Question

我有一个java程序，它将根据用户输入创建一个JComboBoxes数组。如果用户输入为1，则显示comboBox。如果输入大于1，我似乎得到一个普通的JFrame。

import javax.swing.*;
import java.awt.*;

class test
{
    public static void main (String Args [])
    {
    JFrame processDetail = new JFrame("Enter information for processes");
    JPanel panelDetail = new JPanel(new FlowLayout());
    String [] Processes = {"1","2","3","4","5","6","7","8","9","10"};
    processDetail.setSize(500,500);
    processDetail.setVisible(true);

        JComboBox [] AT = new JComboBox[4];  //initailse drop down, numProcc is user integer...
        for (int i = 0; i < 4; i++){
            AT[i] = new JComboBox(Processes); //processes is array of numbers
            System.out.println(i); //a check to see it was looping
            panelDetail.add(AT[i]);
        }
        //add the panel to the frame
        processDetail.add(panelDetail);
        }
    }

为什么我似乎没有得到所需数量的组合框？

Answer 1

您刚刚发现了在AWT事件调度线程中执行Swing操作失败的一个陷阱。

Swing is single-threaded.几乎所有Swing方法都必须才能在事件调度线程中执行。

如果他们不是，他们可能似乎工作，但你会得到不可预知的行为，就像你现在看到的那样。

如果将所有代码移动到Runnable并将Runnable传递给EventQueue.invokeLater（或SwingUtilities.invokeLater，这是EventQueue.invokeLater的同义词），您的问题就会消失。

Answer 2

如果您在processDetail.setVisible(true);之后放置processDetail.add(panelDetail);，它应该可以正常工作。

JFrame processDetail = new JFrame("Enter information for processes");
JPanel panelDetail = new JPanel(new FlowLayout());
processDetail.setSize(500, 500);
//processDetail.setVisible(true); Not here,
String[] processes = {"1" , "2", "3", "4"};

JComboBox[] AT = new JComboBox[4];  //initailse drop down, numProcc is user integer...
for (int i = 0; i < 4; i++) {
    AT[i] = new JComboBox(processes); //processes is array of numbers
    System.out.println(i); //a check to see it was looping
    panelDetail.add(AT[i]);
}
//add the panel to the frame
processDetail.add(panelDetail);
processDetail.setVisible(true); // <--- but here.

因为如果你将它设置为可见然后添加一些组件，它们就不会显示，因为没有任何东西告诉它将它们设置为可见。

Java JComboBox数组只显示一个元素

2 个答案: