如何动态添加元素到JScrollPanel？

Question

我正在尝试使用Java中的Swing制作一个GUI，它可以执行以下操作：

当按下“添加”按钮时，会创建一个JPanel，并填满图形用户界面的整个宽度。在JPanel中，JLabels将使用FlowLayout来排列，该FlowLayout告诉特定的细节（例如名称、用户ID等）。每当随后按下添加按钮时，我都希望在前面的按钮下添加一个新的JPanel，以便JScrollPane在必要时激活其垂直滚动条。基本上，我希望JScrollPane能够在其中动态添加新的JPanels。

然而，我在尝试这样做时遇到了一些问题。在JScrollPane中，我无法确定要为面板使用哪个LayoutManager。我尝试过使用GridlLayout，但这似乎不起作用，因为当有足够多的JPanel覆盖整个JScrollPane时，GridLayout只会创建一个新列，在新的JPanel中挤压，而不是将其添加到以前的JPanel下面。为了实现这一目标，我应该做些什么？以下是我所拥有的一些图片和我希望发生的事情的一个例子。

以下是我希望发生的事情：

任何帮助将不胜感激，提前感谢！：）

编辑：下面是我用GridLayout尝试的代码示例。

public Window() {


    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setBounds(100, 100, 701, 400);
    contentPane = new JPanel();
    contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
    contentPane.setLayout(new BorderLayout(0, 0));
    setContentPane(contentPane);

    JPanel buttonPanel = new JPanel();
    contentPane.add(buttonPanel, BorderLayout.SOUTH);

    JButton btnAdd = new JButton("Add");
    buttonPanel.add(btnAdd);

    JScrollPane scrollPane = new JScrollPane();
    contentPane.add(scrollPane, BorderLayout.CENTER);

    JPanel systemsPanel = new JPanel();
    scrollPane.setViewportView(systemsPanel);
    systemsPanel.setLayout(new GridLayout(8, 1, 0, 0)); //8 rows for now



    for (int i = 1; i < 50; i++) {
        systemsPanel.add(new JButton("test"), "cell 0 " + i);
    }
    Dimension dim = Toolkit.getDefaultToolkit().getScreenSize();
    this.setLocation(dim.width / 2 - this.getSize().width / 2, dim.height / 2 - this.getSize().height / 2); //Center the Frame 

}

Answer 1

如果您想将行JPanel添加到GUI中，我会将它们放在使用GridLayout（0，1）或（0，1，x，y）的JPanel中。0表示行数可变，1表示1列，x和y表示垂直和水平间隙。然后，我将使用JPanel将其放置到BorderLayout中的NORTH位置，这样行就不会像它们希望的那样展开以填充scrollpane的视口。我将第二个包装器JPanel放入JScrollPane的视口中。

添加任何组件后，我将调用容器上的revalidate和repait，以便其布局管理器能够激活并正确放置新组件，并重新绘制以去除可能挂起的任何脏像素（在移除组件时更为重要）。

例如，我的MCVE：

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;

import javax.swing.*;

public class AddRowA extends JPanel {
    private static final int PREF_W = 650;
    private static final int PREF_H = 400;

    // JPanel to hold all rows. uses gridlayout that has 1 column and variable number
    // of rows
    private JPanel rowHolderPanel = new JPanel(new GridLayout(0, 1, 1, 1));

    public AddRowA() {
        // outerPanel is a wrapper or container JPanel that is 
        // held by JScrollPane's viewport that holds the rowHolderPanel in 
        // a BorderLayout.PAGE_START location, so the rows don't expand unnecessarily
        JPanel outerPanel = new JPanel(new BorderLayout());
        outerPanel.add(rowHolderPanel, BorderLayout.PAGE_START);
        JScrollPane scrollPane = new JScrollPane(outerPanel);
        scrollPane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);

        JPanel addPanel = new JPanel();
        addPanel.add(new JButton(new AddAction("Add")));

        setLayout(new BorderLayout());
        add(scrollPane, BorderLayout.CENTER);
        add(addPanel, BorderLayout.PAGE_END);
    }

    @Override
    public Dimension getPreferredSize() {
        if (isPreferredSizeSet()) {
            return super.getPreferredSize();
        }
        return new Dimension(PREF_W, PREF_H);
    }

    private class AddAction extends AbstractAction {
        public AddAction(String name) {
            super(name);
            int mnemonic = (int) name.charAt(0);
            putValue(MNEMONIC_KEY, mnemonic);
        }

        @Override
        public void actionPerformed(ActionEvent e) {
            JPanel panel = new JPanel();
            panel.add(new JLabel("Foo"));
            panel.add(Box.createHorizontalStrut(25));
            panel.add(new JButton("Bar"));
            panel.setBorder(BorderFactory.createLineBorder(Color.BLACK, 3));

            rowHolderPanel.add(panel);
            rowHolderPanel.revalidate();
            rowHolderPanel.repaint();
        }
    }

    private static void createAndShowGui() {
        JFrame frame = new JFrame("Add Row A");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add(new AddRowA());
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

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

但是，你最好使用JTable。。。例如：

import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import javax.swing.*;
import javax.swing.table.DefaultTableModel;

public class AddRowB extends JPanel {
    private MyTableModel tableModel = new MyTableModel();
    private JTable table = new JTable(tableModel);

    public AddRowB() {
        JPanel addPanel = new JPanel();
        addPanel.add(new JButton(new AddAction("Add")));

        setLayout(new BorderLayout());
        add(new JScrollPane(table));
        add(addPanel, BorderLayout.PAGE_END);
    }

    private class AddAction extends AbstractAction {
        public AddAction(String name) {
            super(name);
            int mnemonic = (int) name.charAt(0);
            putValue(MNEMONIC_KEY, mnemonic);
        }

        @Override
        public void actionPerformed(ActionEvent e) {
            RowData row = new RowData("Type", "Address", "User ID");
            tableModel.addRow(row);
        }
    }

    private static void createAndShowGui() {
        JFrame frame = new JFrame("Add Row B");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add(new AddRowB());
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

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

class MyTableModel extends DefaultTableModel {
    private static final String[] COLUMNS = {"Type", "Address", "User ID"};

    public MyTableModel() {
        super(COLUMNS, 0);
    }

    public void addRow(RowData rowData) {
        Object[] row = {
                rowData.getType(),
                rowData.getAddress(),
                rowData.getUserID()
        };
        addRow(row);
    }
}

class RowData {
    String type;
    String address;
    String userID;

    public RowData(String type, String address, String userID) {
        this.type = type;
        this.address = address;
        this.userID = userID;
    }

    public String getType() {
        return type;
    }

    public String getAddress() {
        return address;
    }

    public String getUserID() {
        return userID;
    }

}