JDialog没有正确设置首选大小？

Question

我真的不明白这里发生了什么。我有一个程序，我想在其中使用 JDialog，但我想要一个单独的类，所以我扩展了 JDialog 的类，去设置它的首选大小，但它似乎没有设置它正确。我制作了一个按钮来“取消”JDialog 将执行的操作，该操作应该位于 JDialog 的右下角，但它不会去那里。相反，它在它之外，只有在我调整 JDialog 的大小时才会显示。

我完全不知道发生了什么，或者我是否遗漏了一些愚蠢的东西，但我们非常感谢任何帮助。

代码如下：

import java.awt.*;
import java.awt.event.*;

import javax.swing.*;

public class NewPlatformDialog extends JDialog implements ActionListener {
private LevelEditor le;

private JButton cancel = new JButton("cancel");

public NewPlatformDialog(Frame owner, String title, LevelEditor l) {
    super(owner, title, Dialog.ModalityType.APPLICATION_MODAL);
    le = l;
    setLayout(null);
    setDefaultCloseOperation(DISPOSE_ON_CLOSE);
    setPreferredSize(new Dimension(300, 200));

    add(cancel);
    setLocation((owner.getLocationOnScreen().x + (owner.getLocationOnScreen().x + owner.getWidth()))/2 - getPreferredSize().width/2
            , (owner.getLocation().y + (owner.getLocationOnScreen().y + owner.getHeight()))/2 - getPreferredSize().height/2);

    cancel.setBounds(getPreferredSize().width - cancel.getPreferredSize().width - 10, 
            getPreferredSize().height - cancel.getPreferredSize().height - 10,
            cancel.getPreferredSize().width, cancel.getPreferredSize().height);
    cancel.addActionListener(this);
    cancel.setFocusable(false);

    pack();
    setVisible(true);
}

public void actionPerformed(ActionEvent e) {
    Object source = e.getSource();
    if(source == cancel) dispose();
}
}

对不起，有点乱，我复制粘贴的时候有点搞砸了。

带有布局的更新代码

import java.awt.*;
import java.awt.event.*;

import javax.swing.*;

public class NewPlatformDialog extends JDialog implements ActionListener {
private LevelEditor le;
private String[] options = {
        "Standard Platform",
        "Boost Platform",
        "Moving Platform",
        "Death Platform"
};
private JComboBox<String> platformSelector = new JComboBox<String>(options);

private JButton cancel = new JButton("cancel");

CardLayout cl = new CardLayout();

private JPanel typeSelect = new JPanel(new FlowLayout(FlowLayout.LEFT));
private JPanel panelContainer = new JPanel();
private JPanel standardPlatform = new JPanel();
private JPanel boostPlatform = new JPanel();
private JPanel movingPlatform = new JPanel();
private JPanel deathPlatform = new JPanel();
private JPanel buttonPanel = new JPanel();

public NewPlatformDialog(Frame owner, String title, LevelEditor l) {
    super(owner, title, Dialog.ModalityType.APPLICATION_MODAL);
    setDefaultCloseOperation(DISPOSE_ON_CLOSE);
    setLayout(new BoxLayout(getContentPane(), BoxLayout.Y_AXIS));
    setResizable(false);

    cl.setVgap(10);
    panelContainer.setLayout(cl);
    le = l;

    platformSelector.addActionListener(this);
    platformSelector.setFocusable(false);
    platformSelector.setSize(100, 70);
    platformSelector.setFont(new Font("", Font.BOLD, 12));
    platformSelector.setMaximumSize(new Dimension(200, platformSelector.getPreferredSize().height));
    platformSelector.setMinimumSize(new Dimension(200, platformSelector.getPreferredSize().height));

    add(typeSelect);
    add(panelContainer);
    add(buttonPanel);

    panelContainer.add(standardPlatform, "1");
    panelContainer.add(boostPlatform, "2");
    panelContainer.add(movingPlatform, "3");
    panelContainer.add(deathPlatform, "4");
    panelContainer.setMaximumSize(new Dimension(500, 500));
    panelContainer.setMinimumSize(new Dimension(20, 20));

