Question

我想放置几个按钮来检查不同布局管理器之间的差异。但是我编写的代码仅显示一个布局管理器显示的按钮，而另一个布局管理器的按钮根本不显示。我该怎么办？

这是我的代码：

import java.awt.BorderLayout;
import java.awt.FlowLayout;
import java.awt.GridLayout;

import javax.swing.*;

public class No2{
    public No2() {
        JFrame frame=new JFrame("MyFrame");
        JPanel MainPanel=new JPanel();
        JPanel panel1=new JPanel();
        JPanel panel2=new JPanel();
        JPanel panel3=new JPanel();

        JButton[] btn=new JButton[5];
        for (int i = 0; i < btn.length; i++) {
            btn[i]=new JButton("Button"+(i+1));
        }

        frame.add(MainPanel);
        MainPanel.setLayout(new GridLayout(3,1));
        MainPanel.add(panel1);
        MainPanel.add(panel2);
        MainPanel.add(panel3);

        panel1.setLayout(new FlowLayout());
        for (int i = 0; i < btn.length; i++) {
            panel1.add(btn[i]);
        }
        panel1.setLayout(new BorderLayout());
        for (int i = 0; i < btn.length; i++) {
            panel2.add(btn[i]);
        }
        panel1.setLayout(new GridLayout());
        for (int i = 0; i < btn.length; i++) {
            panel3.add(btn[i]);
        }


        frame.pack();
        frame.setVisible(true);
        frame.setDefaultCloseOperation(frame.EXIT_ON_CLOSE);
    }
    public static void main(String[] args) {
        new No2();
    }
}

Answer 1

您正在将相同的JButton重新添加到3个JPanel中，这将无法正常工作，因为您只能将组件添加到一个容器中。在这种情况下，只有 last JPanel会显示您的按钮-您正在查找。

我将要做的是创建一个布局管理器数组，因为那是唯一更改的东西，然后在for循环中动态创建我的JPanels和按钮。查看代码中的注释：

import java.awt.BorderLayout;
import java.awt.FlowLayout;
import java.awt.GridLayout;
import java.awt.LayoutManager;    
import javax.swing.*;

@SuppressWarnings("serial")
public class No3 extends JPanel {
    private static final int BUTTON_COUNT = 5;

    // the only thing changing in each JPanel are the layouts used
    // so put them into an array
    private LayoutManager[] layouts = {
            new FlowLayout(), 
            new BorderLayout(), 
            new GridLayout()
            };

    public No3() {
        // give the enclosing JPanel a layout that holds all the other JPanels
        setLayout(new GridLayout(layouts.length, 0));
        for (LayoutManager layoutManager : layouts) {
            // create each JPanel on the fly
            JPanel panel = new JPanel(layoutManager);

            // get the title of each layout (why not?) and use it in a titled border
            String title = layoutManager.getClass().toString();
            title = title.substring(title.lastIndexOf(".") + 1);
            panel.setBorder(BorderFactory.createTitledBorder(title));

            // fill this JPanel with buttons
            for (int i = 0; i < BUTTON_COUNT; i++) {
                panel.add(new JButton("Button" + (i + 1)));
            }

            // add this panel to the main JPanel
            add(panel);
        }
    }

    private static void createAndShowGui() {
        No3 mainPanel = new No3();

        JFrame frame = new JFrame("Layout Fun GUI");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add(mainPanel);
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> createAndShowGui());
    }
}

我已经使用多个布局管理器部署了JButton，但是它无法正确显示

1 个答案: