java - 如何将内容包装在 JList 中？

Question

我有一个 JList，显示文件列表(带图标)。我使用 DefaultListCellRenderer 来完成此操作。

但是，我只希望它显示 3 列，但它显示更多。我不希望用户必须水平滚动，只能垂直滚动。我怎样才能做到这一点？我对 Java 还很陌生。

这是我到目前为止的代码:

import java.awt.Component;
import java.awt.Dimension;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Insets;
import java.io.File;
import java.io.FileFilter;

import javax.swing.DefaultListCellRenderer;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JList;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.border.EmptyBorder;
import javax.swing.filechooser.FileSystemView;

public class StartMeUpBaby extends JFrame {

    public StartMeUpBaby() {

        this.setLocationRelativeTo(null);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setTitle("TESTING");

        JPanel mainPanel = new JPanel();
        mainPanel.setLayout(new GridBagLayout());

        File f = new File(System.getProperty("user.home"));

        JList<File> results = new JList<File>(f.listFiles(new FileFilter() {

            public boolean accept(File file) {

                String name = file.getName().toLowerCase();
                return name.length() < 20;

            }

        }));

        results.setCellRenderer(new DefaultListCellRenderer() {

            public Component getListCellRendererComponent(JList<?> list, Object value, int index, boolean isSelected, boolean cellHasFocus) {

                Component component = super.getListCellRendererComponent(list, value, index, isSelected, cellHasFocus);
                JLabel label = (JLabel)component;
                File file = (File)value;

                label.setText(file.getName());
                label.setIcon(FileSystemView.getFileSystemView().getSystemIcon(file));
                label.setBorder(new EmptyBorder(3, 3, 3, 3));

                return label;

            }

        });

        results.setLayoutOrientation(JList.HORIZONTAL_WRAP);

        JScrollPane scrollPane = new JScrollPane(results, JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED, JScrollPane.HORIZONTAL_SCROLLBAR_NEVER);
        scrollPane.setPreferredSize(new Dimension(408, 100));

        GridBagConstraints gbc = new GridBagConstraints();

        gbc.gridx = 0;
        gbc.gridy = 0;

        gbc.gridwidth = 3;
        gbc.gridheight = 2;

        gbc.weightx = 100;
        gbc.weighty = 100;

        gbc.anchor = GridBagConstraints.WEST;
        gbc.fill = GridBagConstraints.HORIZONTAL;

        gbc.insets = new Insets(5, 5, 5, 5);

        mainPanel.add(scrollPane, gbc);

        this.add(mainPanel);
        this.pack();
        this.setVisible(true);

    }

    public static void main(String[] args) {

        new StartMeUpBaby();

    }

}

我将首选大小设置为仅显示 3 列，但是如果您调整窗口(使其变大)，您可以看到列继续显示。

Answer 1

来自documentation of JList.setLayoutOrientation :

HORIZONTAL_WRAP - Cells are layed out horizontally, wrapping to a new row as necessary. If the visibleRowCount property is less than or equal to zero, wrapping is determined by the width of the list; otherwise wrapping is done in such a way as to ensure visibleRowCount rows in the list.

因此，您可以通过添加以下内容来解决您的问题:

results.setVisibleRowCount(0);

但是，您的 JScrollPane 大小 (setPreferredSize(new Dimension(488, 100))) 是任意的。显示三列所需的大小取决于显示的文件名以及 JList 字体等视觉属性。即使存在一个相当长的文件名，单元格也会变宽，并且您的大小可能不够。

为了完全稳健，您需要根据每个文件的渲染计算首选大小:

File f = new File(System.getProperty("user.home"));

File[] files = f.listFiles(new FileFilter() {

    public boolean accept(File file) {

        String name = file.getName().toLowerCase();
        return name.length() < 20;

    }

});

JList<File> results = new JList<File>(files) {
    private Dimension maxCellSize = new Dimension();

    @Override
    public void addNotify() {
        super.addNotify();
        recomputeMaxCellSize();
    }

    private void recomputeMaxCellSize() {
        ListCellRenderer<? super File> renderer = getCellRenderer();
        if (renderer == null) {
            return;
        }

        int fixedWidth = getFixedCellWidth();
        int fixedHeight = getFixedCellHeight();

        Rectangle maxCellBounds = new Rectangle();
        for (int i = getModel().getSize() - 1; i >= 0; i--) {
            Component c =
                renderer.getListCellRendererComponent(this,
                    getModel().getElementAt(i), i, false, false);
            Dimension cellSize = c.getPreferredSize();
            maxCellBounds.add(
                fixedWidth >= 0 ? fixedWidth : cellSize.width,
                fixedHeight >= 0 ? fixedHeight : cellSize.height);
        }

        maxCellSize = maxCellBounds.getSize();
    }

    @Override
    public Dimension getPreferredSize() {
        int count = getModel().getSize();
        int rows = count / 3 + (count % 3 == 0 ? 0 : 1);

        return new Dimension(maxCellSize.width * 3,
                             maxCellSize.height * rows);
    }

    @Override
    public Dimension getPreferredScrollableViewportSize() {
        int rows = getVisibleRowCount();
        if (rows <= 0) {
            rows = 4;
        }

        return new Dimension(maxCellSize.width * 3,
                             maxCellSize.height * rows);
    }

    private final ListDataListener modelListener = new ListDataListener() {
        @Override
        public void intervalAdded(ListDataEvent event) {
            recomputeMaxCellSize();
        }

        @Override
        public void intervalRemoved(ListDataEvent event) {
            recomputeMaxCellSize();
        }

        @Override
        public void contentsChanged(ListDataEvent event) {
            recomputeMaxCellSize();
        }
    };

    @Override
    public void setModel(ListModel<File> newModel) {
        getModel().removeListDataListener(modelListener);
        newModel.addListDataListener(modelListener);
        super.setModel(newModel);
        recomputeMaxCellSize();
    }

    @Override
    public void setCellRenderer(ListCellRenderer<? super File> renderer) {
        super.setCellRenderer(renderer);
        recomputeMaxCellSize();
    }

    @Override
    public void setFont(Font font) {
        super.setFont(font);
        recomputeMaxCellSize();
    }

    @Override
    public void setFixedCellWidth(int width) {
        super.setFixedCellWidth(width);
        recomputeMaxCellSize();
    }

    @Override
    public void setFixedCellHeight(int height) {
        super.setFixedCellHeight(height);
        recomputeMaxCellSize();
    }
};

results.setVisibleRowCount(0);