如何在ComboBox上使用ActionListener为变量赋值 [英] How to use ActionListener on a ComboBox to give a variable a value
问题描述
我正在使用BlueJ，但遇到了问题。我有一个带有3个选项的组合框。每个选项都是一个字符串。这三个选项是日，周和月。我想做的是，如果选择的Day大于等于30（双精度）的变量，依此类推。有人可以帮我买吗，告诉我如何根据组合框中的所选选项为 emailvalue赋予值？
Im using BlueJ and I have run into problem. I have a combo box with 3 options. Each option is a string. The three options are Day, Week, and Month. What I want to do is if Day is picked than a variable equals 30 (a double) and so on. Can someone help me buy telling me how to give "emailvalue" a value based on the selected option in the combobox?
编辑：我将添加我的实际程序代码，该程序代码是每月的数据计算工具。确实会编译。
Im going to add my actual program code which is a monthly data calculater. It does compile.
这里是代码：
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.event.*;
import java.awt.image.*;
import java.awt.geom.*;
import java.awt.Color;
import java.awt.Container;
import java.awt.Graphics;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
/**
* @author (Andrew Napier, Sikander Singh)
* @version (December 18th, 2012)
*/
public class MonthlyData extends JFrame
{
private JLabel title, stitle, l1,l2,l3,l4,l5,l6,l7,l8,l9,l10,l11,l12,l13,l14;
private JLabel l15,l16,l17,l18,l19,l20,l21,l22,l23,l24,l25,l26,l27,l28,l29;
private JLabel Usage,Estimated,solu1,solu2,total2;
private JPanel panel1, panel2, panel3, panel4, panel5, panel6, panel7;
String[] deviceStrings = { "Blackberry", "Other", "Internetstick"};
String[] date = { "Day", "Week", "Month"};
public double email2 = 0;
public double email1;
static final int email50 = 50;
static final int email100 = 100;
static final int email150 = 150;
static final int email200 = 200;
static final int email250 = 250;
static final int email300 = 300;
public JSlider Email = new JSlider(0,300,0);
public JSlider Web = new JSlider(0,500,0);
public JSlider IM = new JSlider(0,500,0);
public JSlider Video = new JSlider(0,300,0);
public JSlider Song = new JSlider(0,200,0);
public JSlider App_G = new JSlider(0,100,0);
public String currentdate;
public double emailvalue;
public MonthlyData ()
{
super ("MonthlyData");
setSize (1000,1100);
////////////////////////////////////////////////////// panel1
panel1 = new JPanel ();
panel1.setLayout (new GridLayout(1,1));
panel1.setVisible(true);
panel1.setBackground (Color.black);
title = new JLabel (" WANNA KNOW HOW MUCH DATA",JLabel.LEFT);
title.setForeground(Color.white);
title.setFont (new Font("Times New Roman",Font.BOLD,25));
l1 = new JLabel ("");
l2 = new JLabel ("");
/////////////////////////////////////////////// panel2
panel2 = new JPanel ();
panel2.setLayout (new GridLayout(1,1));
panel2.setVisible(true);
panel2.setBackground (Color.gray);
stitle = new JLabel (" PICK A PHONE OR INTERNET STICK AND THEN DRAG THE .",JLabel.LEFT);
stitle.setForeground(Color.black);
stitle.setFont (new Font("Times New Roman",Font.BOLD,14));
//////////////////////////////////////////////// panel3
panel3 = new JPanel ();
panel3.setLayout (new FlowLayout());
panel3.setVisible(true);
panel3.setBackground (Color.white);
l3 = new JLabel ("Select Your Device:",JLabel.RIGHT);
l3.setForeground(Color.red);
JComboBox devicelist = new JComboBox (deviceStrings);
l4 = new JLabel ("Tell us how much of what's listed here you think you'll use:");
///////////////////////////////////////////////// panel4
panel4 = new JPanel ();
panel4.setLayout (new GridLayout(6,7));
panel4.setVisible(true);
panel4.setBackground (Color.white);
l5 = new JLabel ("Email");
l6 = new JLabel ("WebPage");
l7 = new JLabel ("Instant Message");
l8 = new JLabel ("Streaming Video");
l9 = new JLabel ("Song");
l10 = new JLabel ("Application or Game");
l11 = new JLabel (""+" Emails");
final JComboBox date1 = new JComboBox (date);
date1.addActionListener(new ActionListener() {//add actionlistner to listen for change
@Override
public void actionPerformed(ActionEvent e) {
String s = (String) date1.getSelectedItem();//get the selected item
switch (s) {//check for a match
case "Day":
emailvalue = 30;
break;
case "Week":
emailvalue = 4;
break;
case "Month":
emailvalue = 1;
System.out.println("Month selected, emailvalue:" + emailvalue);
break;
}
}
});
l12 = new JLabel (" 0.002 MB");
l13 = new JLabel (""+email2+" MB");
double web1 = 0;
l14 = new JLabel (""+web1+" WebPages");
JComboBox date2 = new JComboBox (date);
l15 = new JLabel (" 0.07 MB");
double web2 = 0;
l16 = new JLabel (""+web2+" MB");
double IM1 = 0;
l17 = new JLabel (""+IM1+" IMs");
JComboBox date3 = new JComboBox (date);
l18 = new JLabel (" 0.005 MB");
double IM2 = 0;
l19 = new JLabel (""+IM2+" MB");
double video1 = 0;
l20 = new JLabel (""+video1+" Minutes");
JComboBox date4 = new JComboBox (date);
l21 = new JLabel (" 1 MB");
double video2 = 0;
l22 = new JLabel (""+video2+" MB");
double song1 = 0;
l23 = new JLabel (""+song1+" MP3's");
JComboBox date5 = new JComboBox (date);
l24 = new JLabel (" 4 MB");
double song2 = 0;
l25 = new JLabel (""+song2+" MB");
double app1 = 0;
l26 = new JLabel (""+app1+" App/Games");
JComboBox date6 = new JComboBox (date);
l27 = new JLabel (" 0.44 MB");
double app2 = 0;
l28 = new JLabel (""+app2+" MB");
//////////////////////////////////////////////// panel5
panel5 = new JPanel ();
panel5.setLayout (new GridLayout(1,1));
panel5.setVisible(true);
panel5.setBackground (Color.white);
solu1 = new JLabel ("WE THINK YOUR MONTHLY DATA USAGE WILL BE:");
solu1.setForeground (Color.red);
solu1.setFont (new Font("Times New Roman",Font.BOLD,20));
double total = 0;
total2 = new JLabel (""+total+" MB");
total2.setForeground (Color.red);
total2.setFont (new Font("Times New Roman",Font.BOLD,20));
/////////////////////////////////////////// panel6
panel6 = new JPanel ();
panel6.setLayout (new GridLayout (1,1));
panel6.setVisible (true);
panel6.setBackground (Color.white);
Usage = new JLabel ("Usage per unit");
Usage.setForeground (Color.red);
Estimated = new JLabel (" Estimated total");
Estimated.setForeground (Color.red);
////////////////////////////////////////////// panel7
panel7 = new JPanel ();
panel7.setLayout (new GridLayout (1,1));
panel7.setVisible (true);
panel7.setBackground (Color.white);
solu2 = new JLabel ("Data usage varies by device and other factors and the .");
solu2.setForeground (Color.black);
/////////////////////////////////////////////////// Implements
Container container = getContentPane ();
container.setLayout (null); //changed
container.setBackground (Color.white);
container.add (panel1).setBounds (0,0,1000,120); //panel1
panel1.add (title).setSize(500,500);
container.add (panel2).setBounds (0,100,1000,120); //panel2
panel2.add (stitle);
container.add (panel3).setBounds (0,220,1000,100); //panel3
panel3.add (l3);
panel3.add (devicelist);
panel3.add (l4);
container.add (panel4).setBounds (0,340,1000,150); //panel4
Email.addChangeListener(new SliderHandler());
Web.addChangeListener(new SliderHandler());
IM.addChangeListener(new SliderHandler());
Video.addChangeListener(new SliderHandler());
Song.addChangeListener(new SliderHandler());
App_G.addChangeListener(new SliderHandler());
panel4.add (l5);
panel4.add (Email);
panel4.add (l11);
panel4.add (date1);
panel4.add (l12);
panel4.add (l13);
panel4.add (l6);
panel4.add (Web);
panel4.add (l14);
panel4.add (date2);
panel4.add (l15);
panel4.add (l16);
panel4.add (l7);
panel4.add (IM);
panel4.add (l17);
panel4.add (date3);
panel4.add (l18);
panel4.add (l19);
panel4.add (l8);
panel4.add (Video);
panel4.add (l20);
panel4.add (date4);
panel4.add (l21);
panel4.add (l22);
panel4.add (l9);
panel4.add (Song);
panel4.add (l23);
panel4.add (date5);
panel4.add (l24);
panel4.add (l25);
panel4.add (l10);
panel4.add (App_G);
panel4.add (l26);
panel4.add (date6);
panel4.add (l27);
panel4.add (l28);
container.add (panel5).setBounds (210,540,1000,50); // panel5
panel5.add (solu1);
panel5.add (total2);
container.add (panel6).setBounds (670,220,200,220); // panel6
panel6.add (Usage);
panel6.add (Estimated);
container.add (panel7).setBounds (210,580,530,50); // panel7
panel7.add (solu2);
Email.setOpaque(false);
Web.setOpaque(false);
IM.setOpaque(false);
Video.setOpaque(false);
Song.setOpaque(false);
App_G.setOpaque(false);
setVisible (true);
}
public static void main (String[] args)
{
MonthlyData application = new MonthlyData ();
}
public class SliderHandler implements ChangeListener
{
public void stateChanged(ChangeEvent e)
{
if (e.getSource().equals(Email))
{
l11.setText(""+Email.getValue());
email2= (Email.getValue() * 0.002);
l13.setText(email2 + "MB");
}
if (e.getSource().equals(Web))
{
l14.setText(""+Web.getValue());
}
if (e.getSource().equals(IM))
{
l17.setText(""+IM.getValue());
}
if (e.getSource().equals(Video))
{
l20.setText(""+Video.getValue());
}
if (e.getSource().equals(Song))
{
l23.setText(""+Song.getValue());
}
if (e.getSource().equals(App_G))
{
l26.setText(""+App_G.getValue());
}
}
}
public void paint (Graphics g)
{
super.paint(g);
}
}
推荐答案
1 ）首先，您需要在 JComboBox 中添加 ActionListener 来侦听选定项的更改。
1) Well firstly you'd need an ActionListener added to the JComboBox to listen for selected item changes.
