java - 在另一个类中更改 Jbutton 的值后使用 PaintComponent 进行绘图

Question

我有一个名为 ControlsPanel 的类。如果我按下此类中的 JButton (Start)， boolean 值 (isPressed) 的值将更改为 true。在另一个类(CashRegistersPanel)中，我想绘制一个图像，但只有前一个类中的 boolean 值为true。当然，这个 boolean 值一开始就是 false，所以它不会绘制任何东西。

这是我的两个类(class):

    public ControlsPanel(final ParametersPanel panel) {         
        start       = new JButton("Start");
        stop        = new JButton("Stop");          
        start.setFont(new Font("Arial", Font.BOLD, 14));
        stop.setFont(new Font("Arial", Font.BOLD, 14));         
        this.setLayout(null);
        this.setBackground(new Color(199,202,255));         
        this.add(start);
        this.add(stop);         
        start.setBounds(10, 10, 280, 30);
        stop.setBounds(10, 50, 280, 30);            
        stop.setEnabled(false);    
        start.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent arg0) {

                if (start.getText().equals("Start")) {
                    start.setText("Pause");
                    stop.setEnabled(true);
                    startIsPressed = true;
                }                   
            }
        });    

    public boolean StartisPressed() {
        return startIsPressed;
    }

}

还有

public class CashRegistersPanel extends JPanel{

    private Image img;
    private int amount;
    private ParametersPanel parametersPanel;
    private ControlsPanel controlsPanel;
    private boolean startIsPressed;

    public CashRegistersPanel(ParametersPanel parametersPanel, ControlsPanel controlPanel) {            
        this.parametersPanel = parametersPanel;
        this.controlsPanel = controlPanel;          
        startIsPressed = controlsPanel.StartisPressed();            
        this.setBackground(new Color(237,237,237));
        this.setLayout(null);           
        CashRegister cashRegister = new CashRegister();
        img = cashRegister.getImg();            
        amount = parametersPanel.getAmountOfRegisters();            
    }

    //Painting CashRegisters
    public void paintComponent(Graphics g) {

        if(startIsPressed) {        
        super.paintComponent(g);
        for (int i = 1; i <= amount; i++) {
            g.drawImage(img, 30, i*50, this);
        }
        }
    }
}

Answer 1

您的问题可以简单地归结为:当更改发生时，如何向一个类通知另一个类的状态更改。这是事件驱动的 GUI 程序(以及其他程序类型)中的常见问题，也是开发观察者或监听器类型设计模式的全部原因。所以我的建议就是，您以某种方式使用监听器设计模式。这可以通过多种方式实现，包括:

• 允许一个类将 ActionListener 附加到第一个类的 JButton
• 让观察者类向更改状态的类(带有 JButton 的类)添加某种类型的监听器
或者我最喜欢的:将 boolean 值完全从 View 类中取出并放入模型类中，并让任何 View 希望收到通知以向模型注册监听器，并根据需要对模型状态的更改使用react。我经常使用后者，通常使用 PropertyChangeListener 来实现此目的。

<小时/>

因此模型类可能类似于:

class Model {
   public static final String START = "start"; // for the property change name
   private SwingPropertyChangeSupport pcSupport = new SwingPropertyChangeSupport(
         this);
   private boolean start = false;

   public boolean isStart() {
      return start;
   }

   public void setStart(boolean start) {
      // to set up our PropertyChangeEvent
      boolean oldValue = this.start;
      boolean newValue = start;
      this.start = start;

      // notify our listeners that the start property has changed
      pcSupport.firePropertyChange(START, oldValue, newValue);
   }

   // allow listeners to be added and removed
   public void addPropertyChangeListener(PropertyChangeListener listener) {
      pcSupport.addPropertyChangeListener(listener);
   }

   public void removePropertyChangeListener(PropertyChangeListener listener) {
      pcSupport.removePropertyChangeListener(listener);
   }
}

