Question

我正在尝试将JList添加到JPanel。具体来说，我有两个JPanels，一个是右边的，另一个是左边的。右边有两个按钮。在左边我想要JList mySpriteOptions（参见下面的代码）。不幸的是，当我运行我的代码时，这个JList永远不会出现。我不是摇摆专家（实际上我是一个巨大的新手）所以我无法弄清楚为什么会这样。

这是我的代码：

    import java.awt.*;
    import java.swing.*


    public class SpriteEditorLauncher extends JFrame {

    private JLabel mySearchBoxLabel;
    private JList mySpriteOptions;
    private JPanel myLeft;
    private JPanel myRight;
    private JScrollPane myScrollPane;
    private JTextField mySearchBox;
    private JButton myNewEditLauncher;
    private JButton myEditLauncher;

    private static final long serialVersionUID = 1L;
    private static final String FONT_TYPE = "Times New Roman";
    private static final int FONT_SIZE = 12;
    private static final int FONT_STYLE = 1;
    private static final Font FONT = new Font(FONT_TYPE, FONT_STYLE, FONT_SIZE);
    private static final int NUMBER_OF_ROWS = 1;
    private static final int NUMBER_OF_COLUMNS = 2;
    private static final int FRAME_WIDTH = 600;
    private static final int FRAME_HEIGHT = 400;

    public SpriteEditorLauncher () {
        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        initializeComponents();
        createLayout();
    }

    private void initializeComponents () {
        myLeft = new JPanel();
        myRight = new JPanel();
        myNewEditLauncher = new JButton();
        myEditLauncher = new JButton();
        myScrollPane = new JScrollPane();
        mySpriteOptions = new JList();
        mySearchBox = new JTextField();
        mySearchBoxLabel = new JLabel();

    }

    private void setPanelBorder (JPanel toSetBorderFor) {
        toSetBorderFor.setBorder(BorderFactory
                .createTitledBorder(null, "Options", TitledBorder.DEFAULT_JUSTIFICATION,
                                    TitledBorder.DEFAULT_POSITION, FONT));
    }

    private void setButtonLabel (JButton button, Font font, String label) {
        button.setFont(font);
        button.setText(label);
    }

    private void setFrameLayout () {
        GridLayout myLayout = new GridLayout(NUMBER_OF_ROWS, NUMBER_OF_COLUMNS);
        setLayout (myLayout);
        setPreferredSize(new Dimension(FRAME_WIDTH, FRAME_HEIGHT));
        setResizable(false);
    }

    private void addPanelsToFrame () {
        add(myLeft);
        add(myRight);
    }

    private void addButtonsToPanel (JPanel panel) {
        panel.add(myNewEditLauncher);
        panel.add(myEditLauncher);
    }



    private void createLayout () {

        setFrameLayout();
        setPanelBorder(myRight);
        setButtonLabel(myNewEditLauncher, FONT, "New");
        setButtonLabel(myEditLauncher, FONT, "Edit");

        addPanelsToFrame();

        addButtonsToPanel(myRight);



        mySpriteOptions.setModel(new AbstractListModel() {

            private static final long serialVersionUID = 1L;
            String[] strings = { "Item 1", "Item 2"};

            public int getSize () {
                return strings.length;
            }

            public Object getElementAt (int i) {
                return strings[i];
            }
        });

        myLeft.add(mySpriteOptions);

        myScrollPane.setViewportView(mySpriteOptions);

        mySearchBox.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed (ActionEvent arg0) {
                // TODO Auto-generated method stub

            }
        });

        mySearchBoxLabel.setFont(FONT);
        mySearchBoxLabel.setLabelFor(mySearchBox);
        mySearchBoxLabel.setText("Search:");

        pack();
        setVisible(true);
    }

}

Answer 1

JPanel的默认布局为FlowLayout。

FlowLayout喜欢使用其首选组件的大小来布局它们。

空JList的默认大小可能是0x0，这意味着它永远不会出现。

尝试使用BorderLayout（myRight = new JPanel(new BorderLayout());）创建右侧面板，并将JList添加到其中，包含在JScrollPane ...

中

private void addPanelsToFrame () {
    add(myLeft);
    add(new JScrollPane(myRight));
}

看看

了解更多信息

Answer 2

您永远不会将myScrollPane添加到JPanel myLeft：

myLeft.add(myScrollPane);

虽然您已将mySpriteOptions添加到myLeft，但它也设置为ViewportView的{{1}}。

组件只会被涂在它附加的 last 容器上 - 所以仅会出现在myScrollPane中，但尚未添加。

现在，不需要此声明：

JScrollPane

将JList添加到JPanel

2 个答案: