java - 更改流程布局中的面板大小

Question

我正在用java开发一个GUI表单。我在主框架中添加了两个具有 FlowLayout 的面板。但现在我想更改面板的大小，我尝试使用 setsize() 进行更改，但我看不出有什么区别。

这是我的代码:

public class Main_window extends JFrame implements ActionListener {

    JFrame MainFrm = new JFrame("MCQ Generator");
    JPanel LeftPanel = new JPanel();
    JPanel RightPanel = new JPanel();
    JButton BrowseButton = new JButton("Browse/Open");
    TextArea ta1 = new TextArea();
    TextArea ta2 = new TextArea();
    JButton ClearWindow = new JButton("Clear Window");
    JButton generateButton = new JButton("Generate MCQs");
    String fname;

    Main_window() {
        MainFrm.setLayout(new FlowLayout(FlowLayout.LEFT));
        MainFrm.setSize(1050, 400);
        MainFrm.add(LeftPanel, FlowLayout.LEFT);
        MainFrm.add(RightPanel);
        LeftPanel.setLayout(new BorderLayout(30, 30));
    //LeftPanel.setSize(10, 10);
        //RightPanel.setSize(10, 10);
        RightPanel.setLayout(new BorderLayout(40, 40));
        LeftPanel.setOpaque(true);
        LeftPanel.setBackground(Color.LIGHT_GRAY);
        LeftPanel.setBorder(BorderFactory.createEmptyBorder(10, 10, 10, 10));
        RightPanel.setOpaque(true);
        RightPanel.setBackground(Color.LIGHT_GRAY);
        RightPanel.setBorder(BorderFactory.createEmptyBorder(10, 10, 10, 10));
        JPanel InnerPanel = new JPanel();
        InnerPanel.setLayout(new FlowLayout());
        InnerPanel.setBackground(Color.LIGHT_GRAY);
        InnerPanel.add(new JLabel("Choose File: "));
        LeftPanel.add(InnerPanel, BorderLayout.NORTH);
        LeftPanel.add(ta1, BorderLayout.CENTER);
        RightPanel.add(new JLabel("Questions Generated:"), BorderLayout.NORTH);
        RightPanel.add(ta2, BorderLayout.CENTER);
    //ta1.setSize(10, 100);
        //ta2.setSize(10, 100);
        BrowseButton.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {

                JFileChooser chooser = new JFileChooser();
                FileNameExtensionFilter filter = new FileNameExtensionFilter(
                        "Text Documents(*.txt)", "txt");
                chooser.setFileFilter(filter);
                int returnVal = chooser.showOpenDialog(LeftPanel);
                if (returnVal == JFileChooser.APPROVE_OPTION) {
                    System.out.println("You choose to open this file: " + chooser.getCurrentDirectory() + "\\" + chooser.getSelectedFile().getName());
                    fname = new String(chooser.getCurrentDirectory() + "\\" + chooser.getSelectedFile().getName());
                    try {
                        Jdbc_conn.truncateInputTable(ta1);
                        displayInput(fname);
                        //Jdbc_conn.truncateInputTable(ta1);
                        Give_input.getInput(fname);
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
            }

        });
        InnerPanel.add(BrowseButton);
        LeftPanel.add(generateButton, BorderLayout.SOUTH);
        generateButton.addActionListener(this);
        RightPanel.add(ClearWindow, BorderLayout.SOUTH);
        ClearWindow.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent ae) {
                try {
                    Jdbc_conn.truncateMcqAndNew_nountab(ta2);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
        MainFrm.setVisible(true);
        MainFrm.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }

Answer 1

通常，当 setSize() 不起作用时，请尝试使用 setPreferredSize()。

在本例中，如 Oracle tutorial说:“FlowLayout 类将组件放在一行中，按其首选大小调整大小。如果容器中的水平空间太小而无法将所有组件放在一行中，则 FlowLayout 类使用多行。如果容器比一行组件所需的宽度宽，则默认情况下，该行在容器内水平居中。要指定该行向左或向右对齐，请使用 FlowLayout 构造函数采用对齐参数。FlowLayout 类的另一个构造函数指定组件周围放置多少垂直或水平填充。”