2）在 ActionListener 的 actionPerformed（...）中通过 getSelectedItem（）选择项目并转换为 String ，因为该方法返回 Object 。
2) Within actionPerformed(...) of ActionListener get the selected item via getSelectedItem() and cast to a String as the method returns an Object.
3）使用 switch 语句检查所选项目与哪个项目匹配，即
3) Use a switch statement to check which one the selected item matches i.e day, month,week and than assign a value accordingly.
例如：
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.SwingUtilities;
public class MonthlyData {
public double emailvalue;
private String[] date = {"Day", "Week", "Month"};
private JFrame frame;
public MonthlyData() {
frame = new JFrame();//use an instance rather than extending the class
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
final JComboBox date1 = new JComboBox(date);
ActionListener cbActionListener = new ActionListener() {//add actionlistner to listen for change
@Override
public void actionPerformed(ActionEvent e) {
String s = (String) date1.getSelectedItem();//get the selected item
switch (s) {//check for a match
case "Day":
emailvalue = 1.1;
System.out.println("Day selected, emailvalue:" + emailvalue);
break;
case "Week":
emailvalue = 2.2;
System.out.println("Week selected, emailvalue:" + emailvalue);
break;
case "Month":
emailvalue = 3.3;
System.out.println("Month selected, emailvalue:" + emailvalue);
break;
default:
emailvalue = 4.4;
System.out.println("No match selected, emailvalue:" + emailvalue);
break;
}
}
};
date1.addActionListener(cbActionListener);
frame.add(date1);
frame.pack();
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
@Override
public void run() {
new MonthlyData();
}
});
}
}
更新：
添加SSCCE并评论后：
After you added an SSCCE and commented:
如果您转到SliderHandler类别，输入
email2 =（Email.getValue（）* 0.002）* emailvalue;如果您这样做，标签将不会实时更新
。但是如果您用5来代替emailvalue，那么
将会更新
If you go down to the SliderHandler class, type in email2=(Email.getValue() * 0.002)*emailvalue; if you do the label wont update in real time. but if you replace emailvalue with lets say 5, it will update
问题是
启动时尚未设置电子邮件值。仅在第一次更改所选项目/索引时设置。
On start up the emailvalue is not yet set. It will only be set on the first time the selected item/index is changed.
要解决此问题，我们只需调用<$ c $即可为其提供默认选择值c> setSelectedItem（..）在可见之前
To solve this we must simply give it a default selected value by calling setSelectedItem(..) before its visible:
final JComboBox date1 = new JComboBox(date);
date1.addActionListener(new ActionListener() {//add actionlistner to listen for change
@Override
public void actionPerformed(ActionEvent e) {
String s = (String) date1.getSelectedItem();//get the selected item
switch (s) {//check for a match
case "Day":
emailvalue = 30;
break;
case "Week":
emailvalue = 4;
break;
case "Month":
emailvalue = 1;
System.out.println("Month selected, emailvalue:" + emailvalue);
break;
}
}
});
date1.setSelectedItem(date[0]);//set Day as default selected item/emailvalue
关于代码的建议：
-
应在上创建并处理Swing组件href = http://docs.oracle.com/javase/tutorial/uiswing/concurrency/dispatch.html rel = nofollow>
EDT通过SwingUtilities.invokeLater（Runnable r）块。
不要覆盖 paint（ ..）的 JFrame 而不是添加 JPanel 并覆盖 paintComponent （图形g）
Dont override paint(..) of JFrame rather add JPanel and override paintComponent(Graphics g)
不要调用 setBounds 或 setSize 而不是使用适当的 LayoutManager 和/或覆盖 getPreferredSize（） code> JPanel 并返回适合其内容的 Dimension s，而不是调用 pack（） JFrame 上将c>设置为可见。
Dont call setBounds or setSize rather use an appropriate LayoutManager and/or override getPreferredSize() of JPanel and return Dimensions which fit its contents than call pack() on JFrame before setting it visible.
不要扩展 JFrame 不必要
不要在类上实现 ActionListener ，除非该类将用作一个类，或者必须公开其方法到其他班级
Dont implement ActionListener on the class unless the class will be used as one and or its methods must be exposed to other classes
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