java 将 ActionListener 添加到 JTextArea 的解决方法
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Workaround for adding ActionListener to JTextArea
提问by mastodon
I have a program that get's input string with file path in one JTextArea and then loads it's content to a second JTextArea. Problem is that when using JTextArea I cannot add an actionListener that will load content in the second JTextArea when leaving this field. How to get around this problem ?
我有一个程序，它在一个 JTextArea 中获取带有文件路径的输入字符串，然后将其内容加载到第二个 JTextArea。问题是，当使用 JTextArea 时，我无法添加一个 actionListener，它会在离开此字段时在第二个 JTextArea 中加载内容。如何解决这个问题？
protected JTextArea inputField, outputField;
public Main(){
super(new BorderLayout());
inputField = new JTextArea(5, 20);
outputField = new JTextArea(2, 20);
//inputField.addActionListener(this);
inputField.setEditable(false);
JScrollPane scroller2 = new JScrollPane(inputField);
JScrollPane scroller1 = new JScrollPane(outputField);
this.add(scroller1, BorderLayout.WEST);
this.add(scroller2, BorderLayout.EAST);
}
public void actionPerformed(ActionEvent evt) {
String text = inputField.getText();
(loading contents of file)
}
回答by I82Much
You do not want an actionListener, you want a FocusListener.
您不需要 actionListener ，而是需要FocusListener。
JTextArea text = ...;
text.addFocusListener(new FocusListener() {
public void focusGained(FocusEvent e) {}
public void focusLost(FocusEvent e) {
// Load your content.
}
});
回答by Andrew Thompson
Or, to flesh out my first comment, try this SSCCE that uses a JButton (& a JEditorPane for the content).
或者，为了充实我的第一条评论，请尝试使用 JButton（和 JEditorPane 作为内容）的这个 SSCCE。
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.border.*;
import java.io.File;
class LoadDocument {
public static void main(String[] args) {
Runnable r = new Runnable() {
public void run() {
final JFrame f = new JFrame();
f.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
JPanel contentPane = new JPanel( new BorderLayout(3,3) );
contentPane.setBorder( new EmptyBorder(5,5,5,5) );
// has convenience methods to load documents..
final JEditorPane content = new JEditorPane();
JScrollPane sp = new JScrollPane(content);
sp.setPreferredSize( new Dimension(400,400) );
contentPane.add( sp, BorderLayout.CENTER );
final JFileChooser jfc = new JFileChooser();
JButton open = new JButton("Open File");
open.addActionListener( new ActionListener(){
public void actionPerformed(ActionEvent ae) {
int result = jfc.showOpenDialog(f);
if (result==JFileChooser.APPROVE_OPTION) {
File file = jfc.getSelectedFile();
try {
content.setPage( file.toURI().toURL() );
} catch(Exception e) {
e.printStackTrace();
JOptionPane.showMessageDialog(
f,
"File load error!",
e.getMessage(),
JOptionPane.ERROR_MESSAGE
);
}
}
}
} );
JToolBar tb = new JToolBar();
tb.add(open);
contentPane.add( tb, BorderLayout.NORTH );
f.setContentPane( contentPane );
f.pack();
f.setLocationByPlatform(true);
f.setVisible(true);
}
};
SwingUtilities.invokeLater(r);
}
}
回答by Enyby
If you need only ActionListener, check this example:
如果您只需要 ActionListener，请查看此示例：
textArea.addFocusListener(new FocusAdapter() {
@Override
public void focusLost(FocusEvent e) {
actionListener.actionPerformed(new ActionEvent(e.getSource(), e.getID(), "focusLost"));
}
});
Its equals:
它等于：
textArea.addActionListener(actionListener);
P. S. actionListener must be final or class field for use in that way.
PS actionListener 必须是 final 或 class 字段才能以这种方式使用。
