Java : Why doesn't this scrollpane scroll?

Question

我有这个类(class)作为我的问题的一个例子。滚动 Pane 不滚动，我看不出一个很好的理由:

    import java.awt.Dimension;

import javax.swing.JOptionPane;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;


public class DoesNotScroll{ 

    public static void main(String[] args){
        String str = "this\n\nshould\n\n\n\nscroll\n\n\nthis is the bottom";
        message("test", str, JOptionPane.INFORMATION_MESSAGE);
    }

    public final static void message(String title, String message, int messageType){
        JTextArea messageArea = new JTextArea();
        messageArea.setMinimumSize(new Dimension(300, 100));
        messageArea.setMaximumSize(new Dimension(300, 100));
        messageArea.setPreferredSize(new Dimension(300, 100));
        messageArea.setEditable(false);
        JScrollPane scroller = new JScrollPane(messageArea);
        scroller.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
        scroller.setHorizontalScrollBarPolicy(JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);
        messageArea.setText(message);
        messageArea.revalidate();
        messageArea.repaint();
        JOptionPane.showMessageDialog(null, scroller, title, messageType);
    }
}

感谢任何帮助，

-C

Answer 1

The problem with my setup here was that I was calling messageArea.setPreferredSize() instead of scroller.setPreferredSize()

在这种情况下，需要调用其中任何一个都表明存在问题。通过在构造函数中提供列/行大小来设置文本区域的“首选大小”。将其添加到滚动 Pane 中。工作完成。

import javax.swing.*;

public class DoesScroll {

    public static void main(String[] args){
        String str = "this\n\nshould\n\n\n\nscroll\n\n\nthis is the bottom";
        message("test", str, JOptionPane.INFORMATION_MESSAGE);
    }

    public final static void message(String title, String message, int messageType){
        JTextArea messageArea = new JTextArea(3,20);
        messageArea.setEditable(false);
        JScrollPane scroller = new JScrollPane(messageArea,
            JScrollPane.VERTICAL_SCROLLBAR_ALWAYS,
            JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);
        messageArea.setText(message);
        JOptionPane.showMessageDialog(null, scroller, title, messageType);
    }
}