<小时/>

编辑例如，下面是一个 M-V 或 Model-View 简单示例程序:

import java.awt.Color;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.beans.PropertyChangeListener;

import javax.swing.*;
import javax.swing.event.SwingPropertyChangeSupport;

public class VerySimpleModelEg {
   private static void createAndShowGui() {
      Model model = new Model();
      ButtonView view1 = new ButtonView();
      DrawingView view2 = new DrawingView();

      view1.setModel(model);
      view2.setModel(model);

      JPanel mainPanel = new JPanel(new GridLayout(1, 0));
      mainPanel.add(view1);
      mainPanel.add(view2);

      JFrame frame = new JFrame("Very Simple Model Example");
      frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
      frame.getContentPane().add(mainPanel);
      frame.pack();
      frame.setLocationRelativeTo(null);
      frame.setVisible(true);
   }

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

class Model {
   public static final String START = "start"; // for the property change name
   private SwingPropertyChangeSupport pcSupport = new SwingPropertyChangeSupport(
         this);
   private boolean start = false;

   public boolean isStart() {
      return start;
   }

   public void setStart(boolean start) {
      // to set up our PropertyChangeEvent
      boolean oldValue = this.start;
      boolean newValue = start;
      this.start = start;

      // notify our listeners that the start property has changed
      pcSupport.firePropertyChange(START, oldValue, newValue);
   }

   // allow listeners to be added and removed
   public void addPropertyChangeListener(PropertyChangeListener listener) {
      pcSupport.addPropertyChangeListener(listener);
   }

   public void removePropertyChangeListener(PropertyChangeListener listener) {
      pcSupport.removePropertyChangeListener(listener);
   }
}

@SuppressWarnings("serial")
class ButtonView extends JPanel {
   public static final String PRESS_TO_START = "Press To Start";
   public static final String PRESS_TO_STOP = "Press To Stop";
   private Model model;
   private Action buttonAction = new ButtonAction();

   public ButtonView() {
      add(new JButton(buttonAction));
      setBorder(BorderFactory.createTitledBorder("Button View"));
   }

   public void setModel(Model model) {
      this.model = model;
      model.addPropertyChangeListener(new BtnViewModelListener());
   }

   private class ButtonAction extends AbstractAction {
      public ButtonAction() {
         super(PRESS_TO_START);
      }

      @Override
      public void actionPerformed(ActionEvent e) {

         // if the button is pressed, toggle the state 
         // of the model's start property
         model.setStart(!model.isStart()); 
      }
   }

   private class BtnViewModelListener implements PropertyChangeListener {
      public void propertyChange(java.beans.PropertyChangeEvent evt) {

         // if the model's start property changes
         if (Model.START.equals(evt.getPropertyName())) {
            // change the Action's name property
            // which will change the JButton's text too!
            String text = model.isStart() ? PRESS_TO_STOP : PRESS_TO_START;
            buttonAction.putValue(Action.NAME, text);
         }
      };
   }


}

@SuppressWarnings("serial")
class DrawingView extends JPanel {
   private static final Color START_COLOR = Color.red;
   private static final Color STOP_COLOR  = Color.blue;
   private Model model;

   public DrawingView() {
      setBorder(BorderFactory.createTitledBorder("Drawing View"));
      setBackground(STOP_COLOR);
   }

   public void setModel(Model model) {
      this.model = model;
      model.addPropertyChangeListener(new DrawingViewModelListener());
   }


   private class DrawingViewModelListener implements PropertyChangeListener {
      public void propertyChange(java.beans.PropertyChangeEvent evt) {

         // if the model's start property changes
         if (Model.START.equals(evt.getPropertyName())) {
            // change the color of the JPanel
            Color bg = model.isStart() ? START_COLOR : STOP_COLOR;
            setBackground(bg);
         }
      };
   }

}

是的，对于您非常简单的情况来说，这可能有点过头了，但它可以很好地扩展，因为您可以通过这种方式将模型和 GUI 问题分开。