java - 如何多次创建新的和处置jcomponents？

Question

(抱歉，如果这个问题没有正确完成，我是新人。但至少在问自己的问题之前我做了很多研究)

你好。我正在用 Java 编写一个二十一点游戏，它变得相当庞大。 我的问题是如何处理swing组件的多个实例，我想你可以这样调用它。我不知道是否要在类级别或特定方法中创建组件(例如 jpanels 和 jbuttons)。

如果我在相应的方法中创建它们，那么我的操作监听器将看不到它们，但如果我将它们创建为类级别，那么当我调用 dispose() 时它们会被删除。

 class BlackjackGame extends JFrame implements ActionListener{

    public void mainMenu(){

        JPanel menuPane = new JPanel(new GridBagLayout()); //Init of main menu
        GridBagConstraints c = new GridBagConstraints();
        menuPane.setBackground(new Color(125,0,0));
        menuPane.setBounds(620,220,175,250);

        JLabel menuTitle = new JLabel("Welcome to Blackjack!");//Main menu-content
        c.gridx = 1;
        c.gridy = 0;
        c.insets = new Insets(0,0,20,0);
        menuPane.add(menuTitle, c);

        JButton playButton = new JButton("Play!");
        playButton.addActionListener(this);
        c.gridx = 0;
        c.gridy = 1;
        c.gridwidth = 3;
        c.ipadx = 25;
        c.ipady = 25;
        c.insets = new Insets(0,0,0,0);
        menuPane.add(playButton, c);

        JButton exitButton = new JButton("Exit!");
        exitButton.addActionListener(this);
        c.gridx = 0;
        c.gridy = 2;
        c.gridwidth = 3;
        menuPane.add(exitButton, c);

        JButton rulesButton = new JButton("Set rules.");
        rulesButton.addActionListener(this);
        c.gridx = 0;
        c.gridy = 3;
        c.gridwidth = 3;
        menuPane.add(rulesButton, c);

        this.add(menuPane,0);
    }

    //This is where I get problems
    public void actionPerformed (ActionEvent event){
        if(event.getSource() == playButton){
            //I want the menuPane to disappear, and a transition into the game.
            menuPane.dispose();
            //Call method for the rest of the game.

        }else if(event .getSource() etcetera etcetera){
            etcetera etcetera
        }
    }
}

以这种方式完成后， Action 监听器无法找到我的组件，例如 playButton 或 menuPane。但如果我将它们作为类级别对象引入:

class BlackjackGame extends JFrame implements ActionListener{

    JPanel menuPane = new JPanel(new GridBagLayout());
    JLabel menuTitle = new JLabel("Welcome to Blackjack!");
    JButton playButton = new JButton("Play!");
    JButton exitButton = new JButton("Exit!");
    JButton rulesButton = new JButton("Set rules.");

    public void mainMenu(){
        //Rest of code
    }

    public void actionPerformed(ActionEvent event){
        menuPane.dispose();
        //Rest of code
    }
}

...然后当我调用 menuPane.dispose() 时，当我想再次调用 mainMenu() 时如何取回它？如果我想返回主菜单，那么我需要创建一个新的 menuPane 实例以及所有按钮，但由于它们是类级别并且已经被处理，所以我不能。

请帮助我，谢谢!

PS。如果有帮助的话，我可以发布我的完整代码，因为它是 atm。

编辑:丹的答案已被接受，因为它确实是正确的答案，并且它非常适合我的特定程序。谢谢你，圣诞快乐!

Answer 1

首先，除非我误解了你的代码，menuPane.dispose()不应该像 JPanel 一样工作没有名为 dispose() 的函数

如果您想使用相同的 menuPane 做您想做的事情的最佳方式对于菜单。而不是menuPane.dispose();使用remove(menuPane);然后add(yourOtherPanel);

工作示例

import java.awt.Color;
import java.awt.EventQueue;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Insets;
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;

