我正在尝试使用gui，这取决于用户从第一个列表中选择的内容，然后第二个列表变为可见。
为了做到这一点，我需要在第一个组合框中添加一个动作监听器。然后在动作侦听器类中执行switch语句。但是，当我实现它时，我遇到了错误。
您是否可以在占位符空组合框上附加完整的组合框？
package balanceThatSheep;
/*
* This Class is the GUI for the program.
*/
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class BalancingInterface extends JFrame{
private JLabel sexL, classL, weightL, forageL, concentratesL;
private JButton calculateB, exitB;
private CalculateButtonHandler cbHandler;
private ExitButtonHandler ebHandler;
private SheepTypeListHandler stlHandler;
private static final int WIDTH = 600;
private static final int HEIGHT = 500;
public BalancingInterface(Data getSomeData){
// Create four labels
sexL = new JLabel("Select Sheep Type: ", SwingConstants.CENTER);
classL = new JLabel("Select Sheep Classification: ", SwingConstants.CENTER);
weightL = new JLabel("Select Sheep Weight: ", SwingConstants.CENTER);
forageL = new JLabel("Select a Forage: ", SwingConstants.CENTER);
concentratesL = new JLabel("Select Feed Concentrates: ", SwingConstants.CENTER);
//Create the Arrays
String [] sheepType = {"Ewe", "Ram", "Lamb"}; //Three Choices - can only pick one
String [] eweClass = {"Maintenance", "Nonlactating, first 15 weeks gestation",
"Last 6 wks gestation OR Last 8 wks lactation suckling singles",
"First 8 wks lactation suckling singles OR last 8 wks lactation suckling twins",
"First 8 weeks lactation suckling twins", "Replacement lambs and yearlings"};
String [] ramClass = {"Replacement lambs and yearlings"}; //This is the only option for Rams
String [] lambClass = {"Finishing", "Early-weaned"}; //Only 2 choices
String [] forageNames = getSomeData.getForageNames(); //Pull in the forage names
String [] placeholder = {""}; //Use this list as a placeholder
//Create Drop Down Lists
JComboBox<String> sheepListCB = new JComboBox<>(sheepType); //Can Only Pick one element - good
JComboBox<String> sheepEweClassCB = new JComboBox<>(eweClass); //If ewe selected
JComboBox<String> sheepRamClassCB = new JComboBox<>(ramClass); //If ram selected
JComboBox<String> sheepLambClassCB = new JComboBox<>(lambClass); //If lamb selected
JComboBox<String> foragesCB = new JComboBox<>(forageNames); //Can Only Pick one element - good
JComboBox<String> placeholderCB = new JComboBox<>(placeholder); //Use as a placeholder
JComboBox<String> placeholder2CB = new JComboBox<>(placeholder); //Use as a placeholder
JComboBox<String> placeholder3CB = new JComboBox<>(placeholder); //Use as a placeholder
//Create Calculate Button
calculateB = new JButton("Calculate");
cbHandler = new CalculateButtonHandler();
calculateB.addActionListener(cbHandler);
//Calculate button you are making the program listen to it.
//Create Exit Button
exitB = new JButton("Exit");
ebHandler = new ExitButtonHandler();
exitB.addActionListener(ebHandler);
//Handle the Selection of the Sheep Type
stlHandler = new SheepTypeListHandler();
sheepListCB.addActionListener(stlHandler);
//Set the title of the window box
setTitle("Welcome to the Sheep Ration Balancer");
//Get the container
Container pane = getContentPane();
//Set the layout
pane.setLayout(new GridLayout(6, 2)); //6 rows, 2 columns
//Place all items created
pane.add(sexL);
pane.add(sheepListCB);
pane.add(classL);
pane.add(placeholderCB);
pane.add(weightL);
pane.add(placeholder2CB);
pane.add(forageL);
pane.add(foragesCB);
pane.add(concentratesL);
pane.add(placeholder3CB);
pane.add(calculateB);
pane.add(exitB);
//set the size of the window and display it
setSize(WIDTH,HEIGHT);
setVisible(true);
setDefaultCloseOperation(EXIT_ON_CLOSE);
//repaint - usually used for graphics - might work here
repaint();
} //End Constructor
/*
* This method will execute after the constructor
*/
public void paint(Graphics g)
{
super.paint(g);
} //End paint Method
private class SheepTypeListHandler implements ActionListener{
public void actionPerformed(ActionEvent e)
{
if (e == "ewe")
placeholderCB.append(sheepEweClassCB);
if (e == "ram")
placeholder2CB.append(sheepRamClassCB);
else
placeholder3CB.append(sheepLambClassCB);
//TODO - Finish this Method
} //End actionPerformed Method
}
private class CalculateButtonHandler implements ActionListener
{
public void actionPerformed(ActionEvent e)
{
//TODO - Finish this Method
} //End actionPerformed Method
} //End CalculateButtonHandler Class
private class ExitButtonHandler implements ActionListener
{
public void actionPerformed(ActionEvent e)
{
System.exit(0);
} //End actionPerformed Method
} //End ExitButton Method Class
} //End of BalancingInterface Class
完整的代码如上所示。我正在使用的组合框是“sheepListCB”，上面的动作监听器显示了我的逻辑，用于实现下一个显示的组合框。但是，它不起作用。
答案 0 :(得分：2)
也许你想要这样的东西。
从第一个组合框中选择一个值，然后填充第二个组合框：
import java.awt.*;
import java.awt.event.*;
import java.util.*;
import javax.swing.*;
public class ComboBoxTwo extends JPanel implements ActionListener
{
private JComboBox<String> mainComboBox;
private JComboBox<String> subComboBox;
private Hashtable<String, String[]> subItems = new Hashtable<String, String[]>();
public ComboBoxTwo()
{
String[] items = { "Select Item", "Color", "Shape", "Fruit" };
mainComboBox = new JComboBox<String>( items );
mainComboBox.addActionListener( this );
// prevent action events from being fired when the up/down arrow keys are used
mainComboBox.putClientProperty("JComboBox.isTableCellEditor", Boolean.TRUE);
add( mainComboBox );
// Create sub combo box with multiple models
subComboBox = new JComboBox<String>();
subComboBox.setPrototypeDisplayValue("XXXXXXXXXX"); // JDK1.4
add( subComboBox );
String[] subItems1 = { "Select Color", "Red", "Blue", "Green" };
subItems.put(items[1], subItems1);
String[] subItems2 = { "Select Shape", "Circle", "Square", "Triangle" };
subItems.put(items[2], subItems2);
String[] subItems3 = { "Select Fruit", "Apple", "Orange", "Banana" };
subItems.put(items[3], subItems3);
}
public void actionPerformed(ActionEvent e)
{
String item = (String)mainComboBox.getSelectedItem();
Object o = subItems.get( item );
if (o == null)
{
subComboBox.setModel( new DefaultComboBoxModel() );
}
else
{
subComboBox.setModel( new DefaultComboBoxModel( (String[])o ) );
}
}
private static void createAndShowUI()
{
JFrame frame = new JFrame("SSCCE");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add( new ComboBoxTwo() );
frame.setLocationByPlatform( true );
frame.pack();
frame.setVisible( true );
}
public static void main(String[] args)
{
EventQueue.invokeLater(new Runnable()
{
public void run()
{
createAndShowUI();
}
});
}
}