Question

我正在用Java编写程序，但由于某种原因，我最底层组件中的滚动条不起作用。我不知道为什么。它应该在底部文本区域应用垂直滚动条。我做错了什么？

import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.*;
import javax.swing.Timer;
import java.text.*;
import java.lang.*;
import java.util.*;



public class TimerGui extends JFrame
{
private static final int FRAME_HEIGHT = 300;
private static final int FRAME_WIDTH = 600;

private JPanel topPanel;
private JPanel leftPanel;
private JPanel bottomPanel;

private JLabel topLabel;
private JLabel leftLabel;

private JTextField setTimer;
private JTextArea displayTimer;

private JScrollPane scrollPane;

private JButton startButton;

//no-arg constructor
public TimerGui()
{
    createTopPanel();
    createLeftPanel();
    createBottomPanel();
    setSize(FRAME_WIDTH, FRAME_HEIGHT);
}

//creates the top panel, including the label and text field 
private void createTopPanel()
{
    topPanel = new JPanel();
    topLabel = new JLabel("TIMER LAB:");

    final int FIELD_WIDTH = 10;
    setTimer = new JTextField(FIELD_WIDTH);

    topPanel.add(topLabel);
    topPanel.add(setTimer);

    add(topPanel, BorderLayout.NORTH);
}

//creates the left panel, which is just a single text label
private void createLeftPanel()
{
    leftPanel = new JPanel();
    leftLabel = new JLabel("(1000 milliseconds = 1 second)");

    add(leftPanel, BorderLayout.WEST);

    leftPanel.add(leftLabel);
}


//the listener for the start button
class ClickListener implements ActionListener
{
    public void actionPerformed(ActionEvent event)
    {
        int speed = Integer.parseInt(setTimer.getText());

        MyListner listener = new MyListner();
        Timer timer = new Timer(speed, listener);
        timer.start(); 
    }
}

class MyListner implements ActionListener
{
    public void actionPerformed(ActionEvent event)
    {         
        SimpleDateFormat simpleTime = new SimpleDateFormat("HH:mm:ss.SSS");
        Date now = new Date();
        String time = simpleTime.format(now);
        displayTimer.append(time + String.format("%n"));
    }
}

//creates the button, with action listener attached
private void createStartButton()
{
    startButton = new JButton("Start");

    ActionListener listener = new ClickListener();
    startButton.addActionListener(listener);
}

//creates the bottom panel, with the start button and the display text field
private void createBottomPanel()
{
    final int FIELD_WIDTH = 10;

    bottomPanel = new JPanel();
    displayTimer = new JTextArea(10, 15);
    displayTimer.setEditable(false);
    scrollPane = new JScrollPane(displayTimer);
       scrollPane.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);

    add(bottomPanel, BorderLayout.SOUTH);

    createStartButton();
    bottomPanel.add(startButton);
    bottomPanel.add(displayTimer);
    bottomPanel.add(scrollPane);
}

}

Answer 1

您正在添加displayTimer和JScrollPane，它们也将GUI保存到GUI。不要这样做。只需添加JScrollPane，因为您只能向GUI添加一次组件，因此最终添加一个没有JScrollPane的JTextArea和一个空的JScrollPane（仔细查看JTextArea的右侧）。所以改变这个：

    createStartButton();
    bottomPanel.add(startButton);
    bottomPanel.add(displayTimer);
    bottomPanel.add(scrollPane);

到此：

    createStartButton();
    bottomPanel.add(startButton);
    // !! bottomPanel.add(displayTimer);
    bottomPanel.add(scrollPane);

其他问题：

避免设置尺寸。
而是调用pack()并让GUI设置自己的大小。

滚动条不适用于Java

1 个答案: