Java JTextPane 在添加 UTF8 字符时更改行高

Question

I am using Java JDK 1.6 and have a problem using JTextPane to show text with a monospaced font. As soon as I add a UTF8-character like, the line height in the textpane is reduced (for all the text already in the pane and also all text added later). How can I avoid this? I would like to have the normal line height.

Here is some sample code:

    class AttributedTextPane extends JTextPane
    {

        private DefaultStyledDocument defaultStyledDocument;

        protected AttributedTextPane()
        {
            this.defaultStyledDocument = new DefaultStyledDocument();
            this.setDocument(defaultStyledDocument);

            this.setContentType("text/plain");
            ...
        }
    }
    ...

This pane is integrated into an JInternalFrame. Creating the panel and setting the desired monospaced font:

    Font font = new Font("DejaVu Sans Mono", Font.PLAIN, 11);
    AttributedTextPane pane = new AttributedTextPane();
    pane.setFont(font);

To display the desired text, I call pane.setText(...); As soon as I add the UTF8 character, the line height changes, see screenshot at http://i.imgur.com/Fq7XBJB.png . Is there a way to avoid that the line height is changed? Thanks, Deejay

Answer 1

You could try setting/forcing a line height like so:

MutableAttributeSet jTextPaneSet = new SimpleAttributeSet(pane.getParagraphAttributes());
StyleConstants.setLineSpacing(jTextPaneSet, 1.5f); //replace float 1.5f with your desired line spacing/height

Source:

http://docs.oracle.com/javase/8/docs/api/javax/swing/JTextPane.html#setParagraphAttributes(javax.swing.text.AttributeSet,%20boolean)

https://docs.oracle.com/javase/7/docs/api/javax/swing/text/StyleConstants.html#setLineSpacing(javax.swing.text.MutableAttributeSet,%20float)

Answer 2

Old question but I have been struggling with it for some time, though with a JTextArea. The solution is to have either a VM param -Di18n=true or put the i18n property in the document.

My test code:

import javax.swing.JTextArea;

public class Test {
    public static void main(String[] argv) {
        JTextArea ta = new JTextArea();
        //ta.getDocument().putProperty("i18n", Boolean.TRUE);
        ta.setText("A");
        System.out.println(ta.getPreferredSize()); // - height 16 without i18n and using default font, 15 with i18n
        ta.setText("\ud8ff\udc05"); // surrogate pair
        System.out.println(ta.getPreferredSize()); // - height 15
        ta.setText("A");
        System.out.println(ta.getPreferredSize()); // - height 15
    }
}

When i18n is not enabled and the document is appended, the elements that are created are PlainView/WrappedPlainView that return the height based on the FontMetrics height.

When i18n is enabled the elements are PlainParagraph that contain GlyphView that calculates the height differently.

When i18n is not enabled and the document is appended with a surrogate pair then due to SwingUtilities2.isComplexLayout returning true, the i18n property is automatically set to true for the document and then all elements are created as PlainParagraph containing GlyphView that return the different (always smaller?) height.