Thread: How to set a button event trigger?

Hi.
I have created a modal dialog box thus:

	JDialog dialog = new  JDialog();
	dialog.setModal(true);
	dialog.setSize(400, 150);
 
	dialog.setTitle("Input dialog");
 
	Container pane = dialog.getContentPane();
pane.setLayout(null);
 
 
	JLabel l1 = new JLabel("simtime(min)");
	pane.add(l1);
	l1.setBounds(10, 10, 100, 10);
 
		JTextField  tf = new JTextField("");
	pane.add( tf);
	tf.setBounds(110,10, 40, 15);
 
	JLabel l2 = new JLabel("interval(sec)") ;
pane.add(l2);
	l2.setBounds(10, 50, 100, 10);
 
	JTextField  tf2 = new JTextField("");
	pane.add( tf2);
	tf2.setBounds(110,50, 40, 15);
	dialog.setVisible(true);	
 
	JButton button = new JButton("OK");
pane.add(button);
button.setBounds(120,120,40,20);
 
 
		int simTime = Integer.parseInt( tf.getText() );;
		int interval = Integer.parseInt( tf2.getText() );

But nothing happens when I click on the "OK" button. Why?and what should I do?

Thanks in advance

At what point in your code do you tell the button what to do when it is clicked?

Originally Posted by Cornix

At what point in your code do you tell the button what to do when it is clicked?

Before the last two lines.

--- Update ---

Originally Posted by Norm

You need an action listener. See the tutorial: How to Write an Action Listener (The Java™ Tutorials > Creating a GUI With JFC/Swing > Writing Event Listeners)

But this way, there is no way to distinguish between different events for one component, isn't it?

No you dont.
This is "before the last 2 lines":

JButton button = new JButton("OK");
pane.add(button);
button.setBounds(120,120,40,20);

And you dont tell the button anything here. Just because it displays "OK" as its label does not mean that it knows what to do when its clicked.

Originally Posted by Cornix

No you dont.
This is "before the last 2 lines":

JButton button = new JButton("OK");
pane.add(button);
button.setBounds(120,120,40,20);

And you dont tell the button anything here. Just because it displays "OK" as its label does not mean that it knows what to do when its clicked.

No.I meant I want the last two lines onward be executed then. there is processing code not shown here.
Again, the last two lines are:

int simTime = Integer.parseInt( tf.getText() );;
int interval = Integer.parseInt( tf2.getText() );

And where do you tell the button that it is supposed to execute these lines?

Originally Posted by Cornix

And where do you tell the button that it is supposed to execute these lines?

It is the topic of this topic

Originally Posted by hooshdar3

It is the topic of this topic

Well, this was your question:

But nothing happens when I click on the "OK" button. Why?

So the answer is pretty simple: Nothing happens because you never told the button what to do when it is being clicked.

As far as I know there are 2 ways to define the behavior of a button:
1) You give it an "Action"-Object. This action object will define the behavior when clicked.

2) You add an ActionListener to the button. When clicked, the button will notify all ActionListeners that have been registered to it.

An example in code:

JButton btn = new Button();
btn.addActionListener(new ActionListener() {
    public void actionPerformed(ActionEvent e) {
         // do stuff
    }
});

Originally Posted by Cornix

Well, this was your question:

So the answer is pretty simple: Nothing happens because you never told the button what to do when it is being clicked.

As far as I know there are 2 ways to define the behavior of a button:
1) You give it an "Action"-Object. This action object will define the behavior when clicked.

2) You add an ActionListener to the button. When clicked, the button will notify all ActionListeners that have been registered to it.

An example in code:

JButton btn = new Button();
btn.addActionListener(new ActionListener() {
    public void actionPerformed(ActionEvent e) {
         // do stuff
    }
});

Do I have to put the code inside a function?

N.B:Should the second line be:
btn.addActionListener( new ActionListener() )?

Perhaps you should read up on anonymous classes.

Originally Posted by hooshdar3

Do I have to put the code inside a function?

I asked because then the TextFields will not be known in the function actionPerformed()

Make it known. If you dont want to make it a private member variable you can also declare it as "final".

Originally Posted by Cornix

Make it known. If you dont want to make it a private member variable you can also declare it as "final".

The end-user is supposed to enter numbers in the text-fields. Doesn't Final make them unchangable? What about private?

Originally Posted by Norm

final means the variable's value can't be changed. The contents of the object can be changed.

What do you mean?
I declare them as e.g:

public static final JTextField tf = new JTextField("")

outside any function? then what happens when the user chabges their content? Will

tf.getText()

return the string representation of the number entered?

no, dont use static, and dont make it a member variable either. you just declare them is final within your method. The same method you have been using already.
This means that you can not use the same variable to create a new JTextField, but all of the variables inside the JTextField class can change same as before.

For example:

public void initGUI() {
	final JTextField txtF = new JTextField();
 
	JButton btn = new JButton();
	btn.addActionListener(new ActionListener {
		String content = txtF.getText();
		System.out.println(content);
	});
}

Hi.
I set an action listener for my button but nothing happens when the button is clicked.Why?
Here is my code:

public class sysinfoHooshi implements ActionListener{
    static JTextField  tf = new JTextField("");
    static JTextField  tf2 = new JTextField("");
 
	public static void simulate()throws Exception{
	JDialog dialog = new  JDialog();
	dialog.setModal(true);
	dialog.setSize(400, 150);
 
	dialog.setTitle("Input dialog");
 
	Container pane = dialog.getContentPane();
        pane.setLayout(null);
 
 
	JLabel l1 = new JLabel("simtime(min)");
	pane.add(l1);
	l1.setBounds(10, 10, 100, 10);
 
 
	pane.add( tf);
	tf.setBounds(110,10, 40, 15);
 
	JLabel l2 = new JLabel("interval(sec)") ;
	pane.add(l2);
	l2.setBounds(10, 50, 100, 10);
 
 
	pane.add( tf2);
	tf2.setBounds(110,50, 40, 15);
 
	JButton button = new JButton("OK");
	pane.add(button);
	button.setBounds(100,100,40,20);
	dialog.setVisible(true);
 
//some code
 
	}//end simulate()
	 public void actionPerformed(ActionEvent e) {tf2.setText("Hello");}
public static void main(String args[]) throws Exception{	
	simulate();
	} // end main
   }// end class

Thanks in advance

You need to tell the button that the class is the action listener.

button.addActionListener(this);

You can read up on Action Listeners here

--- Update ---

Oh, and you can also do away with the 'implements ActionListener' and use anonymous inner classes. They are real nifty.

button.setOnClickListener(new OnClickListener() {
    public void onClick(View v) {
        simulate();
    }
});

Essentially the same topic, the same road being repaved, threads merged.

Originally Posted by ChristopherLowe

You need to tell the button that the class is the action listener.

button.addActionListener(this);

Heh!unbelievable!I haven't done that!

OK, I added that line, and now get the compile error:

non-static variable this cannot be referenced from a static context
button.addActionListener(this);
^
1 error

And this ground has been covered before. Please read the advice you've been given and apply it. If you don't understand it, then continue asking questions. DON'T bail to a new thread where potentially the conversation has to start all over again. If you don't follow the advice given or at least acknowledge it with questions, those trying to help will give up on you as untrainable.

Originally Posted by GregBrannon

And this ground has been covered before. Please read the advice you've been given and apply it. If you don't understand it, then continue asking questions. DON'T bail to a new thread where potentially the conversation has to start all over again. If you don't follow the advice given or at least acknowledge it with questions, those trying to help will give up on you as untrainable.

OK, but I have asked my question already