使用Nimbus Look And Feel时,无法在JTextArea背景上绘制图像

Question

我在JTextArea背景上绘制图像,它使用其他外观和感觉(金属,Windows等)绘制,但当我使用Nimbus外观和感觉它不绘制图像可能的问题是什么以及如何解决这个问题？这是我正在使用的代码

Image TextArea类

public class ImageTextArea extends JTextArea{
    File image;
    public ImageTextArea(File image)
    {
        setOpaque(false);
        this.image=image;
    }

    @Override
    public void paintComponent(final Graphics g)
    {
        try
        {
            // Scale the image to fit by specifying width,height
            g.drawImage(new ImageIcon(image.getAbsolutePath()).getImage(),0,0,getWidth(),getHeight(),this);
            super.paintComponent(g);
        }catch(Exception e){}
    }
}

和Test类

public class TestImageTextArea extends javax.swing.JFrame {

    private ImageTextArea tx;

    public TestImageTextArea() {
        tx = new ImageTextArea(new File("img.jpg"));
        setTitle("this is a jtextarea with image");
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        JPanel mainp = new JPanel(new BorderLayout());
        add(mainp);
        mainp.add(new JScrollPane(tx), BorderLayout.CENTER);
        setSize(400, 400);
    }

    public static void main(String args[]) {
/*
        try {
            for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
                if ("Nimbus".equals(info.getName())) {
                    javax.swing.UIManager.setLookAndFeel(info.getClassName());
                    break;
                }
            }
        } catch (Exception ex) {
            System.out.println("Unable to use Nimbus LnF: "+ex);
        }
*/
        java.awt.EventQueue.invokeLater(new Runnable() {

            public void run() {
                new TestImageTextArea().setVisible(true);
            }
        });
    }

}

当我删除评论时,它不会绘制图像.

Answer 1

基本上,当你打电话时super.paintComponent,它会调用UI delgate的update方法.这就是魔术发生的地方.

以下是Nimbus的SynthTextAreaUI实施

public void update(Graphics g, JComponent c) {
    SynthContext context = getContext(c);

    SynthLookAndFeel.update(context, g);
    context.getPainter().paintTextAreaBackground(context,
                      g, 0, 0, c.getWidth(), c.getHeight());
    paint(context, g);
    context.dispose();
}

正如您所看到的,它实际上绘制了背景,不考虑组件的不透明状态,然后调用paint,这将调用BasicTextUI.paint方法(via super.paint)

这很重要,因为BasicTextUI.paint实际绘制文本.

那么,这对我们有什么帮助？通常情况下,我会因为没有打电话super.paintComponent而将某人钉在十字架上,但这正是我们要做的事情,但我们会提前知道我们正在承担什么样的责任.

首先,我们将接管责任update,填写背景,绘制背景,然后调用paintUI代表.

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.imageio.ImageIO;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class NimbusTest {

    public static void main(String[] args) {
        new NimbusTest();
    }

    public NimbusTest() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel("com.sun.java.swing.plaf.nimbus.NimbusLookAndFeel");
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                }

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                frame.add(new JScrollPane(new TestTextArea()));
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestTextArea extends JTextArea {

        private BufferedImage bg;

        public TestTextArea() {
            try {
                bg = ImageIO.read(new File("C:\\Users\\swhitehead\\Documents\\My Dropbox\\Ponies\\Rainbow_Dash_flying_past_3_S2E16.png"));
            } catch (IOException ex) {
                Logger.getLogger(NimbusTest.class.getName()).log(Level.SEVERE, null, ex);
            }
        }

        @Override
        protected void paintComponent(Graphics g) {
            Graphics2D g2d = (Graphics2D) g.create();
            // Fill the background, this is VERY important
            // fail to do this and you will have major problems
            g2d.setColor(getBackground());
            g2d.fillRect(0, 0, getWidth(), getHeight());
            // Draw the background
            g2d.drawImage(bg, 0, 0, this);
            // Paint the component content, ie the text
            getUI().paint(g2d, this);
            g2d.dispose();
        }

    }
}

不犯错误.如果你没有做到这一点,它不仅会拧紧这个组件,而且可能会屏幕上的大多数其他组件.