    createTypeSelect();
    createStandardPlatformPanel();
    createButtonPanel();

    cl.show(panelContainer, "1");

    pack();
    setVisible(true);
}

public void actionPerformed(ActionEvent e) {
    Object source = e.getSource();
    if(source == cancel) dispose();
    else if(source == platformSelector) {
        if(platformSelector.getSelectedIndex() == 0) {
            cl.show(panelContainer, "1");
            createStandardPlatformPanel();
        }
        else if(platformSelector.getSelectedIndex() == 1) {
            cl.show(panelContainer, "2");
            createBoostPlatformPanel();
        }
        else if(platformSelector.getSelectedIndex() == 2) {
            cl.show(panelContainer, "3");
            createMovingPlatformPanel();
        }
        else if(platformSelector.getSelectedIndex() == 3) {
            cl.show(panelContainer, "4");
            createDeathPlatformPanel();
        }
    }
}

private void createTypeSelect() {
    typeSelect.add(new JLabel("Platform Type: ")).setFont(new Font("", Font.PLAIN, 14));
    typeSelect.add(platformSelector);
}

private void createStandardPlatformPanel() {
    panelContainer.setPreferredSize(new Dimension(200, 200));
    standardPlatform.setBackground(Color.BLUE);
    pack();
}

private void createBoostPlatformPanel() {
    panelContainer.setPreferredSize(new Dimension(500, 500));
    boostPlatform.setBackground(Color.RED);
    pack();
}

private void createMovingPlatformPanel() {
    panelContainer.setPreferredSize(new Dimension(50, 50));
    movingPlatform.setBackground(Color.YELLOW);
    pack();
}

private void createDeathPlatformPanel() {
    panelContainer.setPreferredSize(new Dimension(100, 100));
    deathPlatform.setBackground(Color.GRAY);
    pack();
}

private void createButtonPanel() {
    cancel.addActionListener(this);
    cancel.setFocusable(false);
    cancel.setAlignmentX(Box.RIGHT_ALIGNMENT);
    buttonPanel.add(cancel);
}

/*
 * 
    add(cancel);
    setLocation((owner.getLocationOnScreen().x + (owner.getLocationOnScreen().x + owner.getWidth()))/2 - getPreferredSize().width/2
            , (owner.getLocation().y + (owner.getLocationOnScreen().y + owner.getHeight()))/2 - getPreferredSize().height/2);

    cancel.setBounds(getPreferredSize().width - cancel.getPreferredSize().width - 10, 
            getPreferredSize().height - cancel.getPreferredSize().height - 10,
            cancel.getPreferredSize().width, cancel.getPreferredSize().height);
    cancel.addActionListener(this);
    cancel.setFocusable(false);
 */
}

抱歉，这明显更多

Answer 1

出现问题是因为对话框的首选大小包括窗口的标题栏以及任何其他窗口装饰。但是，窗口内的位置是从内容窗格的左上角设置的。由于这种差异，大多数窗口管理器都会让您的按钮最终靠得太右，而靠得太远。

正确的解决方案是使用实际的布局管理器，它将正确定位您的组件。这是一个将按钮放在您想要的位置的示例：

setLayout(new BorderLayout());
JPanel bottom = new JPanel();
bottom.setLayout(new BorderLayout());
bottom.setBorder(BorderFactory.createEmptyBorder(10,10,10,10));
bottom.add(new JPanel(), BorderLayout.CENTER);
bottom.add(cancel, BorderLayout.EAST);
add(new JPanel(), BorderLayout.CENTER);
add(bottom, BorderLayout.SOUTH);

如果您坚持使用null 布局，您可以将代码更改为使用getContentPane().setPreferredSize(new Dimension(300, 200))，这将使您的框架为窗口装饰添加必要的空间。但是，我强烈建议您不要这样做。使用null 布局是considered a bad practice。