问题
I have modified code from here for my project. I want to make a editor that have dynamic text area. Each time I press the enter key, a new text area will create. Sorry, I cannot explain more with English.
Please look my code:
import javax.swing.*;
import javax.swing.text.*;
import java.awt.*;
import java.io.*;
import java.awt.event.*;
import java.util.Hashtable;
public class SimpleEditor extends JFrame {
int count = 0;
private Action openAction = new SimpleEditor.OpenAction();
private Action saveAction = new SimpleEditor.SaveAction();
//private JTextComponent textComp;
private JTextComponent[] textComp2;
//private Hashtable actionHash = new Hashtable();
public static void main(String[] args) {
SimpleEditor editor = new SimpleEditor();
editor.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
editor.setVisible(true);
}
// Create an editor.
public SimpleEditor() {
super("Swing Editor");
//textComp = createTextComponent();
coba();
makeActionsPretty();
Container content = getContentPane();
//content.add(textComp, BorderLayout.CENTER);
for (int i = 0; i < count; i++) {
content.add(textComp2[i], BorderLayout.CENTER);
}
content.add(createToolBar(), BorderLayout.NORTH);
setJMenuBar(createMenuBar());
setSize(320, 240);
}
//coba-coba
protected void coba() {
if (count == 0) {
textComp2 = new JTextComponent[1];
count += 1;
} else {
JTextComponent[] texttemp;
texttemp = new JTextComponent[count];
for (int i = 0; i < count; i++) {
texttemp[i] = createTextComponent();
texttemp[i] = textComp2[i];
}
count += 1;
textComp2 = new JTextComponent[count];
for (int i = 0; i < count - 1; i++) {
textComp2[i] = createTextComponent();
textComp2[i] = texttemp[i];
}
}
}
// Create the JTextComponent subclass.
protected JTextComponent createTextComponent() {
JTextArea ta = new JTextArea();
ta.setFont(new Font("Courier New", Font.PLAIN, 12));
ta.setLineWrap(true);
ta.addKeyListener(new java.awt.event.KeyAdapter() {
public void keyPressed(java.awt.event.KeyEvent ev) {
taKeyPressed(ev);
}
});
return ta;
}
private void taKeyPressed(java.awt.event.KeyEvent ev) {
if (ev.getKeyCode() == 13) {
coba();
}
}
// Add icons and friendly names to actions we care about.
protected void makeActionsPretty() {
Action a;
/*a = textComp.getActionMap().get(DefaultEditorKit.cutAction);
a.putValue(Action.SMALL_ICON, new ImageIcon("icons/cut.gif"));
a.putValue(Action.NAME, "Cut");
a = textComp.getActionMap().get(DefaultEditorKit.copyAction);
a.putValue(Action.SMALL_ICON, new ImageIcon("icons/copy.gif"));
a.putValue(Action.NAME, "Copy");
a = textComp.getActionMap().get(DefaultEditorKit.pasteAction);
a.putValue(Action.SMALL_ICON, new ImageIcon("icons/paste.gif"));
a.putValue(Action.NAME, "Paste");
a = textComp.getActionMap().get(DefaultEditorKit.selectAllAction);
a.putValue(Action.NAME, "Select All");*/
for (int i = 0; i < count; i++) {
a = textComp2[i].getActionMap().get(DefaultEditorKit.cutAction);
a.putValue(Action.SMALL_ICON, new ImageIcon("icons/cut.gif"));
a.putValue(Action.NAME, "Cut");
a = textComp2[i].getActionMap().get(DefaultEditorKit.copyAction);
a.putValue(Action.SMALL_ICON, new ImageIcon("icons/copy.gif"));
a.putValue(Action.NAME, "Copy");
a = textComp2[i].getActionMap().get(DefaultEditorKit.pasteAction);
a.putValue(Action.SMALL_ICON, new ImageIcon("icons/paste.gif"));
a.putValue(Action.NAME, "Paste");
a = textComp2[i].getActionMap().get(DefaultEditorKit.selectAllAction);
a.putValue(Action.NAME, "Select All");
}
}
// Create a simple JToolBar with some buttons.
protected JToolBar createToolBar() {
JToolBar bar = new JToolBar();
// Add simple actions for opening & saving.
bar.add(getOpenAction()).setText("");
bar.add(getSaveAction()).setText("");
bar.addSeparator();
// Add cut/copy/paste buttons.
/*bar.add(textComp.getActionMap().get(DefaultEditorKit.cutAction)).setText("");
bar.add(textComp.getActionMap().get(
DefaultEditorKit.copyAction)).setText("");
bar.add(textComp.getActionMap().get(
DefaultEditorKit.pasteAction)).setText("");*/
for (int i = 0; i < count; i++) {
bar.add(textComp2[i].getActionMap().get(DefaultEditorKit.cutAction)).setText("");
bar.add(textComp2[i].getActionMap().get(
DefaultEditorKit.copyAction)).setText("");
bar.add(textComp2[i].getActionMap().get(
DefaultEditorKit.pasteAction)).setText("");
}
return bar;
}
// Create a JMenuBar with file & edit menus.
protected JMenuBar createMenuBar() {
JMenuBar menubar = new JMenuBar();
JMenu file = new JMenu("File");
JMenu edit = new JMenu("Edit");
menubar.add(file);
menubar.add(edit);
file.add(getOpenAction());
file.add(getSaveAction());
file.add(new SimpleEditor.ExitAction());
/* edit.add(textComp.getActionMap().get(DefaultEditorKit.cutAction));
edit.add(textComp.getActionMap().get(DefaultEditorKit.copyAction));
edit.add(textComp.getActionMap().get(DefaultEditorKit.pasteAction));
edit.add(textComp.getActionMap().get(DefaultEditorKit.selectAllAction));*/
for (int i = 0; i < count; i++) {
edit.add(textComp2[i].getActionMap().get(DefaultEditorKit.cutAction));
edit.add(textComp2[i].getActionMap().get(DefaultEditorKit.copyAction));
edit.add(textComp2[i].getActionMap().get(DefaultEditorKit.pasteAction));
edit.add(textComp2[i].getActionMap().get(DefaultEditorKit.selectAllAction));
}
return menubar;
}
// Subclass can override to use a different open action.
protected Action getOpenAction() {
return openAction;
}
// Subclass can override to use a different save action.
protected Action getSaveAction() {
return saveAction;
}
//protected JTextComponent getTextComponent() { return textComp; }
// ********** ACTION INNER CLASSES ********** //
// A very simple exit action
public class ExitAction extends AbstractAction {
public ExitAction() {
super("Exit");
}
public void actionPerformed(ActionEvent ev) {
System.exit(0);
}
}
// An action that opens an existing file
class OpenAction extends AbstractAction {
public OpenAction() {
super("Open", new ImageIcon("icons/open.gif"));
}
// Query user for a filename and attempt to open and read the file into the
// text component.
public void actionPerformed(ActionEvent ev) {
JFileChooser chooser = new JFileChooser();
if (chooser.showOpenDialog(SimpleEditor.this)
!= JFileChooser.APPROVE_OPTION) {
return;
}
File file = chooser.getSelectedFile();
if (file == null) {
return;
}
FileReader reader = null;
try {
reader = new FileReader(file);
//textComp.read(reader, null);
for (int i = 0; i < count; i++) {
textComp2[i].read(reader, null);
}
} catch (IOException ex) {
JOptionPane.showMessageDialog(SimpleEditor.this,
"File Not Found", "ERROR", JOptionPane.ERROR_MESSAGE);
} finally {
if (reader != null) {
try {
reader.close();
} catch (IOException x) {
}
}
}
}
}
// An action that saves the document to a file
class SaveAction extends AbstractAction {
public SaveAction() {
super("Save", new ImageIcon("icons/save.gif"));
}
// Query user for a filename and attempt to open and write the text
// component’s content to the file.
public void actionPerformed(ActionEvent ev) {
JFileChooser chooser = new JFileChooser();
if (chooser.showSaveDialog(SimpleEditor.this)
!= JFileChooser.APPROVE_OPTION) {
return;
}
File file = chooser.getSelectedFile();
if (file == null) {
return;
}
FileWriter writer = null;
try {
writer = new FileWriter(file);
//textComp.write(writer);
for (int i = 0; i < count; i++) {
textComp2[i].write(writer);
}
} catch (IOException ex) {
JOptionPane.showMessageDialog(SimpleEditor.this,
"File Not Saved", "ERROR", JOptionPane.ERROR_MESSAGE);
} finally {
if (writer != null) {
try {
writer.close();
} catch (IOException x) {
}
}
}
}
}
}
But, my code have some error like this:
Exception in thread "main" java.lang.NullPointerException
- at SimpleEditor.makeActionsPretty(SimpleEditor.java:101)
- at SimpleEditor.<init>(SimpleEditor.java:29)
- at SimpleEditor.main(SimpleEditor.java:19)
Can anybody help me as soon as possible?
回答1:
The array JTextComponent[] has different sizes at different times, but an object in the array defaults to null until you change it:
textComp2[i] = new JTextField("Hello");
来源：https://stackoverflow.com/questions/16687812/dynamic-simple-text-editor-java