Here's an abrevated version of what my code looks like:
public class ColorFactory extends JFrame {
public ColorFactory(){
buildTopPanel();
}
public void buildTopPanel(){
JPanel topPanel = new JPanel();
this.add(topPanel, BorderLayout.NORTH);
}
}
As you can see I have a method that makes a new JPanel object when called. How can I access that particular JPanel object from another class? I have a button listener class that I want to change the color of the JPanel from outside the ColorFactory class. This code is right after the ColorFactory class.
public class ButtonListener implements ActionListener{
public void actionPerformed(ActionEvent e) {
//Change JPanel color here.
}
}
Would it be better just to instantiate JPanel in the ColorFactory constructor and then just access it through there?
For starters, you need to make the JPanel a field in ColorFactory, so references to it don't disappear when you exit buildTopPanel(). Once you've saved a reference to it, then you have a couple of choices. From the design standpoint, the bad choice is to expose it, e.g.:
JPanel getTopPanel(){
return topPanel;
}
The better choice is to have your action listener send a message to ColorFactory that says "respondToButton(Color newColor)", and have ColorFactory decide to change topPanel's color... e.g.:
public void respondToButton(Color newColor){
topPanel.setBackground(newColor);
}
You are facing a design issue; in general, this type of situations require more investigation to understand how to end up with a clean and maintainable design.
However, For the specific problem you are reporting, I would:
Create a constructor of ButtonListener that receives a parameter (i.e. the ColorFactory) which could access the information you need, so that you can initialize a field in ButtonListener itself
Create a method changeColor in the ColorFactory. This method actually applies the color change
In the ButtonListener, invoke changeColor on the field, i.e. the reference to the ColorFactory
You should make the JPanel a field of the class like this:
public class ColorFactory extends JFrame {
JPanel topPanel;
public ColorFactory(){
buildTopPanel();
}
public void buildTopPanel(){
topPanel = new JPanel();
this.add(topPanel, BorderLayout.NORTH);
}
public void changeColor(Color color) {
//color changing code here
}
}
now You can get the JPanel from another class.
All you have to do now, is get the ColorFactory into your Button listener:
public class ButtonListener implements ActionListener{
ColorFactory colorFactory;
public ButtonListener(ColorFactory colorFactory) {
this.colorFactory = colorFactory;
}
public void actionPerformed(ActionEvent e) {
colorFactory.changeColor(/* color here */);
}
}
Related
I am struggling with the ActionListener in Java in a parent class, I tried a bunch of possible solutions but could not get it work. This here also did not help:
Java actionlistener actionPerformed in different class
The problem is as follows:
Class2 extends Class1, I have a button in Class2. As soon as the button in Class2 is pressed, Class1 should be notified through action listener and perform the event.
I'm struggling to let Class1 know that the event has happened. It looked pretty simple to me, but nevertheless I'm struggling.
Your help will be much apprechiated, thank you!
Parent Class
package test;
//imports removed for better visibility
public class ParentClass extends JPanel implements ActionListener{
JFrame frame;
public void createParentGui() {
frame = new JFrame("Frame");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
final JPanel mainCard = new JPanel(new CardLayout(20, 20));
ChildClass card1 = new ChildClass();
mainCard.add(card1);
frame.add(mainCard, BorderLayout.CENTER);
frame.pack();
frame.setVisible(true);
}
#Override
public void actionPerformed(ActionEvent e)
{
System.out.println("Button pressed, action!");
}
}
Child Class
package test;
//imports removed for better visibility
public class ChildClass extends ParentClass {
ActionListener listener = null; //this is probably not right, how to do
//with a local variable when passing it to the parent class?
public Child() {
createGui();
}
private void createGui() {
final JButton b = new JButton("press me");
b.addActionListener(listener);
add(b);
}
}
ChildClass has all of the fields and methods that ParentClass does (in addition to its own unique fields and methods). This is how inheritance works.
So, since ParentClass is an ActionListener, that means that ChildClass is too. More specifically, ChildClass has inherited the public void actionPerformed(ActionEvent e) method of ParentClass.
Therefore, change b.addActionListener(listener); to b.addActionListener(this). (you can also remove the listener field of ChildClass)
The new code will pass "this" ChildClass object to b, which will then call actionPerformed(ActionEvent e) whenever the button is pressed. And since any ChildClass object has the actionPerformed(ActionEvent e) of ParentClass, that means that ParentClass#actionPerformed(ActionEvent) will be called (as you intended).