@SuppressWarnings("serial")
public class BlackjackGame extends JFrame implements ActionListener {
    private JPanel menuPane;
    private JLabel menuTitle;
    private JButton playButton;
    private JButton exitButton;
    private JButton rulesButton;

    private JPanel otherPane;
    private JLabel otherTitle;
    private JButton otherButton;

    public BlackjackGame() {
        mainMenu();
        otherPanel();
        setSize(400, 400);
        setVisible(true);
    }

    private void mainMenu() {

        menuPane = new JPanel(new GridBagLayout());
        GridBagConstraints c = new GridBagConstraints();
        menuPane.setBackground(new Color(125,0,0));
        menuPane.setBounds(620,220,175,250);

        menuTitle = new JLabel("Welcome to Blackjack!");
        c.gridx = 1;
        c.gridy = 0;
        c.insets = new Insets(0,0,20,0);
        menuPane.add(menuTitle, c);

        playButton = new JButton("Play!");
        playButton.addActionListener(this);
        c.gridx = 0;
        c.gridy = 1;
        c.gridwidth = 3;
        c.ipadx = 25;
        c.ipady = 25;
        c.insets = new Insets(0,0,0,0);
        menuPane.add(playButton, c);

        exitButton = new JButton("Exit!");
        exitButton.addActionListener(this);
        c.gridx = 0;
        c.gridy = 2;
        c.gridwidth = 3;
        menuPane.add(exitButton, c);

        rulesButton = new JButton("Set rules.");
        rulesButton.addActionListener(this);
        c.gridx = 0;
        c.gridy = 3;
        c.gridwidth = 3;
        menuPane.add(rulesButton, c);

        add(menuPane);
    }

    private void otherPanel() {
        otherPane = new JPanel(new GridBagLayout());
        GridBagConstraints c = new GridBagConstraints();
        otherPane.setBackground(new Color(125,0,0));
        otherPane.setBounds(620,220,175,250);

        otherTitle = new JLabel("Welcome to Second Pane!");
        c.gridx = 1;
        c.gridy = 0;
        c.insets = new Insets(0,0,20,0);
        otherPane.add(otherTitle, c);

        otherButton = new JButton("Go Back!");
        otherButton.addActionListener(this);
        c.gridx = 0;
        c.gridy = 1;
        c.gridwidth = 3;
        c.ipadx = 25;
        c.ipady = 25;
        c.insets = new Insets(0,0,0,0);
        otherPane.add(otherButton, c);
    }

    public void actionPerformed (ActionEvent event) {
        if(event.getSource() == playButton) {
            remove(menuPane);
            add(otherPane);
            validate();
            repaint();

        } else if(event.getSource() == otherButton) {
            remove(otherPane);
            add(menuPane);
            validate();
            repaint();
        }
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(() -> new BlackjackGame());
    }
}

编辑评论

所以java方法 remove() 仅从容器中删除对象，在本例中为 JFrame 。此方法不会影响其移动的对象，因此可以稍后重用该对象。因此，为什么在上面的代码中我只能使用 remove()和add()无需重新声明或重新制作的方法menuPane和otherPane .

至于为什么我这样声明对象

`private JPanel menuPane;`

然后像这样初始化

menuPane = new JPanel(new GridBagLayout());

这是因为我想要ActionListener能够在不立即初始化对象的情况下查看它们。专线private JPanel menuPane;使对象成为全局变量，并且行 menuPane = new JPanel(new GridBagLayout());使它成为我将要使用的东西。这样做而不是 JPanel menuPane = new JPanel(new GridBagLayout());也意味着我可以在多个方法中重用同一个变量。例如

private JPanel panel;

private void createPanelOne() {
    panel = new JPanel(new FlowLayout());
    ...
    add(panel);
}

private void createPanelTwo() {
    panel = new JPanel(new GridBagLayout());
    ...
    add(panel);
}

完成此操作后，您将有两个 JPanel在你的 JFrame 中它们会有所不同，但您只需要使用一个 JPanel

这是声明它的另一种方式，它创建一个局部变量。局部变量对于您正在使用的方法之外的其他方法不可见，除非您传递它们。

JPanel panel = new JPanel();

我不会说这是一个骗局。我认为有时最好在一个方法中使用其他方法不可见的局部变量。

最后，要将局部变量传递给其他方法，您可以在您创建的方法中使用参数。例如

public void setSomeValue(int val) {
    someValue = val;
}