只有在java中不再可见窗口后才读取值

Question

也许我只是不知道在哪里看或不完全理解线程如何工作,但我有两个不同的JFrame(J1,J2).J1是主JFrame,它有一个选择J2的下拉菜单.当这个J2变得可见时,我需要J1等待J2的foobar值变为-1以外的值.我试图用几种不同的方式给这只猫上皮而没有成功.

我现在正在尝试...

// located in J1
J2 otherFrame = new J2();
....

private synchronized void getNum() {
    try {
        while (otherFrame.returnNum() == -1) wait();
    }
    catch (Exception e) {}
    Long myResult = otherFrame.returnNum();
    ...
}



// located in J2
public synchronized Long returnNum() {
    try {
        while (someNum == -1) wait();
    }
    catch (Exception e) {}
    notify();
    return someNum;
}

我确信这看起来很愚蠢,但是我需要J1等到J2有一个赋值给someNum的值.用户单击"提交"时将分配该值.它没有做好这项工作.我在这里做错了什么(更重要的是),如果这是一个线程的事情,我的线程概念在哪里失败？

Answer 1

解决方案不是将JFrame用于第二个窗口,而是使用模态对话框,例如模态JDialog.这正是为此类型的顶级窗口构建的.

这个问题是为什么人们应该避免编写扩展JFrame的Swing类的另一个原因,因为这样做会将编码器描绘成一个角落并限制他们的选择.更好的是创建扩展或构建用于创建JPanel的类,从那时起JPanel可以放在JFrame或模态JDialog中,如果需要,或者放在另一个JPanel中,或者在CardLayout中交换,或者......

请注意,除了一些差异之外,使用JDialog与JFrame非常相似.你应该在对话框中传入一个对调用窗口的引用(这里是你的第一个JFrame),你应该使用使对话框模态化的构造函数,但API可以帮助你完成所有这些.

当您使模态窗口可见时,调用代码中的代码流将停止,并且在JDialog不再可见之前不会恢复.那时你可以查询JDialog的组件的状态,并在调用代码中使用它.

例如:

import java.awt.Window;
import java.awt.Dialog.ModalityType;
import java.awt.event.ActionEvent;

import javax.swing.*;

public class DialogEg {
    private static void createAndShowGui() {

        // create JFrame for application
        JFrame frame = new JFrame("Dialog Eg");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add(new MainPanel());
        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
    }

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

@SuppressWarnings("serial")
class MainPanel extends JPanel {
    private JTextField valueField = new JTextField(5);

    public MainPanel() {
        valueField.setFocusable(false); // so user can't interact with it

        add(new JLabel("Value:"));
        add(valueField);
        add(new JButton(new GetValueAction("Get Value")));
    }

    private class GetValueAction extends AbstractAction {
        private SecondPanel secondPanel = new SecondPanel();

        public GetValueAction(String name) {
            super(name);
            int mnemonic = (int) name.charAt(0);
            putValue(MNEMONIC_KEY, mnemonic);
        }

        @Override
        public void actionPerformed(ActionEvent e) {
            // get JPanel's top level window
            Window win = SwingUtilities.getWindowAncestor(MainPanel.this);

            // create jdialog that is modal
            JDialog dialog = new JDialog(win, "Get Value", ModalityType.APPLICATION_MODAL);
            dialog.add(secondPanel);

            // so the submit button will be activated when enter pressed:
            dialog.getRootPane().setDefaultButton(secondPanel.getSubmitButton());
            dialog.pack();
            dialog.setLocationRelativeTo(win);
            dialog.setVisible(true); // **** code flow stops here

            // and resumes here once dialog is no longer visible
            int value = secondPanel.getSpinnerValue();
            valueField.setText("" + value);
        }
    }
}

@SuppressWarnings("serial")
class SecondPanel extends JPanel {
    private SpinnerModel spinModel = new SpinnerNumberModel(-1, -1, 100, 1);
    private JSpinner spinner = new JSpinner(spinModel);
    private JButton submitButton = new JButton(new SubmitAction("Submit"));

    public SecondPanel() {
        add(spinner);
        add(submitButton);
    }

    public int getSpinnerValue() {
        return (Integer) spinner.getValue();
    }

    public JButton getSubmitButton() {
        return submitButton;
    }

    private class SubmitAction extends AbstractAction {
        public SubmitAction(String name) {
            super(name);
            int mnemonic = (int) name.charAt(0);
            putValue(MNEMONIC_KEY, mnemonic);
        }

        @Override
        public void actionPerformed(ActionEvent e) {
            int value = getSpinnerValue();

            // get JPanel's top level window
            Window win = SwingUtilities.getWindowAncestor(SecondPanel.this);
            if (value < 0) {
                String msg = "Submitted value must cannot be negative. Please try again";
                JOptionPane.showMessageDialog(win, msg, "Invalid Entry", JOptionPane.ERROR_MESSAGE);
                spinner.requestFocusInWindow(); // bring focus back to spinner
            } else {
                spinner.requestFocusInWindow();
                win.dispose();  // get rid of dialog
            }
        }
    }
}