Java remove listener from button after 3 clicks

问题

So I want to remove a listener from a button after the button has been pressed 3 times. So far I have this

class Q5 
{
JFrame frame;
JButton button;
int clickCount = 0;

public static void main (String[] args)
{
    Q5 example = new Q5();
    example.go();
}

public void go()
{
    frame = new JFrame();

    button = new JButton ("Should I do it");
    button.addActionListener(new ButtonPressListener());
    button.addActionListener(new AngelListener());
    button.addActionListener(new DevilListener());
    button.addActionListener(new ConfusedListener());



    frame.getContentPane().add(BorderLayout.CENTER, button);
    frame.setVisible(true);
    frame.setSize(400,150);
    // set frame properties here
}

class ButtonPressListener implements ActionListener 
{
    public void actionPerformed(ActionEvent event) 
    {
        clickCount++;
    }
}

class AngelListener implements ActionListener 
{
    public void actionPerformed(ActionEvent event) 
    {
        System.out.println("Don't do it, you might regret it!");
    }
}

class DevilListener implements ActionListener 
{
    public void actionPerformed(ActionEvent event) 
    {
        System.out.println("Go on, do it!");
    }
}

class ConfusedListener implements ActionListener   
{
    public void actionPerformed(ActionEvent event) 
    {
        if(clickCount > 3)
        {
            for(ConfusedListener conf : button.getActionListeners())
            {
                button.removeActionListener(conf);
            }
        }
        else
            System.out.println("I don't know!");
    }
}

The way I read online was do a for loop, as I tried above, however I get a type mismatch. Most of the examples I could find were about removing all of the listeners, however I only want to remove the ConfusedListener from the button. Other than the for loop above, I don't have any ideas of how to do it.

回答1:

The getActionListeners() method returns all the listeners of the button. And they're not all instances of ConfusedListener. The only sure thing we know is that they're instances of ActionListener. That's why your code doesn't compile.

Now, why would you need a loop to remove a given listener? You simply need to remove the ConfusedListener that is being invoked. So you just need

public void actionPerformed(ActionEvent event) 
{
    if(clickCount > 3)
    {
        button.removeActionListener(this);
    }
    else
        System.out.println("I don't know!");
}

回答2:

You could try:

if(clickCount > 3)
    {
        for(ActionListener listener : button.getActionListeners())
        {
            if (listener instanceOf ConfusedListener) {
                button.removeActionListener(conf);
            }
        }
    }
    else
        System.out.println("I don't know!");

You could also save the instance of the ConfusedListener when adding it and remove it via

button.removeActionListener(confusedListenerInstance);

回答3:

Just store an instance of the listener itself and use it to remove the correct listener:

final ConfusedListener confusedListener = new ConfusedListener();
button.addActionListener(confusedListener);
button.removeActionListener(confusedListener);

Of if you are removing the listener from inside a method of ConfusedListener itself just pass this:

button.removeActionListener(this);

来源：https://stackoverflow.com/questions/20122762/java-remove-listener-from-button-after-3-clicks

标签

java

swing

button

action

listener