如何将组件动态添加到Java JScrollPane

Question

我正在尝试用Java创建一个GUI应用程序但是我在JScrollPane中动态添加/更新组件时遇到了麻烦。我有两个JPanel（P1和P2），其中P1有一个表单来设置应用程序的参数，P2包含一些GUI组件，它们根据P1中的值动态更新。我需要在P2上滚动JScrollPane，所以我在P2中添加了JScrollPane。我将P1和P2添加到主面板“main”，然后将主面板添加到框架中。但是P2中没有更新组件。有人可以提出什么问题吗？我调用了revalidate（），repaint（）和其他一些方法，但GUI没有更新。下面是我编写的示例代码，用于说明我的问题。我在我的应用程序中需要GroupLayout，所以在这里我也使用了GroupLayout

        import java.awt.event.ActionEvent;
        import javax.swing.GroupLayout;
        import javax.swing.JButton;
        import javax.swing.JFrame;
        import javax.swing.JPanel;
        import javax.swing.JScrollPane;


        public class JframeExample extends JFrame {

            private final JPanel P1;
            private final JPanel P2;
            private final JPanel main;
            private final JScrollPane scrol;
            private final JButton jButton;
            private final JButton jButton2;

            public JframeExample() {
                P1 = new JPanel();
                P2 = new JPanel();
                main = new JPanel();
                jButton = new JButton("Add");
                jButton2 = new JButton("Remove");
                scrol = new JScrollPane();
                initialize();
                this.add(main);
                this.setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
                this.setSize(400, 400);
                this.setVisible(true);

            }

            public static void main(String[] args) {
                JframeExample jframeExample = new JframeExample();

            }

            private void addPressed(ActionEvent evt) {
                System.out.println("Add Pressed");
                scrol.add(new JButton());
                revalidate();
            }

            private void removePressed(ActionEvent evt) {
                System.out.println("Remove Pressed");
                scrol.removeAll();
                revalidate();
            }

            private void initialize() {
                GroupLayout layout = new GroupLayout(P1);
                P1.setLayout(layout);
                layout.setAutoCreateGaps(true);
                layout.setAutoCreateContainerGaps(true);
                GroupLayout.SequentialGroup hGroup = layout.createSequentialGroup();
                hGroup.addGroup(layout.createParallelGroup(GroupLayout.Alignment.TRAILING)
                        .addComponent(jButton).addComponent(jButton2));

                layout.setHorizontalGroup(hGroup);
                GroupLayout.SequentialGroup vGroup = layout.createSequentialGroup();
                vGroup.addGroup(layout.createParallelGroup(GroupLayout.Alignment.BASELINE).addComponent(jButton))
                        .addGroup(layout.createParallelGroup(GroupLayout.Alignment.BASELINE).addComponent(jButton2));
                layout.setVerticalGroup(vGroup);
                P2.add(scrol);
                jButton.addActionListener((ActionEvent evt) -> {
                    addPressed(evt);
                });
                jButton2.addActionListener((ActionEvent evt) -> {
                    removePressed(evt);
                });
                GroupLayout layoutMain = new GroupLayout(main);
                main.setLayout(layoutMain);
                layoutMain.setAutoCreateGaps(true);
                layoutMain.setAutoCreateContainerGaps(true);
                layoutMain.setHorizontalGroup(layoutMain.createSequentialGroup()
                        .addComponent(P1).addComponent(P2));
                layoutMain.setVerticalGroup(layoutMain
                        .createParallelGroup(GroupLayout.Alignment.BASELINE).addComponent(P1)
                        .addComponent(P2));

            }

        }

Answer 1

  

在JScrollPane中包装P2也不起作用。

是的，因为这是它的工作方式。如果您花时间阅读How to use scroll panes，请查看示例，甚至可以参考JavaDocs它将为您提供启动和运行UI所需的基本信息。

import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;

public class JframeExample extends JFrame {

    private final JPanel P1;
    private final JPanel P2;
    private final JPanel main;
    private final JScrollPane scrol;
    private final JButton jButton;
    private final JButton jButton2;

    public JframeExample() {
        P1 = new JPanel();
        P2 = new JPanel();
        main = new JPanel();
        jButton = new JButton("Add");
        jButton2 = new JButton("Remove");
        scrol = new JScrollPane(P2);
        initialize();
        this.add(main);
        this.setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        this.setSize(400, 400);
        this.setVisible(true);

    }

    public static void main(String[] args) {
        JframeExample jframeExample = new JframeExample();

    }

    private void addPressed(ActionEvent evt) {
        System.out.println("Add Pressed");
        P2.add(new JButton());
        revalidate();
    }

    private void removePressed(ActionEvent evt) {
        System.out.println("Remove Pressed");
        P2.removeAll();
        revalidate();
    }

    private void initialize() {
        main.setLayout(new GridLayout(1, 2));
        main.add(P1);
        main.add(scrol);
        jButton.addActionListener((ActionEvent evt) -> {
            addPressed(evt);
        });
        jButton2.addActionListener((ActionEvent evt) -> {
            removePressed(evt);
        });
        P1.add(jButton);
        P1.add(jButton2);
    }

}

警告语GroupLayout实际上不适用于手工编码，它实际上是为UI编辑设计的。