如何在按钮处理程序中引用我的 JLabel 消息？

Question

基本上！我需要使用 jtextfields 更改最初设置为红色的消息的颜色，所有代码都已完成，除了更改颜色的位，因为我不知道如何引用消息。我知道它需要执行@overide 操作，但它说它无法识别“消息”是什么，我试过 message.setForeground(new Color(a, b, c));但是，是的，任何关于在这里做什么的帮助都会很棒，谢谢。

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;



public class CE203_2016_Ex1 extends JFrame {

    JTextField tred, tgreen, tblue;

    public CE203_2016_Ex1() {

        JPanel panel1 = new JPanel();       //creates panels for the boxes that will hold the rgb values
        JPanel panel2 = new JPanel();

        tred = new JTextField("Red", 10);
        tgreen = new JTextField("Green", 10);             //creates boxes for rgb values
        tblue = new JTextField("Blue", 10);

        panel1.add(tred);
        panel1.add(tgreen);                            //adding jtextfields to panels
        panel1.add(tblue);

        add(panel1, BorderLayout.SOUTH); //adding panels to frame
        add(panel2, BorderLayout.CENTER);

        JLabel message = new JLabel("hello");  //text
        message.setForeground(new Color(255, 0, 0));     //original text set to red

        JButton goButton = new JButton("Change");       //adds button to change colour
        panel1.add(goButton);
        panel2.add(message);
        goButton.addActionListener(new ButtonHandler(this));
    }

    class ButtonHandler implements ActionListener {

        private CE203_2016_Ex1 theApp;

        public ButtonHandler(CE203_2016_Ex1 theApp) {
            this.theApp = theApp;
        }

        @Override
        public void actionPerformed(ActionEvent e) {
            int a = Integer.parseInt(theApp.tred.getText());
            int b = Integer.parseInt(theApp.tgreen.getText());
            int c = Integer.parseInt(theApp.tblue.getText());


        }
    }

    public static void main(String[] args) {
        JFrame app = new CE203_2016_Ex1();
        app.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        app.setSize(700, 700);
        app.setVisible(true);
    }
}

Answer 1

您需要在您的应用中公开消息标签。这意味着您必须使 JLabel 消息成为您应用程序的一个字段，然后添加一个 getter 来检索它。这样，任何可以访问您的应用的东西也可以访问消息标签。

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;



public class CE203_2016_Ex1 extends JFrame {

    JTextField tred, tgreen, tblue;
    JLabel message;

    public CE203_2016_Ex1() {

        JPanel panel1 = new JPanel();       //creates panels for the boxes that will hold the rgb values
        JPanel panel2 = new JPanel();

        tred = new JTextField("Red", 10);
        tgreen = new JTextField("Green", 10);             //creates boxes for rgb values
        tblue = new JTextField("Blue", 10);

        panel1.add(tred);
        panel1.add(tgreen);                            //adding jtextfields to panels
        panel1.add(tblue);

        add(panel1, BorderLayout.SOUTH); //adding panels to frame
        add(panel2, BorderLayout.CENTER);

        message = new JLabel("hello");  //text
        message.setForeground(new Color(255, 0, 0));     //original text set to red

        JButton goButton = new JButton("Change");       //adds button to change colour
        panel1.add(goButton);
        panel2.add(message);
        goButton.addActionListener(new ButtonHandler(this));
    }

    public JLabel getMessageLabel() {
        return message;
    }

    class ButtonHandler implements ActionListener {

        private CE203_2016_Ex1 theApp;

        public ButtonHandler(CE203_2016_Ex1 theApp) {
            this.theApp = theApp;
        }

        @Override
        public void actionPerformed(ActionEvent e) {
            int a = Integer.parseInt(theApp.tred.getText());
            int b = Integer.parseInt(theApp.tgreen.getText());
            int c = Integer.parseInt(theApp.tblue.getText());
            theApp.getMesssageLabel().setForground(new Color(a, b, c));
        }
    }

    public static void main(String[] args) {
        JFrame app = new CE203_2016_Ex1();
        app.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        app.setSize(700, 700);
        app.setVisible(true);
    }
}

重要的部分是：

JTextField tred, tgreen, tblue;

// Added field message for later use
JLabel message;

public CE203_2016_Ex1() {

.

// Enables you to get the message label from your app later on
public JLabel getMessageLabel() {
    return message;
}

class ButtonHandler implements ActionListener {

.

int c = Integer.parseInt(theApp.tblue.getText());
// Gets the message label from your App and sets its foreground color
theApp.getMesssageLabel().setForground(new Color(a, b, c));

Answer 2

您正试图从其scope 外部访问变量message，因为您在构造函数中声明了JLabel，它只能由构造函数访问。所以你想在构造函数之外声明 JLabel，就像你对 JTextFields 所做的一样，我也建议将此应用程序设为 private。