只有在JFrame中更改了某些内容时，才能使JButton可单击

I have a JFrame with JTextFields, JComboBoxes and JLabels. I want to make the button "UPDATE" clickable only if something has been changed(fields) in the window.

我有一个JFrame与JTextFields，JComboBoxes和JLabels。我想只在窗口中的某些内容被更改（字段）时才使“UPDATE”按钮可单击。

1 个解决方案

#1

I want to make the button "UPDATE" clickable only if something has been changed(fields) in the window.

我想只在窗口中的某些内容被更改（字段）时才使“UPDATE”按钮可单击。

You'll need to listen for changes in your "fields" (whatever they are supposed to be), and in that listener call setEnabled(true) or setEnabled(false) on your JButton of interest -- or better on its Action, depending on the state of your fields. Why is the Action better? You can have several buttons and JMenuItems share the same Action, and by calling the methods on the Actions, you would disable both at the same time.

您需要监听“字段”中的更改（无论它们应该是什么），并在该侦听器中调用您感兴趣的JButton上的setEnabled（true）或setEnabled（false） - 或者更好地依赖它的Action，具体取决于在你的领域的状态。为什么行动更好？您可以有多个按钮和JMenuItem共享相同的Action，通过调用Actions上的方法，您可以同时禁用它们。

For example, if the fields are JTextFields, then add a DocumentListener to your fields, and based on the state of the fields in the listener, call the method I've noted above.

例如，如果字段是JTextFields，则将DocumentListener添加到字段中，并根据侦听器中字段的状态调用上面提到的方法。

If you need more concrete help, then you'll want to provide us with more concrete information and code.

如果您需要更具体的帮助，那么您需要向我们提供更具体的信息和代码。

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For an example with 5 JTextFields and a JButton, where the JButton is only active if text is present in every JTextField:

有一个包含5个JTextFields和一个JButton的例子，其中JButton仅在每个JTextField中都有文本时才有效：

package pkg;

import java.awt.event.*;

import javax.swing.*;
import javax.swing.event.DocumentEvent;
import javax.swing.event.DocumentListener;

@SuppressWarnings("serial")
public class ButtonActiveTest extends JPanel {
    private static final int FIELD_COUNT = 5;

    private MyAction myAction = new MyAction("My Button"); // The Action
    private JButton myButton = new JButton(myAction);  // the button 
    private JTextField[] textFields = new JTextField[FIELD_COUNT];


    public ButtonActiveTest() {
        myAction.setEnabled(false); // initially disable button's Action

        // create single Doc listener
        MyDocumentListener myDocumentListener = new MyDocumentListener();
        // create jtext fields in a loop
        for (int i = 0; i < textFields.length; i++) {
            textFields[i] = new JTextField(5); // create each text field

            // add document listener to doc
            textFields[i].getDocument().addDocumentListener(myDocumentListener);

            // add to gui
            add(textFields[i]);
        }
        add(myButton);

    }

    private static void createAndShowGui() {
        ButtonActiveTest mainPanel = new ButtonActiveTest();

        JFrame frame = new JFrame("ButtonActiveTest");
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        frame.getContentPane().add(mainPanel);
        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGui();
            }
        });
    }

    private class MyAction extends AbstractAction {
        public MyAction(String name) {
            super(name);
            int mnemonic = (int) name.charAt(0);
            putValue(MNEMONIC_KEY, mnemonic); // to give button an alt-key hotkey
        }

        @Override
        public void actionPerformed(ActionEvent e) {
            JOptionPane.showMessageDialog(ButtonActiveTest.this, "Button Pressed");
        }
    }

    private class MyDocumentListener implements DocumentListener {

        @Override
        public void changedUpdate(DocumentEvent e) {
            checkFields();
        }

        @Override
        public void insertUpdate(DocumentEvent e) {
            checkFields();
        }

        @Override
        public void removeUpdate(DocumentEvent e) {
            checkFields();
        }

        // if any changes to any document (any of the above methods called)
        // check if all JTextfields have text. If so, activate the action
        private void checkFields() {
            boolean allFieldsHaveText = true;
            for (JTextField jTextField : textFields) {
                if (jTextField.getText().trim().isEmpty()) {
                    allFieldsHaveText = false;
                }
            }

            myAction.setEnabled(allFieldsHaveText);
        }

    }
}

---

Showing similar code, but now with a JMenuItem sharing the same Action as the JButton. Note that both the menu item and the button are active/inactive in parallel:

显示类似的代码，但现在JMenuItem与JButton共享相同的Action。请注意，菜单项和按钮并行处于活动/非活动状态：

import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.DocumentEvent;
import javax.swing.event.DocumentListener;

@SuppressWarnings("serial")
public class ButtonActiveTest extends JPanel {
    private static final int FIELD_COUNT = 5;

    private MyAction myAction = new MyAction("Process Data in Fields"); // The Action
    private JButton myButton = new JButton(myAction);  // the button 
    private JTextField[] textFields = new JTextField[FIELD_COUNT];
    private JMenuBar menuBar = new JMenuBar();


    public ButtonActiveTest() {
        myAction.setEnabled(false); // initially disable button's Action

        // create single Doc listener
        MyDocumentListener myDocumentListener = new MyDocumentListener();
        // create jtext fields in a loop
        for (int i = 0; i < textFields.length; i++) {
            textFields[i] = new JTextField(5); // create each text field

            // add document listener to doc
            textFields[i].getDocument().addDocumentListener(myDocumentListener);

            // add to gui
            add(textFields[i]);
        }
        add(myButton);

        // create menu item with our action
        JMenuItem menuItem = new JMenuItem(myAction);
        JMenu menu = new JMenu("Menu");
        menu.setMnemonic(KeyEvent.VK_M);
        menu.add(menuItem);
        menuBar.add(menu);
    }

    public JMenuBar getMenuBar() {
        return menuBar;
    }

    private static void createAndShowGui() {
        ButtonActiveTest mainPanel = new ButtonActiveTest();

        JFrame frame = new JFrame("ButtonActiveTest");
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        frame.getContentPane().add(mainPanel);
        frame.setJMenuBar(mainPanel.getMenuBar());
        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGui();
            }
        });
    }

    private class MyAction extends AbstractAction {
        public MyAction(String name) {
            super(name);
            int mnemonic = (int) name.charAt(0);
            putValue(MNEMONIC_KEY, mnemonic); // to give button an alt-key hotkey
        }

        @Override
        public void actionPerformed(ActionEvent e) {
            JOptionPane.showMessageDialog(ButtonActiveTest.this, "Action Performed!");
        }
    }

    private class MyDocumentListener implements DocumentListener {

        @Override
        public void changedUpdate(DocumentEvent e) {
            checkFields();
        }

        @Override
        public void insertUpdate(DocumentEvent e) {
            checkFields();
        }

        @Override
        public void removeUpdate(DocumentEvent e) {
            checkFields();
        }

        // if any changes to any document (any of the above methods called)
        // check if all JTextfields have text. If so, activate the action
        private void checkFields() {
            boolean allFieldsHaveText = true;
            for (JTextField jTextField : textFields) {
                if (jTextField.getText().trim().isEmpty()) {
                    allFieldsHaveText = false;
                }
            }

            myAction.setEnabled(allFieldsHaveText);
        }

    }
}