JFrame中的滚动条未显示

Question

我正在尝试向我的JFrame添加一个水平滚动条，该滚动条本质上包含一堆JButton。在我的代码中，您可以看到我添加了19个绿色的JButton（称为“地面”）以及其他几个按钮。最后几个显然不在屏幕上。我想要实现一个滚动条，以便可以查看所有按钮。不幸的是，我似乎无法使JScrollPane滚动条正常工作。它会显示，但实际上不会滚动。

感谢您的反馈！

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

public class World {
    public static void main(String[] args) {
        // Just defining my own colour hues
        Color blue = new Color(77, 121, 255);
        Color green = new Color(0, 255, 0);
        Color grey = new Color(166, 166, 166);
        Color red = new Color(255, 102, 102);

        // Create the JFrame
        JFrame f = new JFrame("World");

        // Creating the JButtons. They're added to the JFrame at the end of the code.
        JButton object0 = new JButton("Object");
        object0.setBounds(0, 0, 80, 80);
        object0.setBackground(red);

        JButton object1 = new JButton("Object");
        object1.setBounds(80, 80, 80, 80);
        object1.setBackground(red);     

        // This just automatically adds the "Ground" buttons to the frame, as they are many of them.
        ArrayList<JButton> groundList = new ArrayList<JButton>();
        for (int i = 0; i < 19; i++) {
            groundList.add(new JButton("Ground"));
        }
        JButton temp;
        int x = 80;
        for (int i = 0; i < 19; i++) {
            temp = groundList.get(i);
            temp.setBounds(x, 0, 80, 80);
            temp.setBackground(green);
            f.add(temp);
            x = x + 80;
        }

        JButton wall = new JButton("Wall");
        wall.setBounds(80, 160, 80, 80);
        wall.setBackground(grey);

        JButton avatar = new JButton("Avatar");
        avatar.setBounds(0, 80, 80, 80);
        avatar.setBackground(blue);

        f.add(object0);
        f.add(object1);
        f.add(wall);
        f.add(avatar);      

        JScrollPane scroll = new JScrollPane(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS,ScrollPaneConstants.HORIZONTAL_SCROLLBAR_ALWAYS);
        scroll.setVisible(true);
        f.add(scroll);  // This adds the scroll bars but doesn't actually make them work.   
        f.setSize(800, 200);
        f.setVisible(true);     
    }
}

Answer 1

那是因为您需要将可滚动内容拖放到滚动条实例中。因此，您需要首先创建一个JPanel并将所有按钮添加到面板，然后创建JScrollPane并将面板传递给其构造函数。

将UI组件直接添加到JFrame并不是一个好习惯。

尝试运行此程序并检查更改，它应该可以工作：

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

public class World {
    public static void main(String[] args) {
        // Just defining my own colour hues
        Color blue = new Color(77, 121, 255);
        Color green = new Color(0, 255, 0);
        Color grey = new Color(166, 166, 166);
        Color red = new Color(255, 102, 102);

        // Create the JFrame
        JFrame f = new JFrame("World");
        //button will be added to this panel
        JPanel myPanel = new JPanel();

        // Creating the JButtons. They're added to the JFrame at the end of the code.
        JButton object0 = new JButton("Object");
        object0.setBounds(0, 0, 80, 80);
        object0.setBackground(red);

        JButton object1 = new JButton("Object");
        object1.setBounds(80, 80, 80, 80);
        object1.setBackground(red);     

        // This just automatically adds the "Ground" buttons to the frame, as they are many of them.
        ArrayList<JButton> groundList = new ArrayList<JButton>();
        for (int i = 0; i < 19; i++) {
            groundList.add(new JButton("Ground"));
        }
        JButton temp;
        int x = 80;
        for (int i = 0; i < 19; i++) {
            temp = groundList.get(i);
            temp.setBounds(x, 0, 80, 80);
            temp.setBackground(green);
            myPanel.add(temp);
            x = x + 80;
        }

        JButton wall = new JButton("Wall");
        wall.setBounds(80, 160, 80, 80);
        wall.setBackground(grey);

        JButton avatar = new JButton("Avatar");
        avatar.setBounds(0, 80, 80, 80);
        avatar.setBackground(blue);

        myPanel.add(object0);
        myPanel.add(object1);
        myPanel.add(wall);
        myPanel.add(avatar);      

        //notice how the panel is dropped inside the scroll pane
        JScrollPane scroll = new JScrollPane(myPanel, ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS,ScrollPaneConstants.HORIZONTAL_SCROLLBAR_ALWAYS);
        scroll.setVisible(true);
        //f.add(scroll);  // This adds the scroll bars but doesn't actually make them work. 

        //finally add the scroll to frame's content pane .. which is more proper than adding to frame directly
        f.getContentPane().add(scroll, BorderLayout.CENTER);
        f.setSize(800, 200);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
        f.setVisible(true);     
    }
}

但是

如果考虑将初始首选大小设置为面板，则所有按钮都将换行，并且不需要水平滚动：

myPanel.setPreferredSize(new Dimension(100, 200));

结果：