高分诚心请教:用多个jcombobox的选项组成sql语句的查询，如何传递点击选项后的参数？不点击可以用getselecteditem,点击选项后应该用什么

Question

RT，JAVA新手，大家帮帮忙！

Answer 1

做个SelectionListener听选项，那个选了就用getSelectedItem(),拿到然后就组装你的sql呗。

Answer 2

我代码是这样写的，但是选项改变后不能监听到，应该怎么改？public class Jcombopricename extends JPanel{ private JPanel panel;
private JLabel label;
private JComboBox jcbpr=null;
private String cboxprname;

public Jcombopricename()
{
label=new JLabel("价格");
jcbpr=new JComboBox();
jcbpr.addItem("请选择");
jcbpr.addItem("15万以下");
jcbpr.addItem("15-25万");
jcbpr.addItem("25-35万");
jcbpr.addItem("35-45万");
jcbpr.addItem("45-60万");
jcbpr.addItem("60万以上");
jcbpr.addItemListener(new ItemListener(){

public void itemStateChanged(ItemEvent e)
{
Jcombopricename.this.cboxprname=(String)jcbpr.getSelectedItem();
}
});


panel=new JPanel();
panel.add(label);
panel.add(jcbpr);
}
public JPanel getprpanel()
{
return panel;
}

public String getpricename()
{
if(cboxprname==null)
{
cboxprname=(String)jcbpr.getSelectedItem();
}
return cboxprname;
}
}

Answer 3

to obizss:jcombobox 如何监听SelectionListener？jcombobox API里好像没有这个监听，能给个例子嘛？

Answer 4

楼主，你可以为其注册一个实现了ActionListener接口的监听器，这种基本操作都可以触发主义事件：
　　jcbpr.addActionListener(new ActionListener(){public void actionPerformed(ActionEvent e)
{
Jcombopricename.this.cboxprname=(String)jcbpr.getSelectedItem();
}
});

Answer 5

我一开始就写的ActionListener 可是在public void itemStateChanged(ItemEvent e)
{
Jcombopricename.this.cboxprname=(String)jcbpr.getSelectedItem();
}
});中，cboxprname值在itemStateChanged被改变了，可是跳出itemStateChanged，cboxprname又为空了没有保存到点击的选项值，我是在无法理解。大家帮我看看应该怎么改？

Answer 6

楼主，我写了一个监听JComboBox的事件的简单实现，运行通过，是你要的效果，代码如下：
import javax.swing.*;                               
import java.awt.event.*;                            
class Test extends JFrame                           
{                                                   
  JComboBox choose;                                 
  String str;                                       
  Test()                                            
  {                                                 
   super("test");                                   
   choose=new JComboBox();                          
   choose.addItem("十万");                          
   choose.addItem("二十万");                        
   add(choose);                                     
   choose.addActionListener(new ActionListener()    
    {public void actionPerformed(ActionEvent ae)    
     {str=(String)choose.getSelectedItem();         
      System.out.println(str);                      
     }                                              
    }                                               
     );                                             
   setSize(200,300);                                
   setVisible(true);                                
  }                                             
  public static void main(String[] args)            
  {new  Test();}                             
}                                                   
楼主运行看看。

Answer 7

TO GSEAH():我想用点击下拉框中的选项，组成SQL语句的查询条件，你在 actionPerformed里可以打印出STR,也是点击的选项，但是我想把STR保存下来并提取组成SQL查询条件，我在你的基础上加入了一个public getstr(){System.out.println(str);return str;}，但是结果很意外，与在addActionListener中打印的System.out.println(str)不一样啊，结果是NULL，点击的选项没有保存下来啊有点抓狂了

Answer 8

我也是初学JAVA，想做一个MVC模式的查询体统，就这点问题搞了2－3天了，心灰意冷：（

Answer 9

public class Jcombopricename extends JPanel{private JPanel panel;
private JLabel label;
private JComboBox jcbpr=null;
private String cboxprname;public Jcombopricename()
{
label=new JLabel("价格");
jcbpr=new JComboBox();
jcbpr.addItem("请选择");
jcbpr.addItem("15万以下");
jcbpr.addItem("15-25万");
jcbpr.addItem("25-35万");
jcbpr.addItem("35-45万");
jcbpr.addItem("45-60万");
jcbpr.addItem("60万以上");
jcbpr.addItemListener(new ItemListener(){public void itemStateChanged(ItemEvent e)
{
cboxprname=(String)jcbpr.getSelectedItem();
System.out.println("after="+cboxprname);
}
});
panel=new JPanel();
panel.add(label);
panel.add(jcbpr);
}
public JPanel getprpanel()
{
return panel;
}public String getpricename()
{
if(cboxprname==null)
{
cboxprname=(String)jcbpr.getSelectedItem();
}
System.out.println("get="+cboxprname);
return cboxprname;
}
}结果:
after=别墅
get=null点击选项后的值没有保存下来：（应该改啊？

Answer 10

楼主，我在你说的基础上，加了几句，能够实现你要的效果
import javax.swing.*;                                                        
import java.awt.event.*;                                                     
class Test extends JFrame                                                    
{                                                                            
  JComboBox choose;                                                          
  String str;                                                                
  Test()                                                                     
  {                                                                          
   super("test");                                                            
   choose=new JComboBox();                                                   
   choose.addItem("十万");                                                   
   choose.addItem("二十万");                                                 
   add(choose);                                                              
   choose.addActionListener(new ActionListener()                             
    {public void actionPerformed(ActionEvent ae)                             
     {str=(String)choose.getSelectedItem();                                  
     System.out.println("aaa");                                              
     System.out.println(str);                                                
     }                                                                       
    }                                                                        
     );                                                                      
   setSize(200,300);                                                         
   setVisible(true);                                                         
  }                                                                      
                                                                             
 public void  getString()                                                    
  {  
    if(str==null)                                                            
      str=(String)choose.getSelectedItem();                                  
     System.out.println("bbb");                                              
     System.out.println(str);                                                
  }                                                                          
  public static void main(String[] args)                                     
  {Test a=new  Test();                                                       
   a.getString();                                                       
  }                                                                      
                                                                             
}                                                                            
我怀疑你的jcbpr.addItemListener(new ItemListener()）这个方法注册监听器失败，要不你在这个方法内部加上 System.out.println("aaa");  这样一句，以检测事件触发时，是否进入了监听器内部。其实你说的“TO GSEAH():”那个问题也是可以解释的，因为在getstr(){System.out.println(str);return str;}，被调用时，根本还没有触发事件，那么str当然是null了，所以，你可以你我加的那几句那样：
if(str==null)                                                            
      str=(String)choose.getSelectedItem(); 结果表明，实际上我最初发的那段代码是可以实现你要的效果的（即选定项是被保存下来了的），但是你在后面被一个现象迷惑了

Answer 11

感谢gseah()这么热心：），可以结贴了。