First off this is a homework assignment so explanations and pointers are preferred over flat solutions. We are learning swing and are practicing separate class ActionListeners (bonus question, why would you use a separate class over an inner class, it seems like inner class is simpler and less error prone without losing any real abilities). The problems I have been running into are passing the Frame as a parameter so that the separate class can access the tools it needs, and then using the separate class to actually change the display. The project is supposed to work something like a slideshow, having a timer as a default switch, but also implementing buttons to move manually.
import javax.swing.*;
import java.awt.BorderLayout;
import java.awt.Image;
import java.awt.event.*;
import java.io.File;
public class SliderFrame extends JFrame{
public SliderFrame(){
File file1 = new File("images"); //change as necessary
File file = new File("images\\CMU");
File[] paths;
paths = file.listFiles();
//file1
ImageIcon left = new ImageIcon("backward.png");
ImageIcon right = new ImageIcon("forward.png");
JButton btnLeft = new JButton(left);
btnLeft.addActionListener(new MyActionListener(this));
JButton btnRight = new JButton(right);
btnRight.addActionListener(new MyActionListener(this));
JTextField jtfTitle = new JTextField("Welcome to CMU!");
JLabel jlbMain = new JLabel();
new Timer(2000, new MyActionListener(this)).start();
JPanel panel = new JPanel();
panel.setLayout(new BorderLayout());
panel.add("PAGE_START", jtfTitle);
panel.add("Center", jlbMain);
panel.add("LINE_START", btnLeft);
panel.add("LINE_END", btnRight);
add(panel);
setTitle("CPS240 SlideShow");
setLocationRelativeTo(null);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
pack();
setVisible(true);
}
public static void main(String[] args) {
JFrame frame = new SliderFrame();
btnRight.addActionListener(new MyActionListener(frame));
}
}
And then my ActionListener Class
import java.awt.event.*;
import javax.swing.*;
//does it need to extend SliderFrame? Originally I thought it would help with some of my errors
public class MyActionListener extends SliderFrame implements ActionListener {
JFrame frame;
public MyActionListener(JFrame frame) {
this.frame = frame;
}
#Override
public void actionPerformed(ActionEvent e) {
if(e.getSource() instanceof Timer){
//here's where I need to be able to change the 'main' label in the frame
} else if(e.getSource() == btnRight){
//trying to figure out if the left or right button was pushed
} else{
}
}
}
I'm not sure if the source of my errors lie in how I set up the format to start with or if I'm just not getting something. Any help or opinions would be greatly appreciated.
bonus question, why would you use a separate class over an inner class, it seems like inner class is simpler and less error prone without losing any real abilities
Initially, you had no choice, as you couldn't have inner classes, but, there may be occasions where the functionality is common and can easily be repeated, for example, an "Open File" action, which is manged by a toolbar button, menu item and keyboard short cut...
First your ActionListener does not need to extend from SliderFrame, but instead, probably wants a reference to an instance of SliderFrame...
This
public class MyActionListener extends SliderFrame implements ActionListener {
Should probably be more like
public class MyActionListener implements ActionListener {
Instead of passing a reference of JFrame, you will want to pass a reference of SliderFrame. Having said that, I have no idea where btnRight is, but I'm pretty sure it shouldn't be maintained within the main method, but within the SliderFrame itself...
public class SliderFrame extends JFrame{
public SliderFrame(){
//...
btnRight.addActionListener(new MyActionListener(this));
You ActionListener should also expect an instance of SliderFrame
public class MyActionListener extends SliderFrame implements ActionListener {
private SliderFrame frame;
public MyActionListener(SliderFrame frame) {
This allows your ActionListener to make use of functionality that is defined by the SliderFrame, which won't be available from an instance of JFrame
Next, you want to provide functionality in your SliderFrame which can be used to update the state of the slide show...
public class SliderFrame extends JFrame{
//...
public void nextSlide() {
//...
}
public void previousSlide() {
//...
}
Then when your ActionListener is triggered, you just call the appropriate methods on SliderFrame
public class NextSlideActionListener extends SliderFrame implements ActionListener {
//...
#Override
public void actionPerformed(ActionEvent e) {
frame.nextSlide();
}
}
(ps- the above example can be used by the Timer and "next" button, because the functionality is the same for both)
I have one jFrame and its have one jTextbox and a button. Another jFrame have a single jLabel. I want to bring out the text written in first frame's textbox to second frame's jLabel when button is pressed. And as i have searched about this than i got some unreliable answers. But as per my knowledge it could be done by creating another static class or by calling this reference.
It is a question of "what" you want to achieve that will drive the "how"...
For example...
You could maintain a reference to the second frame within the first frame and when the button is clicked, tell the second frame that a change has occurred...
public class FirstFrame extends JFrame {
// Reference to the second frame...
// You will need to ensure that this is assigned correctly...
private SecondFrame secondFrame;
// The text field...
private JTextField textField;
/*...*/
// The action handler for the button...
public class ButtonActionHandler implements ActionListener {
public void actionPerformed(ActionEvent evt) {
secondFrame.setLabelText(textField.getText());
}
}
}
The problem with this is it exposes the SecondFrame to the first, allowing it to do nasty things to it, like remove all the components for example.
