自制JAVA打印预览JDialog打开后无法及时显示打印图片

Question

初学JAVA，在做一个打印预览的练习
在打开这个打印预览的JDialog后，页面显示正常，但是需要打印的图片无法及时显示出来
应该是draw在canvas里面了，但是没有显示出来，如果我打开其它窗口再回到这个JDialog图片才会出来
页面设置后图片能正常显示，就是在最初打开窗体时，图片无法正常显示出来代码如下：
import java.net.*;
import java.awt.*;
import java.awt.event.*;
import java.awt.print.*;
import javax.swing.*;
public class PrintPreview extends JDialog implements Printable {
private static final long serialVersionUID=20110208L;
private PrinterJob printer=PrinterJob.getPrinterJob();
private PageFormat pf=new PageFormat();
private double scale=1;
private URL imgURL=this.getClass().getResource("shiki.jpg");
private Image img=Toolkit.getDefaultToolkit().getImage(imgURL);
private PreviewCanvas previewCanvas=null;
private JPanel buttonPane=null;
public PrintPreview() {
init();
}
private void init() {
Container container=this.getContentPane();
this.setTitle("打印预览");
this.setResizable(false);
container.add(getPreviewCanvas(), BorderLayout.CENTER);
container.add(getButtonPane(), BorderLayout.SOUTH);
this.pack();
this.setLocationRelativeTo(null);
this.setVisible(true);
this.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
}
private PreviewCanvas getPreviewCanvas() {
if (previewCanvas==null) {
previewCanvas=new PreviewCanvas();
}
return previewCanvas;
}
private JPanel getButtonPane() {
if (buttonPane==null) {
buttonPane=new JPanel(new FlowLayout(FlowLayout.CENTER,50,10));
JButton setUpButton=new JButton("页面设置");
setUpButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
pf=printer.pageDialog(pf);
previewCanvas.repaint();
}
});
buttonPane.add(setUpButton);
JButton printButton=new JButton("开始打印");
printButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
try {
printer.print();
} catch (Exception err) {
err.printStackTrace();
}
}
});
buttonPane.add(printButton);
}
return buttonPane;
}
public int print(Graphics graphics,PageFormat pageFormat,int pageIndex) {
double imageableX=pageFormat.getImageableX();
double imageableY=pageFormat.getImageableY();
int imgWidth=img.getWidth(this);
int imgHeight=img.getHeight(this);
graphics.drawImage(img, (int)(imageableX*scale), (int)(imageableY*scale), (int)(imgWidth*scale), (int)(imgHeight*scale), this);
return Printable.PAGE_EXISTS;
}
private class PreviewCanvas extends Canvas {
private static final long serialVersionUID=20110208L;
public PreviewCanvas() {
this.setPreferredSize(new Dimension(595,389));
}
public void paint(Graphics g) {
Graphics2D g2=(Graphics2D)g;
g2.translate(10, 10);
double width=pf.getWidth();
double height=pf.getHeight();
double imageableX=(int)(pf.getImageableX()-1);
double imageableY=(int)(pf.getImageableY()-1);
double imageableWidth=(int)(pf.getImageableWidth()+2);
double imageableHeight=(int)(pf.getImageableHeight()+2);
if (width>575 || height>374) {
double scaleWidth=(double)575/width;
double scaleHeight=(double)374/height;
scale=scaleWidth<scaleHeight?scaleWidth:scaleHeight;
width=width*scale;
height=height*scale;
imageableX=imageableX*scale;
imageableY=imageableY*scale;
imageableWidth=imageableWidth*scale;
imageableHeight=imageableHeight*scale;
}
g2.drawRect(0, 0, (int)width, (int)height);
float[] dash={
5f,
5f
};
g2.setStroke(new BasicStroke(1f,BasicStroke.CAP_ROUND,BasicStroke.JOIN_ROUND,10f,dash,0f));
g2.drawRect((int)imageableX, (int)imageableY, (int)imageableWidth, (int)imageableHeight);
PrintPreview.this.print(g2, pf, 0);
}
}
public static void main(String[] args) {
new PrintPreview();
}
}

