使用 ActionListener 调用递归树方法

Question

我的问题有点难以表达，但基本上这就是我想要做的：我有一个家庭作业来绘制一个递归树，用户可以选择显示的节点数量。我有一个使用递归绘制树的绘制方法，我需要程序接受来自文本字段的用户输入。我是递归新手，但我和室友设法使用 Graphics2D 绘制了一些东西，但我们无法开始弄清楚如何允许用户选择节点数量。输入字段的骨架在那里，但它没有做任何事情，因为我没有 ActionListener 并且不完全知道将什么放入 ActionListener 以允许用户输入值。任何帮助将不胜感激。谢谢！

import java.awt.*;
import javax.swing.*;

public class Tree extends JPanel {

    private static final long serialVersionUID = 1L;
    private JLabel num; //tells user to enter number of nodes
    private JTextField in; //text field for user input

    public Tree() {
        num = new JLabel("Number of Branches: ");
        add(num);
        in = new JTextField(5);
        add(in);
    }

    private void draw(Graphics2D g, int n, int x, int y) {
        if (n == 0) {
            return;
        } else {
            int angle = 45;
            int length = 50;
            g.drawLine(x, y, x, y - length); // trunk
            g.setColor(Color.BLACK);
            g.rotate(Math.toRadians(-angle), x, y - length); // left
            // branch
            draw(g, n - 1, x, y - length);
            g.rotate(Math.toRadians(angle), x, y - length);
            g.rotate(Math.toRadians(angle), x, y - length); // right
            // branch
            draw(g, n - 1, x, y - length);
            g.rotate(Math.toRadians(-angle), x, y - length);
        }
    }

    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D gg = (Graphics2D) g;
        draw(gg, 3, getWidth() / 2, getHeight() / 2);
    }

    public static void main(String[] args) {
        Tree tree = new Tree();
        tree.setPreferredSize(new Dimension(500, 500));
        JFrame frame = new JFrame("Test");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add(tree);
        frame.setSize(500, 500);
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }
}

Answer 1

我个人会使用 MVC（模型-视图-控制器）模型来组织我的代码，保持两者之间的显示、处理和通信都是分开的。这样更容易跟踪正在发生的事情。在您的情况下，树对象是绘图、标签和按钮。但是由于您已经编写了代码，因此调整它会更容易。

要添加一个动作监听器，您需要将用户输入注册为一个事件和一个按钮来“捕获它”。这种意义上的事件将是用户按下按钮。因此，一旦用户输入节点数并按下按钮，动作监听器就会响应此事件并执行所需的代码（绘制树）。

我会这样做：

• 给树对象一个可变的节点号。
• 创建一个实现 actionListener 的类。
• 创建一个按钮并为其分配一个 actionListener。
• 创建对绘制树的静态引用，单击按钮后更改其节点号，并在屏幕上更新它。

导入 java.awt.*;

导入 javax.swing.*;

公共类树扩展 JPanel {

private static final long serialVersionUID = 1L;

// I made all components static since you only need one copy of each
private static JLabel num; //tells user to enter number of nodes
private static JTextField in; //text field for user input
private static JButton enter = new JButton("Enter");// create a button to capture event

private static Tree tempTree; 

private int nodeNumber;   // makes a tree's node number changeable

public Tree() {

    this.nodeNumber = 0;
    num = new JLabel("Number of Branches: ");
    add(num);
    in = new JTextField(5);
    add(in);
    add(enter);
    add(enter);
}



private void draw(Graphics2D g, int n, int x, int y) {
    if (n == 0) {
        return;
    } else {
        int angle = 45;
        int length = 50;
        g.drawLine(x, y, x, y - length); // trunk
        g.setColor(Color.BLACK);
        g.rotate(Math.toRadians(-angle), x, y - length); // left
        // branch
        draw(g, n - 1, x, y - length);
        g.rotate(Math.toRadians(angle), x, y - length);
        g.rotate(Math.toRadians(angle), x, y - length); // right
        // branch
        draw(g, n - 1, x, y - length);
        g.rotate(Math.toRadians(-angle), x, y - length);
    }
}

// I had to overload your draw method to one in which I can change the drawing multiple times later
private void draw(Graphics2D g, int x, int y)
{
        int n = this.nodeNumber;
       if (n == 0) {
           return;
       } else {
           int angle = 45;
           int length = 50;
           g.drawLine(x, y, x, y - length); // trunk
           g.setColor(Color.BLACK);
           g.rotate(Math.toRadians(-angle), x, y - length); // left
           // branch
           draw(g, n - 1, x, y - length);
           g.rotate(Math.toRadians(angle), x, y - length);
           g.rotate(Math.toRadians(angle), x, y - length); // right
           // branch
           draw(g, n - 1, x, y - length);
           g.rotate(Math.toRadians(-angle), x, y - length);
       }
}

//makes a tree's node number editable
public void setNodeNumber(int number)
{
    this.nodeNumber = number;
}

protected void paintComponent(Graphics g) {
    super.paintComponent(g);
    Graphics2D gg = (Graphics2D) g;

    //this version can change node number
    draw(gg,getWidth() / 2, getHeight() / 2);
}

public static void main(String[] args) {

    Tree tree = new Tree();
    tree.setPreferredSize(new Dimension(500, 500));
    JFrame frame = new JFrame("Test");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.getContentPane().add(tree);
    frame.setSize(500, 500);

    // stores the currently displayed tree for later changes
    Tree.tempTree = tree;
    Listener enterListener = new Listener();

    Tree.enter.setActionCommand("ENTER");
    Tree.enter.addActionListener(enterListener);


    frame.setLocationRelativeTo(null);
    frame.setVisible(true);


}

// refreshes tree
public static void refreshTree()
{



    int inputNumber;

    // checks if input is a number or not
    try
    {
        //gets input node number 
        inputNumber =  Integer.parseInt(Tree.in.getText());

        //sets node number 
        Tree.tempTree.setNodeNumber(inputNumber);
        // updates tree
        Tree.tempTree.updateUI();
    }
    catch(NumberFormatException e)
    {
        System.out.println(" Invalid node Number " + e);
    }



}

}

您还需要一个动作监听器类：

导入 java.awt.event.ActionEvent; 导入 java.awt.event.ActionListener;

公共类监听器实现 ActionListener{

@Override
public void actionPerformed(ActionEvent event) {
    String action = event.getActionCommand();
    if(action.equals("ENTER"))
    {

        Tree.refreshTree();
    }


}

}