JComboBox首選大小與空值選擇，但不是在ComboBoxModel

Question

我有以下情況：在JCombobox中，首選大小是基於最大的項目大小。但是，此計算不考慮爲null提供的值。它只關心模型中的值。所以當渲染空值的文本大於其他元素時，標籤被截斷，並且在末尾有三個點（...）。我想避免這種情況。

這裏是我談論的一個小的演示：

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(); 
      } 
     }); 
    } 
} 

如果您有任何建議，我想知道。到目前爲止，我的想法是擴展JComboBox，重寫首選大小，同時執行null值的呈現，並將調用的最大維度取爲super.preferredSize和空值呈現之一。但我覺得這有點令人失望。

我真的不喜歡使用prototypeDisplayValue 絕對不是一個選項，因爲我不知道將在該下拉列表中的值 。

Answer 1

我沒有代碼測試這一點，但我的辦法是：

1. 確定的preferredSize之間的差異渲染器返回的Component以及JComboBox的實際preferredSize。不是通過使用任何硬編碼的值，而是通過創建僅包含一個項目和已知渲染器的幕後的JComboBox，並將JComboBox的首選大小與由已知渲染器返回的Component的大小進行比較。每個外觀和手感由收聽者附接到UIManager
2. 覆蓋實際JComboBox的getPreferredSize和返回的最大的super.getPreferredSize()寬度和getPreferredSize(rendererComponent) + calculatedDifference

改變時間

重複步驟1

這應該注意外觀問題，避免不必要的計算，並且您可以輕鬆創建包含此功能的JComboBox擴展。

Answer 2

我要採取的事實，我們知道，從Component返回DefaultListCellRenderer.getListCellRendererComponent優點是DefaultListCellRenderer對象本身，而在於它是JLabel一個實例。

我還假設您的外觀和感覺以通常的方式計算組合框的首選大小，類似於BasicComboBoxUI。

有了這些信息，這種解決方案也許是醜陋和低效，但它的工作原理：

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; 
     } 
     } 

Answer 3

所以這是我這麼遠，但一個主要問題是跨大號&˚F問題。另一種方法是遍歷ComboBox模型的所有值和「無選擇」值，並檢查哪一個是最長的。然後我可以將它設置爲prototypeDisplayValue。問題是我需要一個圖形上下文來衡量每個字符串的邊界。

以下是我們用@Enwired和@Robin發現的兩種解決方案。感謝他們兩人。

編輯：在與@羅賓討論後，我發現這個解決方案實際上更簡單，適用於所有平臺和外觀。唯一的缺點是我們需要創建一個額外的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(); 
      } 
     }); 
    } 
} 

編輯2：與@Enwired討論在此之後的替代解決方案提出了這是直接重寫ListCellRenderer的getPreferredSize。在這其中，你可以嘗試去通過不同得的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(); 
      } 
     }); 
    } 
}