从其他类获取Jcomponent更改帧大小 [英] getting Jcomponent from other class changes frame size

问题描述

您好我尝试从其他类获取jcomponent。组件正在显示，但我的帧大小发生了变化。

Hello I am try to get jcomponent from other class.the components are displaying but my frame size changes.

Example.java

public class Example extends JFrame{

  static JPanel panel = new JPanel();
  static A a = new A();
  static B b = new B();
  static JComboBox<String> combo = new JComboBox<>();   
  static String value;

     Example(){
        setSize(400, 400);
        combo.setBounds(450, 140, 50, 20);
        combo.addItem("");
        combo.addItem("a");
        combo.addItem("b");
        combo.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {
                value = (String) combo.getSelectedItem().toString();
                if(value.equals("a")){
                    panel.add(a.getLabel());
                    panel.remove(b.getLabel());
                    add(panel);
                    pack(); 
                }else if(value.equals("b")){
                    panel.add(b.getLabel());
                    panel.remove(a.getLabel());
                    add(panel);
                    pack();
                }
            }
        });
        panel.add(combo);
        this.add(panel);
        setVisible(true);
        }
}

A.java

public class A extends JFrame{

  JPanel panel = new JPanel();
  JLabel lab = new JLabel("Text");

  A(){
      lab.setBounds(280, 25, 150, 50);
      lab.setVisible(true);
      panel.add(lab);
      add(panel);
  }
  public  JLabel getLabel(){
    return lab;
  }
}

B.java

public class B extends JFrame{

    JPanel panel = new JPanel();
    JButton lab = new JButton("Hello");

    B(){
       lab.setBounds(380, 25, 250, 50);
       lab.setVisible(true);
       panel.add(lab);
       add(panel);
    }
    public JButton getLabel(){
       return lab;  
    }
}

Main.java

public class Main {
  public static void main(String [] agrs) {
    Example ex = new Example();
    ex.setVisible(true);
  }
}

当我按照定义的大小运行帧打开但是当我从组合框中选择 a ，帧大小减少任何建议，以便屏幕大小保持不变。

when I run frame open as defined size but when I select a from combo box the frame size decreases any suggestion so as screen size remain same.

推荐答案

解决这个问题的快速而肮脏的方法是摆脱 pack（）和替代 revalidate（）和重绘：

The quick and dirty way to solve this is to get rid of pack() and subsitute revalidate() and repaint:

add(panel);
revalidate();
repaint();
// pack();

• revalidate 告诉布局管理员重新布局他们的组件。


• 重绘请求重新绘制组件，尤其是脏区域


• pack 告诉窗口重新布局所有组件并调整大小到最佳尺寸。


• revalidate tells the layout managers to re-lay out their components.
• repaint requests that the component be repainted, especially "dirty" regions
• pack tells the window to re-lay out all components and resize to the optimal size.

使用CardLayout要好得多，窗口和组件大小将保持不变，大到足以容纳最大的组件。 ...并避免使用空布局。

Much better would be to use a CardLayout, and the window and component size will remain constant, big enough to fit the largest component. ... and avoid all use of null layouts.

例如：

import java.awt.CardLayout;
import java.awt.Dimension;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.*;

public class Example2 extends JPanel {
   public static final String[] COMBO_TEXTS = {"", "a", "b"};
   private static final int PREF_W = 400;
   private static final int PREF_H = PREF_W;
   private DefaultComboBoxModel<String > comboModel = new DefaultComboBoxModel<>(COMBO_TEXTS);
   private CardLayout cardLayout = new CardLayout();

   public Example2() {
      setLayout(cardLayout);
      ComboListener comboListener = new ComboListener();

      JComboBox<String> combo = new JComboBox<>(comboModel);
      combo.addActionListener(comboListener);;
      JPanel panelBlank = new JPanel();
      panelBlank.add(combo);

      JPanel panelWithText = new JPanel();
      combo = new JComboBox<>(comboModel);
      combo.addActionListener(comboListener);;
      panelWithText = new JPanel();
      panelWithText.add(combo);
      panelWithText.add(new JLabel("Text"));

      JPanel panelWithButton = new JPanel();
      combo = new JComboBox<>(comboModel);
      combo.addActionListener(comboListener);;
      panelWithButton = new JPanel();
      panelWithButton.add(combo);
      panelWithButton.add(new JButton("Hello"));

      add(panelBlank, COMBO_TEXTS[0]);
      add(panelWithText, COMBO_TEXTS[1]);
      add(panelWithButton, COMBO_TEXTS[2]);
   }

   @Override
   public Dimension getPreferredSize() {
      return new Dimension(PREF_W, PREF_H);
   }

   private class ComboListener implements ActionListener {
      @Override
      public void actionPerformed(ActionEvent e) {
         JComboBox<String> combo = (JComboBox<String>)e.getSource();
         String item = combo.getSelectedItem().toString();
         cardLayout.show(Example2.this, item);
      }
   }

   private static void createAndShowGui() {
      Example2 mainPanel = new Example2();

      JFrame frame = new JFrame("Example2");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.getContentPane().add(mainPanel);
      frame.pack();
      frame.setLocationByPlatform(true);
      frame.setVisible(true);
   }

   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            createAndShowGui();
         }
      });
   }
}

这样可以简化事情并使自己更难拍摄脚。所以不是这样：

This simplifies things and makes it harder to shoot yourself in the foot. So rather than this:

        public void actionPerformed(ActionEvent e) {
            value = (String) combo.getSelectedItem().toString();
            if(value.equals("a")){
                panel.add(a.getLabel());
                panel.remove(b.getLabel());
                // add(panel);
                // pack();
            }else if(value.equals("b")){
                panel.add(b.getLabel());
                panel.remove(a.getLabel());
                // add(panel);
                // pack();
            }
            add(panel);
            revalidate();
            repaint();
        }

你的ActionListener的actionPerformed方法就是这样：

Your ActionListener's actionPerformed method is just this:

  public void actionPerformed(ActionEvent e) {
     JComboBox<String> combo = (JComboBox<String>)e.getSource();
     String item = combo.getSelectedItem().toString();
     cardLayout.show(Example2.this, item);
  }





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有关CardLayout的更多信息，其用途和功能，请查看 CardLayout教程。但简而言之，它可以自动化在GUI中交换视图的过程，从而使自己更难以在脚下拍摄。

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For more on the CardLayout, its uses and functionality, please check out the CardLayout Tutorial. But in a nutshell, it automates the process of swapping "views" in a GUI, making it much harder to shoot yourself in the foot.

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