A better solution would be to provide a series of interfaces that would allow the two classes to talk with each other...
public interface TextWrangler {
public void addActionListener(ActionListener listener);
public void removeActionListener(ActionListener listener);
public String getText();
}
public class FirstFrame extends JFrame implements TextWrangler {
private JButton textButton;
private JTextField textField;
/*...*/
public void addActionListener(ActionListener listener) {
textButton.addActionListener(listener);
}
public void removeActionListener(ActionListener listener) {
textButton.removeActionListener(listener);
}
public String getText() {
return textField.getText();
}
}
public class SecondFrame extends JFrame {
private JLabel textLabel;
private JTextField textField;
private TextWrangler textWrangler;
public SecondFrame(TextWrangler wrangler) {
textWrangler = wrangler;
wrangler.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent evt) {
textLabel.setText(textWrangler.getText());
}
});
/*...*/
}
}
This basically restricts what the SecondFrame can actually gain access to. While it can be argued that the ActionListener in the SecondFrame could use the ActionEvent source to find out more information, by it's nature, it would be an unreliable mechanism, as the interface makes no mention of how it should be implemented...
This is a basic example of the Observer Pattern
The simplest way to pass the data between two JFrames is to create a public method.
By this you can create the public method in your class where you want to get the data and call this method directly with an object of second class.
And also if you want to call it without creating an extra object than just make you method static and call is directly with the class name.
for further details
visit this link
Say, you have a subclass of JFrame, and use it to create your own custom JFrame. In this class (we'll call it mainFrame), we create a reference to another custom JFrame class (we'll call this one sidePanel).
In sidePanel, you have different buttons, radio buttons,..
My question is, is there a way to notify mainFrame the user presses on a button?
I've created a (untested) example of what I mean:
class mainFrame extends JFrame {
public mainFrame() {
super("main frame");
//...........
sidePanel panel = new sidePanel();
//...........
}
public static void main(String[] args) {
mainFrame mainF = new mainFrame();
//.........
}
}
And the sidePanel class:
class sidePanel extends JFrame {
public sidePanel() {
super("sidePanel frame");
//...........
JButton button1 = new JButton();
button1.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e)
{
//Notify mainFrame somehow button is pressed
}});
//...........
}
}
To notify mainFrame of an event, the SidePanel instance (really bad name for a Frame) must have a reference to mainFrame. Pass mainFrame as an argument of the SidePanel constructor, and callback mainFrame from the actionPerformed method in SidePanel:
SidePanel panel = new SidePanel(this);
and in SidePanel:
public void actionPerformed(ActionEvent e) {
mainFrame.buttonHasBeenClicked();
...
}
This tightly couples both classes though. A way to decouple them is to make the SidePanel object accept listeners for custom events, and to fire such an event when the button is clicked. The mainFrame would construct the SidePanel instance, and add itself (or an inner anonymous class instance) as a listener to the sidePanel.
See this page for an example.
I have simple Swing GUI with main window JFrame and its main panel derive from JPanel. The panel has some buttons that can be clicked and generate events.
I want these events affect data stored in JFrame because it is my main application - it has some queues for thread, open streams and so on.
So how do I make my button in panel invoke callbacks in its parent frame? What is best practice of this for Java/Swing?
To invoke methods in the parent frame you need a reference to the parent frame. So your JPanel's constructor can be declared like this:
public MyPanel(MyFrame frame){
super();
this.frame = frame;
//the rest of your code
}
And in the JFrame you invoke this constructor like this:
panel = new MyPanel(this);//this refers to your JFrame
In the event handlers attached to your buttons you now have access to the frame and can invoke the various methods as needed.
button1.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e){
//do some stuff
frame.someMethod();//invoke method on frame
//do more stuff
}
});
Have a look on this tutorial for using SwingWorker.
Use addActionListener method on desired buttons specifying the class implementing ActionListener.
ActionListenerClass actionListenerObject = new actionListenerClass();
JButton b = new JButton("Button");
b.addActionListener(actionListenerObject);
public class ActionListenerClass implements ActionListener(){
//or better : actionListenerClass extends AbstractAction
public void actionPerformed(ActionEvent e) {
}
}
EDIT:
Yes, I know this. But the action
listener I want to be in parent JFrame
class - this is the problem
then extends JFrame class making the new derived class implementing the desired interface.
You can implement the ActionListener in your class that has the JFrame (or extends it):
class MyPanelClass {
public MyPanelClass(ActionListener al)
{
//...
JButton myButton = new JButton("Button");
myButton.addActionListener(al);
//...
}
}
class MainClass extends JFrame implements ActionListener {
public void someMethod() {
MyPanelClass mpc = new MyPanelClass(this);
}
#Override
public void ActionPerformed(ActionEvent ev) {
// your implementation
}
}