当用户未同时选择PDF＆＃39; S时，我想禁用我的mergeButton。
我该怎么做呢？我尝试做一个while循环来检查file1和file2是否为null但是循环没有终止。
package pdfMerge;
import java.awt.BorderLayout;
import java.awt.GridLayout;
import java.awt.event.ActionListener;
import java.io.File;
import java.io.IOException;
import javax.swing.JButton;
import javax.swing.JFileChooser;
import javax.swing.JFrame;
import javax.swing.JPanel;
import org.apache.pdfbox.exceptions.COSVisitorException;
import org.apache.pdfbox.pdmodel.PDDocument;
import org.apache.pdfbox.util.PDFMergerUtility;
import java.awt.event.*;
public class pdfMerger extends JFrame {
private static final String ActionEvent = null;
private JButton choose1, choose2, mergeButton;
private JFileChooser fileChooser1, fileChooser2;
private JPanel contentsPane;
private int returnValue1, returnValue2;
private File file1, file2;
private String fileName1, fileName2;
private boolean valid;
public pdfMerger(){
super("PDF Merger");
setLayout(new BorderLayout());
setSize(500, 500);
setDefaultCloseOperation(EXIT_ON_CLOSE);
addComponents();
addAction();
setVisible(true);
}
public void addComponents(){
contentsPane = new JPanel(new GridLayout(0, 3));
add(contentsPane, BorderLayout.SOUTH);
choose1 = new JButton("Choose 1st pdf");
choose2 = new JButton("Choose 2nd pdf");
mergeButton = new JButton("Merge");
fileChooser1 = new JFileChooser();
fileChooser2 = new JFileChooser();
contentsPane.add(choose1);
contentsPane.add(choose2);
contentsPane.add(mergeButton);
}
public void addAction(){
choose1.addActionListener(
new ActionListener(){
public void actionPerformed(ActionEvent event){
if (event.getSource() == choose1){
returnValue1 = fileChooser1.showOpenDialog(null);
if (returnValue1 == JFileChooser.APPROVE_OPTION){
file1 = fileChooser1.getSelectedFile();
fileName1 = file1.toString();
fileName1 = fileName1.replace("\\", "\\\\");
System.out.println(fileName1);
}
}
}
}
);
choose2.addActionListener(
new ActionListener(){
public void actionPerformed(ActionEvent event){
if (event.getSource() == choose2){
returnValue2 = fileChooser2.showOpenDialog(null);
if (returnValue2 == JFileChooser.APPROVE_OPTION){
file2 = fileChooser2.getSelectedFile();
fileName2 = file2.toString();
fileName2 = fileName2.replace("\\", "\\\\");
System.out.println(fileName2);
}
}
}
}
);
mergeButton.addActionListener(
new ActionListener(){
public void actionPerformed(ActionEvent event){
PDFMergerUtility ut = new PDFMergerUtility();
ut.addSource(fileName1);
ut.addSource(fileName2);
ut.setDestinationFileName("C:\\Users\\Shaheedul\\Desktop\\MergedPDF.pdf");
try {
ut.mergeDocuments();
} catch (Exception error){
System.out.println("Something went wrong!");
}
}
}
);
}
}
答案 0 :(得分：4)
简单：将mergeButton或其Action禁用设置为以：
开头mergeButton.setEnabled(false);
然后在文件的动作侦听器中选择按钮，如果选择了2个文件，则设置mergeButton。
e.g。请注意标记为// !!，
// !! class names should begin with upper case letter
public class PdfMerger extends JFrame {
// ...
private JButton choose1, choose2, mergeButton;
// ...
public PdfMerger() {
super("PDF Merger");
setLayout(new BorderLayout());
setSize(500, 500); // advise against this
setDefaultCloseOperation(EXIT_ON_CLOSE);
addComponents();
addAction();
setVisible(true);
// !!
mergeButton.setEnabled(false);
}
// ...
public void addAction() {
choose1.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent event) {
if (event.getSource() == choose1) {
returnValue1 = fileChooser1.showOpenDialog(null);
if (returnValue1 == JFileChooser.APPROVE_OPTION) {
file1 = fileChooser1.getSelectedFile();
fileName1 = file1.toString();
fileName1 = fileName1.replace("\\", "\\\\");
System.out.println(fileName1);
// !! added
mergeButton.setEnabled(bothFilesChosen());
}
}
}
});
choose2.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent event) {
if (event.getSource() == choose2) {
returnValue2 = fileChooser2.showOpenDialog(null);
if (returnValue2 == JFileChooser.APPROVE_OPTION) {
file2 = fileChooser2.getSelectedFile();
fileName2 = file2.toString();
fileName2 = fileName2.replace("\\", "\\\\");
System.out.println(fileName2);
// !! added
mergeButton.setEnabled(bothFilesChosen());
}
}
}
});
// ....
}
// !!
private boolean bothFilesChosen() {
return (file1 != null && file1.exists() && file2 != null && file2.exists());
}
}
答案 1 :(得分：4)
好吧，当你有一个选择按钮时，你应该在Swing组件中显示所选文件，这样用户就可以看到选择了哪个文件。如果您没有显示值，用户如何知道他们点击了两个按钮？此外，如果禁用“合并”按钮，用户如何知道单击哪个“选择”按钮以启用合并按钮？
因此，在这种情况下，您可以使用不可编辑的文本字段。然后，您可以为每个文本字段添加DocumentListener。每当在任一字段中更改文本时，您都会检查是否应启用/禁用“合并”按钮。
以下是此方法的一个示例：
import java.awt.*;
import java.awt.event.*;
import java.util.List;
import java.util.ArrayList;
import javax.swing.*;
import javax.swing.event.*;
public class DataEntered implements DocumentListener
{
private JButton button;
private List<JTextField> textFields = new ArrayList<JTextField>();
public DataEntered(JButton button)
{
this.button = button;
}
public void addTextField(JTextField textField)
{
textFields.add( textField );
textField.getDocument().addDocumentListener( this );
}
public boolean isDataEntered()
{
for (JTextField textField : textFields)
{
if (textField.getText().trim().length() == 0)
return false;
}
return true;
}
@Override
public void insertUpdate(DocumentEvent e)
{
checkData();
}
@Override
public void removeUpdate(DocumentEvent e)
{
checkData();
}
@Override
public void changedUpdate(DocumentEvent e) {}
private void checkData()
{
button.setEnabled( isDataEntered() );
}
private static void createAndShowUI()
{
JButton submit = new JButton( "Submit" );
submit.setEnabled( false );
JTextField textField1 = new JTextField(10);
JTextField textField2 = new JTextField(10);
DataEntered de = new DataEntered( submit );
de.addTextField( textField1 );
de.addTextField( textField2 );
JFrame frame = new JFrame("SSCCE");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(textField1, BorderLayout.WEST);
frame.add(textField2, BorderLayout.EAST);
frame.add(submit, BorderLayout.SOUTH);
frame.pack();
frame.setLocationByPlatform( true );
frame.setVisible( true );
}
public static void main(String[] args)
{
EventQueue.invokeLater(new Runnable()
{
public void run()
{
createAndShowUI();
}
});
}
}