Answer 1

swing中绘图一般都不用canvas了，可以在JComponent或者JPanel的paintComponent函数里绘制

Answer 2

哦哦，换成JPanel就可以了，原来如此
感谢

Answer 3

OK，测试成功代码如下：
import java.io.*;
import java.net.*;
import java.awt.*;
import java.awt.event.*;
import java.awt.print.*;
import javax.swing.*;public class PrintPreview extends JDialog implements Printable {
private static final long serialVersionUID = 20110208L;
private PrinterJob printer = PrinterJob.getPrinterJob();
private PageFormat pf = new PageFormat();
private double scale = 1;
private URL imgURL = this.getClass().getResource("shiki.jpg");
private Image img = Toolkit.getDefaultToolkit().getImage(imgURL);
private PreviewCanvas previewCanvas = null;
private JPanel buttonPane = null; public PrintPreview() {
init();
} private void init() {
Container container = this.getContentPane();
this.setTitle("打印预览");
this.setResizable(false);
container.add(getPreviewCanvas(), BorderLayout.CENTER);
container.add(getButtonPane(), BorderLayout.SOUTH);
this.pack();
this.setLocationRelativeTo(null);
this.setVisible(true);
this.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
} private PreviewCanvas getPreviewCanvas() {
if (previewCanvas == null) {
previewCanvas = new PreviewCanvas();
}
return previewCanvas;
} private JPanel getButtonPane() {
if (buttonPane == null) {
buttonPane = new JPanel(new FlowLayout(FlowLayout.CENTER, 50, 10));
JButton setUpButton = new JButton("页面设置");
setUpButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
pf = printer.pageDialog(pf);
previewCanvas.repaint();
}
});
buttonPane.add(setUpButton);
JButton printButton = new JButton("开始打印");
printButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
scale = 1;
printer.setJobName(new File(imgURL.getFile()).getName());
printer.setPrintable(PrintPreview.this);
try {
printer.print();
} catch (Exception err) {
err.printStackTrace();
}
}
});
buttonPane.add(printButton);
}
return buttonPane;
} public int print(Graphics graphics, PageFormat pageFormat, int pageIndex) {
double imageableX = pageFormat.getImageableX();
double imageableY = pageFormat.getImageableY();
int imgWidth = img.getWidth(this);
int imgHeight = img.getHeight(this);
graphics.drawImage(img, (int) (imageableX * scale),
(int) (imageableY * scale), (int) (imgWidth * scale),
(int) (imgHeight * scale), this);
if (pageIndex == 0) {
return Printable.PAGE_EXISTS;
} else {
return Printable.NO_SUCH_PAGE;
}
} private class PreviewCanvas extends JPanel {
private static final long serialVersionUID = 20110208L; public PreviewCanvas() {
this.setPreferredSize(new Dimension(595, 389));
} public void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g;
g2.translate(10, 10);
double width = pf.getWidth();
double height = pf.getHeight();
double imageableX = pf.getImageableX();
double imageableY = pf.getImageableY();
double imageableWidth = pf.getImageableWidth();
double imageableHeight = pf.getImageableHeight();
if (width > 575 || height > 374) {
double scaleWidth = (double) 575 / width;
double scaleHeight = (double) 374 / height;
scale = scaleWidth < scaleHeight ? scaleWidth : scaleHeight;
width = width * scale;
height = height * scale;
imageableX = imageableX * scale;
imageableY = imageableY * scale;
imageableWidth = imageableWidth * scale;
imageableHeight = imageableHeight * scale;
}
g2.drawRect(0, 0, (int) width, (int) height);
float[] dash = { 5f, 5f };
g2.setStroke(new BasicStroke(1f, BasicStroke.CAP_ROUND,
BasicStroke.JOIN_ROUND, 10f, dash, 0f));
g2.drawRect((int) (imageableX - 1), (int) (imageableY - 1),
(int) (imageableWidth + 2), (int) (imageableHeight + 2));
PrintPreview.this.print(g2, pf, 0);
}
} public static void main(String[] args) {
new PrintPreview();
}
}