当 space 足以显示内容时，JScrollPane 不会顶部对齐

Question

我有一个显示项目列表的 JScrollPane。如果屏幕上没有足够的 space 来显示列表，我希望用户能够滚动列表，我希望列表与可用 space 的顶部对齐，如果space 足以显示列表。我可以做一个或另一个，但似乎无法同时工作。如果列表大于可用 space 但未与顶部对齐，则下面显示的代码实现了允许列表滚动的目标，如下所示。我已经尝试过将 JScrollPane 放在 borderlayout 的北部部分，但是当我这样做时，列表不再可滚动（即 borderlayout 为滚动窗格提供了它需要的所有 space 并且列表现在不可滚动).

下面是代码创建的内容：

这是代码：

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.GridLayout;

import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;

public class Example {

    public static void main(String[] args) {
        JFrame jFrame = new JFrame();
        jFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        jFrame.setSize(400, 200);
        // main panel
        JPanel pan = new JPanel();
        pan.setLayout(new GridLayout(1, 2));
        pan.setBackground(Color.BLUE);
        jFrame.getContentPane().add(pan, BorderLayout.CENTER);
        jFrame.show();
        // left panel
        JPanel left = getContentPanel();
        left.setBackground(Color.ORANGE);
        pan.add(left);
        // right panel (with scroll pane)
        JPanel right = getContentPanel();
        right.setBackground(Color.YELLOW);
        JScrollPane scr = new JScrollPane(right);
        scr.setBackground(Color.CYAN);
        scr.setAlignmentX(JScrollPane.LEFT_ALIGNMENT);
        scr.setAlignmentY(JScrollPane.TOP_ALIGNMENT);
        pan.add(scr);
    }

    private static JPanel getContentPanel() {
        JPanel rtn = new JPanel();
        rtn.setLayout(new GridBagLayout());
        GridBagConstraints cs = new GridBagConstraints();
        cs.gridx = 0;
        cs.weightx = 1;
        cs.anchor = GridBagConstraints.NORTHWEST;
        for (int i = 0; i < 20; i++) {
            JLabel label = new JLabel("Item " + (i + 1));
            label.setBackground(Color.DARK_GRAY);
            cs.gridy = i;
            rtn.add(label, cs);
        }
        rtn.setBackground(Color.GREEN);
        return rtn;
    }

}

Answer 1

您可以使用 Boxlayout。

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.GridLayout;

import javax.swing.Box;
import javax.swing.BoxLayout;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;

public class Example {

    public static void main(String[] args) {
        JFrame jFrame = new JFrame();
        jFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        jFrame.setSize(400, 200);
        // main panel
        JPanel pan = new JPanel();
        pan.setLayout(new GridLayout(1, 2));
        pan.setBackground(Color.BLUE);
        jFrame.getContentPane().add(pan, BorderLayout.CENTER);
        jFrame.show();
        // left panel
        JPanel left = getContentPanel();
        left.setBackground(Color.ORANGE);
        pan.add(left);
        // right panel (with scroll pane)
        JPanel right = getContentPanel();
        right.setBackground(Color.YELLOW);
        JScrollPane scr = new JScrollPane(right);
        scr.setBackground(Color.CYAN);
        scr.setAlignmentX(JScrollPane.LEFT_ALIGNMENT);
        scr.setAlignmentY(JScrollPane.TOP_ALIGNMENT);
        pan.add(scr);
    }

    private static JPanel getContentPanel() {
        JPanel rtn = new JPanel();

        rtn.setLayout(new BoxLayout(rtn, BoxLayout.Y_AXIS));

        for (int i = 0; i < 20; i++) {
            JLabel label = new JLabel("Item " + (i + 1));
            label.setBackground(Color.DARK_GRAY);
            rtn.add(label);
        }

        rtn.add(Box.createVerticalGlue());

        rtn.setBackground(Color.GREEN);
        return rtn;
    }

}

当 space 足以显示内容时，JScrollPane 不会顶部对齐

JScrollPane doesn't top align when there is more than enough space to show the content

java

swing

jscrollpane

layout-manager