JScrollPane中的Java JPanel？

Question

我有一个JFrame,在这个JFrame中我有一个我绘制的JPanel,这个面板可以是任何大小,所以我将它放入一个JScrollpane让我在面板大于窗口屏幕大小时滚动.

不幸的是,我的预期不起作用:

1. 使JFrame窗口小于JPanel大小不会显示滚动条

2. JScrollPane大小现在似乎锁定了我添加到它的JPanel的大小,之前它调整到它的JFrame窗口的边界(它仍然有点这样但现在只是垂直？!)

3. 无论我为首选大小设置什么,JPanel似乎都假设JScrollpane的大小

我确信我做的事情很愚蠢,如果有人能指出我会非常感激的话!

JPanel _ImageCanvas = new JPanel(); // 'Canvas' to draw on
JScrollPane _ScrollPane = new JScrollPane();

// set size of 'canvas'
_ImageCanvas.setMinimumSize(new Dimension(100,100));

// Scroll pane smaller then the size of the canvas so we should get scroll bars right?
_ScrollPane.setMinimumSize(new Dimension(50,50)); 

// Add a border to 'canvas'
_ImageCanvas.setBorder(BorderFactory.createLineBorder(new java.awt.Color(0, 0, 0)));

_ScrollPane.setViewportView(JPanel);

非常感谢

大卫

Answer 1

setPreferredSize()是技巧,JSMrollPane将忽略组件上的setMinimumSize()甚至setSize().这是一个使用红色边框的工作示例.

import java.awt.*;

import javax.swing.*;

public class Scroller extends JFrame {

    public Scroller() throws HeadlessException {
        final JPanel panel = new JPanel();
        panel.setBorder(BorderFactory.createLineBorder(Color.red));
        panel.setPreferredSize(new Dimension(800, 600));

        final JScrollPane scroll = new JScrollPane(panel);

        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLayout(new BorderLayout());
        add(scroll, BorderLayout.CENTER);
        setSize(300, 300);
        setVisible(true);
    }

    public static void main(final String[] args) throws Exception {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                new Scroller().setVisible(true);
            }
        });
    }
}

Answer 2

// suggest a size of 'canvas'
_ImageCanvas.setPreferredSize(new Dimension(100,100));

// Scroll pane smaller then the size of the canvas so we should get scroll bars right?
_ScrollPane.setPreferredSize(new Dimension(50,50)); 

// ..later 
_Frame.pack();