5

我有以下情况：在 JCombobox 中，首选大小基于最大项目大小。但是，此计算没有考虑为 呈现的值null。它只关心模型内部的值。因此，当用于呈现空值的文本大于其他元素时，标签会被截断，最后会出现三个点 (...)。我想避免这种情况。

这是我正在谈论的内容的一个小演示：

呈现截断的空值

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();
            }
        });
    }
}

我想知道你有没有什么建议。到目前为止，我的想法是扩展 JComboBox，覆盖首选大小，还执行空值渲染，并采用调用 super.preferredSize 的最大维度和空值渲染之一。但我觉得这有点令人失望。

我真的不希望使用prototypeDisplayValue绝对不是一个选项，因为我不知道该下拉菜单中的值。

4

3 回答 3

2

我没有在代码中对此进行测试，但我的方法是：

  1. 确定渲染器返回的与实际preferredSize的. 不是通过使用任何硬编码值，而是通过创建一个仅包含一个项目和一个已知渲染器的幕后，并将首选大小与已知渲染器返回的大小进行比较。ComponentpreferredSizeJComboBoxJComboBoxJComboBoxComponent
  2. 每次通过将侦听器附加到UIManager
  3. 覆盖getPreferredSize实际的JComboBox并返回宽度的最大值super.getPreferredSize()和getPreferredSize( rendererComponent ) + calculatedDifference

这应该解决外观问题，避免不必要的计算，并且您可以轻松创建JComboBox包含此功能的扩展。

于 2012-07-20T19:00:57.073 回答
1

我将利用这样一个事实，即我们知道Component返回的 fromDefaultListCellRenderer.getListCellRendererComponent是DefaultListCellRenderer对象本身，并且它是JLabel.

我还假设您的外观以通常的方式计算组合框首选大小，类似于BasicComboBoxUI.

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：

    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;
        }

      @Override
      public Dimension getPreferredSize() {
        // this doesn't work:
        // int minWidth = (new JLabel("No selection").getPreferredSize()).width;

        // this does work:
        String oldText = getText();
        setText("No selection");
        int minWidth = (super.getPreferredSize()).width;
        setText(oldText);


        Dimension d = super.getPreferredSize();
        if (d.width < minWidth) {
          return new Dimension(minWidth, d.height);
        } else {
          return d;
        }
      }
于 2012-07-20T17:29:38.953 回答
0

到目前为止，这就是我所得到的，但一个主要问题是交叉 L&F 问题。另一种方法是遍历 ComboBox 模型的所有值和“无选择”值，并检查哪个是最长的。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。

以下是我们使用@Enwired 和@Robin 找到的两个解决方案。感谢他们俩。

编辑：在与@Robin 讨论后，我发现这个解决方案实际上要简单得多，并且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：在与@Enwired 讨论后，提出了这个替代解决方案，即直接覆盖ListCellRenderer getPreferredSize。在这一个中，您可以尝试浏览不同的可用 L&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();
            }
        });
    }
}
于 2012-07-20T18:45:58.247 回答