Question

我有一个包含两个JPanel的顶级容器（JFrame）。其中一个JPanel子项有一个属性将更改，并且需要触发其他一个JPanel组件（JProgressBar）的更新。

如何从触发属性更改的JPanel访问此组件？如果这不是正确的方法，是否有任何其他方法将属性更改传播给它？

Answer 1

听起来你需要使用某种Observer。这是一个简单的例子，让JFrame知道面板中的属性更改，然后相应地更新其他面板。如果您的设计变得复杂并且您有许多不同的组件必须了解彼此的变化，那么您应该考虑mediator pattern。

import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
 import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;


public class ObserverFrame extends JFrame {

  Panel1 panel;
  JPanel panel2;
  JLabel label;

 //to kick off the example
public static void main(String args[]){
    new ObserverFrame();        
}

//constructor of the JFrame
public ObserverFrame(){
    super("Observer Example");

    //the panel that we want to observe
    //notice that we pass a reference to the parent
    panel = new Panel1(this);
    add(panel, BorderLayout.NORTH);

    //another panel to be updated when the property changes
    panel2 = new JPanel();
    label = new JLabel("Panel to be updated");

    panel2.add(label);

    add(panel2, BorderLayout.SOUTH);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setSize(500, 500);
    setVisible(true);
}

//this method will be called by the panel when the property changes.
public void trigger(Panel1 panel) {
    label.setText(String.valueOf(panel.getProperty()));
}


//inner class for convenience of the example
class Panel1 extends JPanel{
    ObserverFrame parent;
    JButton b1;
    private int property;

    //accept the parent
    public Panel1(ObserverFrame p){
        this.parent = p;
        b1 = new JButton("Click Me");
        //click the button to change the property
        b1.addActionListener(new ActionListener(){
            public void actionPerformed(ActionEvent e){
                setProperty(getProperty() * 2); //update property here
            }
        });
        property = 10;
        add(b1);
    }

    //the property that we care about
    public int getProperty() {
        return property;
    }

    //when the setter is called, trigger the parent
    public void setProperty(int property) {
        this.property = property;
        parent.trigger(this);
    }


  }

}

如何从父组件（JFrame）访问子对象

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