preferredSize.height = Math.max(preferredSize.height, nullDimension.height);
                }
                return preferredSize;
            }

            @Override
            public void updateUI() {
                internal = null;
                super.updateUI();
            }
        };
        comboBox.setRenderer(new DefaultListCellRenderer() {
            @Override
            public Component getListCellRendererComponent(JList list, Object value, int index, boolean isSelected, boolean cellHasFocus) {
                Component comp = super.getListCellRendererComponent(list, value, index, isSelected, cellHasFocus);
                if (value == null) {
                    setText("No selection");
                }
                return comp;
            }
        });
        comboBox.setSelectedItem(null);
        panel.add(comboBox);
        frame.add(panel);
        frame.setSize(200, 100);
        frame.setVisible(true);
    }

    public static void main(String[] args) throws ClassNotFoundException, InstantiationException, IllegalAccessException,
            UnsupportedLookAndFeelException {
        SwingUtilities.invokeLater(new Runnable() {

            @Override
            public void run() {
                new TestComboBox().initUI();
            }
        });
    }
}

编辑2：与@Enwired讨论后，出现了另一种解决方案，即直接覆盖ListCellRenderer getPreferredSize。在这一个你可以尝试通过不同的可用L＆amp; F。

import java.awt.Component;
import java.awt.Dimension;
import java.awt.GridBagLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.DefaultListCellRenderer;
import javax.swing.JComboBox;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JList;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import javax.swing.UIManager;
import javax.swing.UIManager.LookAndFeelInfo;
import javax.swing.UnsupportedLookAndFeelException;

public class TestComboBox {

    protected void initUI() {
        final JFrame frame = new JFrame(TestComboBox.class.getSimpleName());
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        JPanel panel = new JPanel(new GridBagLayout());
        JComboBox comboBox = new JComboBox(new Object[] { "Something", "Stuff", "Beep" });
        comboBox.setRenderer(new DefaultListCellRenderer() {

            private Dimension nullDimesion;

            @Override
            public Component getListCellRendererComponent(JList list, Object value, int index, boolean isSelected, boolean cellHasFocus) {
                if (value != null && nullDimesion == null) {
                    nullDimesion = ((JComponent) getListCellRendererComponent(list, null, -1, false, false)).getPreferredSize();
                }
                Component comp = super.getListCellRendererComponent(list, value, index, isSelected, cellHasFocus);
                if (value == null) {
                    setText("No selection");
                }
                return comp;
            }

            @Override
            public Dimension getPreferredSize() {
                Dimension preferredSize = super.getPreferredSize();
                if (nullDimesion != null) {
                    preferredSize.width = Math.max(preferredSize.width, nullDimesion.width);
                    preferredSize.height = Math.max(preferredSize.height, nullDimesion.height);
                }
                return preferredSize;
            }

            @Override
            public void updateUI() {
                nullDimesion = null;
                super.updateUI();
            }
        });
        comboBox.setSelectedItem(null);
        final JComboBox uiComboBox = new JComboBox(UIManager.getInstalledLookAndFeels());
        uiComboBox.setRenderer(new DefaultListCellRenderer() {
            @Override
            public Component getListCellRendererComponent(JList list, Object value, int index, boolean isSelected, boolean cellHasFocus) {
                Component comp = super.getListCellRendererComponent(list, value, index, isSelected, cellHasFocus);
                if (value instanceof LookAndFeelInfo) {
                    LookAndFeelInfo info = (LookAndFeelInfo) value;
                    setText(info.getName());
                }
                return comp;
            }
        });
        uiComboBox.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {
                SwingUtilities.invokeLater(new Runnable() {
                    @Override
                    public void run() {
                        try {
                            UIManager.setLookAndFeel(((LookAndFeelInfo) uiComboBox.getSelectedItem()).getClassName());
                            SwingUtilities.updateComponentTreeUI(frame);
                        } catch (ClassNotFoundException e1) {
                            // TODO Auto-generated catch block
                            e1.printStackTrace();
                        } catch (InstantiationException e1) {
                            // TODO Auto-generated catch block
                            e1.printStackTrace();
                        } catch (IllegalAccessException e1) {
                            // TODO Auto-generated catch block
                            e1.printStackTrace();
                        } catch (UnsupportedLookAndFeelException e1) {
                            // TODO Auto-generated catch block
                            e1.printStackTrace();
                        }
                    }
                });
            }
        });
        panel.add(comboBox);
        panel.add(uiComboBox);
        frame.add(panel);
        frame.setSize(300, 100);
        frame.setVisible(true);
    }

    public static void main(String[] args) throws ClassNotFoundException, InstantiationException, IllegalAccessException,
            UnsupportedLookAndFeelException {
        SwingUtilities.invokeLater(new Runnable() {

            @Override
            public void run() {
                new TestComboBox().initUI();
            }
        });
    }
}

JComboBox首选大小，选择空值但不在ComboBoxModel中

3 个答案: