I am trying to attach an UndoableEditListener to a JTextPane or JTextArea that queues up edits into an UndoManager.
textPane.getDocument().addUndoableEditListener(new UndoableEditListener() {
#Override
public void undoableEditHappened(UndoableEditEvent event) {
undoQueue.addEdit(event.getEdit());
}
});
But undoableEditHappened is never called when I type "aaa" in the text window.
Thinking it's Java's fault, not mine, I crack AbstractDocument.class open with Eclipse debugger to watch the event trigger. It has a private listeners array. AbstractDocument stores all its listeners in odd indices in the listeners array, with the listeners' type Class<>'s in the even indices.
protected void fireUndoableEditUpdate(UndoableEditEvent e) {
// Guaranteed to return a non-null array
Object[] listeners = listenerList.getListenerList();
// Process the listeners last to first, notifying
// those that are interested in this event
for (int i = listeners.length - 2; i >= 0; i -= 2) {
if (listeners[i] == UndoableEditListener.class) {
// Lazily create the event:
// if (e == null)
// e = new ListSelectionEvent(this, firstIndex, lastIndex);
((UndoableEditListener) listeners[i + 1]).undoableEditHappened(e);
}
}
}
See the line if (listeners[i] == UndoableEditListener.class)? When I add the undo change listener, the debugger shows listeners containing my listener, along with UndoableEditListener.class in the index before it. But, when the debugger comes to that if-statement, all the even indices in the array listeners show as DocumentListener.class in the debugger. Consequently, the if-statement is always false and the listener never called.
What the heck? Is this a Java 8 bug? Or am I missing a step the examples forgot to mention?
The problem was in the JTextPane. I was overriding its setText method to force it to call read, the alternative to setText that normalizes all kinds of newline while remembering them. But JTextPane.read appears to not trigger an UndoableEditEvent on the document.
If I leave setText alone, then UndoManager.undo works.
Related
I have 62 check boxes on 2 different panels.
30 of them on each panel are for selecting PC names while 1 on each selects all.
So on each of those 60 that are just selecting items I have this code:
private void HP04ActionPerformed(java.awt.event.ActionEvent evt) {
// TODO add your handling code here:
setComponent(HP04, blrS,all_blr);
HP04 is the name of a checkbox for one of the PCs, blrS is the name of an int that counts how many checkboxes are selected(there is another int for the boxes on the other panel), all_blr is the name of the checkbox that selects all on the blr panel.
This is the method I used:
public void setComponent(javax.swing.JCheckBox component, int room,javax.swing.JCheckBox all)
{
System.out.println("Inside Component: "+component.isSelected()); //testing to see if the method is actually being called
if (component.isSelected()){ //if checkbox is checked
room++; //records how many boxes are checked
if (room == 30)
{
all.setSelected(true);//autochecks "all" check box if all PCs are selected
}
if (!messagearea.getText().equals(""))
{
sendb.setEnabled(true);//if any boxes are checked and the message area is populated, enable the button
}
}
else
{
room--;//records how many boxes are checked
all.setSelected(false);//unchecks the "all" check box if not all of them are checked
if (room == 0)
{
sendb.setEnabled(false);//disables button if no PCs are selected to be messaged
}
}
System.out.println(room); //testing int updates based on UI changes
}
Now the problem is room is only fetching the value of whatever variable is put in that parameter and then room itself is being modified. So in the example setComponent(HP04, blrS,all_blr); blrS is never changed.
I know the code inside the method works, it worked before I decided to cut down on code by using a method, as before I had the code inside the method in the actionperformed for every checkbox before hand... Like this:
private void HP04ActionPerformed(java.awt.event.ActionEvent evt) {
if (HP04.isSelected()){
blrS++;
if (blrS == 30)
{
all_blr.setSelected(true);
}
if (!messagearea.getText().equals(""))
{
sendb.setEnabled(true);
}
}
else
{
blrS--;
all_blr.setSelected(false);
if (blrS == 0)
{
sendb.setEnabled(false);
}
}
System.out.println(blrS);
}
It's just understanding how parameters and methods works that is tripping me up.
It feels obvious that what I'm doing shouldn't work, room is a variable inside the method... But how do I change that?
Solution found:
"Why not return room from the method, and assign it to the variable when you call it? blrS = setComponent(HP04, blrS, all_blr);"
– Rob Spoor (in the comments to this post)
I've been having a problem with my program that has been driving me crazy and I cannot understand why this is happening. I have a GUI that when the "Add" button is pressed, a new system listing appears (Which is a class called SystemPanel that extends JPanel and cotains system details, which is created and then put into the Frame's main panel.)
To put it shortly, when I try to add a new SystemPanel, it does not appear for whatever reason. I have code using JSch that connects to the system and verifies whether its processes are online or not, but the line of code that does this is after the creation of the SystemPanel. It is only after the code for testing the processes of the system are executed that the SystemPanel becomes visible, and I can't understand why this is the case. Here is the code for adding a new SystemPanel:
public void actionPerformed(ActionEvent e) {
//If the "Add" button is pressed
if (e.getActionCommand() == "Add") {
PopupWindow popup = new PopupWindow(this);
popup.setVisible(true);
String[] results = popup.getResults();
if (results[0] != null && results[1] != null && results[2] != null && results[3] != null && results[4] != null) {
SystemPanel newSystem = new SystemPanel(this, results[0], results[1], results[2], results[3], results[4]);
systemsPanel.add(newSystem);
revalidate();
systemsList.add(newSystem);
System.out.println("Did the stuff");
boolean[] status = SystemChecker.checkOnline(results[0], results[1], results[2], results[3]);
}
}
}
The PopupWindow is a custom JDialog that allows the user to enter the required information which is returned in a String array and is used to create a new SystemPanel. The checkOnline function grabs the user's inputs and uses them to connect to the system and determine whether the processes are working or not, and returns the results into a boolean array, true for working, false for not.
What's even weirder is that I have another part of my program that reads from an .ini file to obtain existing systems and then creates SystemPanels based on the data that it reads. Through this method, the SystemPanels are added the way I want and work perfectly for some reason, even though the code for adding the panels is hardly any different. Code:
for (int i = 0; i < systems.size(); i++) {
SystemPanel newSystem = new SystemPanel(this, systems.get(i)[0], systems.get(i)[1], systems.get(i)[2], systems.get(i)[3], systems.get(i)[4]);
systemsPanel.add(newSystem);
revalidate();
systemsList.add(newSystem);
}
for (int i = 0; i < lineNum; i++) {
boolean[] status = SystemChecker.checkOnline(systems.get(i)[0], systems.get(i)[1], systems.get(i)[2], systems.get(i)[3]);
systemsList.get(i).updateIcons(status);
}
This code grabs the details from the file and then makes the SystemPanels based on those details. Here, all of the SystemPanels are added and show up before the connection is tested, which is what I want to happen when I add one normally.
Why is it that the SystemPanel doesn't appear until the connection is tested, even though the code for displaying the SystemPanel is executed before the connection test? Any help would be greatly appreciated, thanks.
Try it of the current event queue handling, on which actionPerformed is done.
public void actionPerformed(ActionEvent e) {
EventQueue.invokeLater(() -> { ... your code here ... });
}
Also you cannot add the same component to two parents, every component object has a single parent (container).
(Java 8 notation)
I'm a beginner in Java programming & I am making an application requiring an object to move around a grid filled with squares.
The object should only move one square at a time and if the user wants to move into another square, they must press the key again. My move method is the following:
public void move() {
x += dx;
y += dy;
}
I am using the KeyListener interface to implement the keyPressed, keyTyped and keyReleased methods and I have conditions like the one in the fragment below inside KeyPressed
//KeyPressed
int c = e.getKeyCode();
if (c == KeyEvent.VK_UP) {
player.setDy(-5);
}
This allows the object to move freely. However, it will clearly continue to move as long as the UP arrow is pressed.
Is there any way to have to object move up by say -5 once and then stop even if the key is still pressed?
I am unsure whether I need to change my move method or the KeyListener methods to do this.
I hope that I have been clear enough as to what I'm asking and I'd highly appreciate any pointers.
first of all : you should use Synchronization if you call class-methods from within listeners like keyPressed or keyReleased - thats because your listener-method can be called from multiple threads so your class-method (player.setDy()) can (and will) be called in parallel - you will need to make sure that each call to setDy happens before the next one.
Also : keyTyped is much better in many cases : https://stackoverflow.com/a/7071810/351861
An example could look like this:
public void keyTyped(KeyEvent arg0) {
if(arg0.getKeyCode() == KeyEvent.VK_UP)
{
synchronized(player)
{
player.setDy(-5);
}
}
}
this will call setDy sequentially and reliably. Now all you need to do is to make sure that setDy works as intended, hence sets the position only once
easiest would be to add a boolean to indicate, that a moving key is pressed
class member : boolean movingKeyPressed = false
in key pressed :
if (movingKeyPressed) {
return;
} else {
// do stuff
movingKeyPressed = true;
}
in key released method :
movingKeyPressed = false;
this is my first question, so help me please. I try to save the value of the method getStelectedRow in a type int variable(row) to next can use the method getValueAt(row,column). My problem is the value of my variable, it's -1, and this means the row is not selected, but I'm selecting a row.
The error is the next:
Exception in thread "AWT-EventQueue-0" java.lang.ArrayIndexOutOfBoundsException: -1
If need more details just say me. Thanks.
EDIT:
My code is:
int row = jTablePersonal.getSelectedRow();
String query = "select * from table where id ='"+jTablePersonal.getValueAt(row,0)+"'";
The error point to the variable "row" when I call the method "getValueAt(row,0)"
Seems like a newbie problem. Given your explanation
"My problem is the value of my variable, it's -1, and this means the row is not selected, but I'm selecting a row."
You do not have this code inside a listener, you have like it your constructor or something. You want to have the code inside the listener. Something like
button.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e) {
int row = table.getSelectedRow();
if (row != -1) {
// do something
}
}
});
If you are using the Netbeans GUI Builder tool, you can
From the design view right click the button and go to Events -> Action -> actionPerformed
Go to you source view and you should see some auto-generated code like
jButton1ActionPerformed(java.awt.event.ActionEvent evt) {
}
Write the code there.
You should also take some time to read How to write Event Listeners. GUI Programs are event driven, so you need to learn how to respond to these events by registering listeners
the problem is about getSelectedRow();
getSelectedRow is only work if table is current selected
my suggestion is , make temp variable to get last selectedrow to prevent error ,like
if(table.getSelectedRow()!=-1)
{
int lastselected=table.getSelectedRow();
}
I need to remove all items from the combo box
int itemCount = combo.getItemCount();
for(int i = 0; i < itemCount; i++){
combo.removeItemAt(0);
}
This code will remove all items except the last one. It gives a NullPointerException.
How to fix that?
The code in the question would normally work. However, it looks like a threading issue. Another thread may be messing with the items.
However, I sugeest you should better use the removeAllItems(); method:
combo.removeAllItems();
How about JComboBox.removeAllItems()?
You can use
this.combo.removeAllItems();
to remove all the items in JComboBox.
In second line:
combo.removeItemAt(0);
I think instead of 0 it should be i.
do it in reverse order as:
for(int i=combo.getItemCount()-1;i>=0;i--){
combo.removeItemAt(i);
}
But in my case combo.removeAllItems() works fine
use .removeAllItems() methods to remove all items from combo box.
The assumption that it is related to another thread is not always true. It can be the thread itself causing the issue.
This exception may happen because an event is triggered when a combo item is removed and in this event handling method you still refer to combobox items.
For example when you delete somewhere (other than in actionPeformed()) in your code the last item from a combo box with combo.removeItemAt(0) or removeAllItems() then still the event actionPerformed will be fired/executed. But very often the actionPerformed() method contains code to react on user actions (user clicked somewhere on the combobox). So, when the last item has been deleted there is no more item in the combobox and any reference to an item or index in actionPerformed() will cause an exception.
The solution to this is to move the code from actionPerformed() to e.g. mouseClicked() or another event handler depending on what you want to do.
removeAllItems() it does remove all things but after the add data to the combo box it will not show there ,the nullPointException will shows
Use this to remove all the elements from the combo box :
DefaultComboBoxModel model = (DefaultComboBoxModel) ComboBox.getModel();
model.removeAllElements();
Usually it happens because you have an event associated JComboBox. It is solved if you have control item in the JComboBox to act, for example:
jComboBoxExample.addActionListener (new ActionListener () {
public void actionPerformed (ActionEvent e) {
do_run ();
}
});
public void do_run() {
int n=jComboBoxPerfilDocumentos.getItemCount(); <--THIS IS THE SOLUTION
if (n> 0) {
String x = jComboBoxPerfilDocumentos.getSelectedItem (). ToString ();
}
}