从另一个类更改变量值

编程问答 2022-06-08

问题描述

我想做这样的事情。

主班 

import javax.swing.JFrame;
import javax.swing.JPanel;
import java.awt.Color;
import javax.swing.JButton;

public class test 
{

 public static JFrame frame;
 public static JPanel panel;    
 public static JButton settings;
 public static int red = 10;
 public static int green = 100;
 public static int blue  = 10;
 
 public static void main( String[] args )
 {
    
  frame = new JFrame();
  frame.setSize(  100,100 );
    
  panel = new JPanel();
  panel.setBackground( new Color( red,green,blue) );
  frame.add(  panel );
  
  settings = new JButton( "settings" );
  panel.add( settings );
  settings.addActionListener( new settingsctionListener() );
  
  frame.setVisible( true );
    
 }

}

另一个班级 

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class settingsctionListener implements ActionListener
{

 @Override
 public void actionPerformed( ActionEvent e )
 {

  test.red = 100;
  test.green = 255;
  test.blue = 255;
  
 }

}

不知道该怎么做。

另一个类应该将变量值更改为红色，绿色和蓝色，以更改整个主题。

有一个方法panel.setBackground（...），但这只会更改面板颜色。喜欢更改整个主题的变量。

解决方法

  • 更新静态变量red，green和blue时，面板和其他元素不会自动更新。它们需要使用各自的“设置”方法分别进行更新。
  • 您需要为其他UI元素添加代码。我只看到JPanel，这是updateTheme中唯一更新的，但是您可能需要添加其他setter调用。
  • 对于样式（不正确）：以大写字母开头的类。
import javax.swing.JFrame;
import javax.swing.JPanel;
import java.awt.Color;
import javax.swing.JButton;

public class EntryPoint {
    public static JFrame frame;
    public static JPanel panel;
    public static JButton settings;
    public static int red = 10;
    public static int green = 100;
    public static int blue  = 10;

    public static void updateTheme(int r,int g,int b) {
        panel.setBackground( new Color(r,g,b) );

        // Update any other UI elements (panels etc).
        // Update the static variables in case they're needed for some reason
        red = r;
        green = g;
        blue = b;
    }
    public static void main( String[] args )
    {

        frame = new JFrame();
        frame.setSize(  100,100 );

        panel = new JPanel();
        panel.setBackground( new Color( red,green,blue) );
        frame.add(  panel );

        settings = new JButton( "settings" );
        panel.add( settings );
        settings.addActionListener( new SettingsActionListener() );

        frame.setVisible( true );

    }

}

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class SettingsActionListener implements ActionListener
{
    // Do not need Override if using ActionListener trait
    public void actionPerformed( ActionEvent e )
    {
        // invoke the static updateTheme method
        EntryPoint.updateTheme(100,255,255);
        System.out.println("Settings updated");
    }
}
,

在找到最终解决方案之前，我们应该对您的代码进行一些整理。特别是

  • 不要从不使用静态变量（样式不好-它不是面向对象的）
  • 使您的起始类继承自JFrame

考虑了这一点之后，您可以采用四种方法来实现ActionListener。 Swing开发中的一种常见方法是使用匿名类。然后它将如下所示：

class SwingTest1 extends JFrame {
    
    final JPanel panel;
    final JButton settings;

    int red = 10;
    int green = 100;
    int blue = 10;

    private SwingTest1() {
        panel = new JPanel();
        panel.setBackground(new Color(red,blue));
        add(panel);

        settings = new JButton("settings");
        panel.add(settings);

        // anonymous ActionListener class
        settings.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                red = 100;
                green = 255;
                blue = 255;
                panel.setBackground(new Color(red,blue));
            }
        });
    }

    public static void main(String[] args) {
        SwingTest1 frame = new SwingTest1();
        frame.setSize(100,100);
        frame.setVisible(true);
    }

}

或者您也可以使您的类也实现ActionListener：

class SwingTest2 extends JFrame implements ActionListener {
    
    final JPanel panel;
    final JButton settings;
    
    int red = 10;
    int green = 100;
    int blue = 10;

    private SwingTest2() {
        panel = new JPanel();
        panel.setBackground(new Color(red,blue));
        add(panel);

        settings = new JButton("settings");
        panel.add(settings);

        // ActionListener as self-reference
        settings.addActionListener(this);
    }
    
    @Override
    public void actionPerformed(ActionEvent e) {
        this.red = 100;
        this.green = 255;
        this.blue = 255;

        panel.setBackground(new Color(red,blue));
    }

    public static void main(String[] args) {
        SwingTest2 frame = new SwingTest2();
        frame.setSize(100,100);
        frame.setVisible(true);
    }

}

如果您真的想拥有两个类，请对框架进行反向引用：

class SwingTest3 extends JFrame {

    final JPanel panel;
    final JButton settings;
    
    int red = 10;
    int green = 100;
    int blue = 10;

    private SwingTest3() {
        panel = new JPanel();
        panel.setBackground(new Color(100,100,10));
        add(panel);

        settings = new JButton("settings");
        panel.add(settings);

        // ActionListener with back reference
        settings.addActionListener(new SettingsListener(this));
    }
    
    public void setColor(int red,int green,int blue) {
        this.red = red;
        this.green = green;
        this.blue = blue;

        panel.setBackground(new Color(red,blue));
    }

    public static void main(String[] args) {
        SwingTest3 frame = new SwingTest3();
        frame.setSize(100,100);
        frame.setVisible(true);
    }

}

和Listener类：

class SettingsListener implements ActionListener {

    final SwingTest3 frame;

    public SettingsListener(SwingTest3 frame) {
        super();
        this.frame = frame;
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        frame.setColor(100,255);
    }
}

从Java 8开始，您还可以将Lamda表达式用作ActionListener。这使您的代码更紧凑，但对于初学者来说可能更难阅读：

class SwingTest4 extends JFrame {
    
    final JPanel panel;
    final JButton settings;

    private SwingTest4() {
        panel = new JPanel();
        panel.setBackground(new Color(100,10));
        add(panel);

        settings = new JButton("settings");
        panel.add(settings);

        // Lambda style ActionListener
        settings.addActionListener(e -> panel.setBackground(new Color(100,255)));
    }

    public static void main(String[] args) {
        SwingTest4 frame = new SwingTest4();
        frame.setSize(100,100);
        frame.setVisible(true);
    }

}

现在由您决定最喜欢哪种解决方案。

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