java - JFrame getWidth() 和 getHeight() 即使在 pack() 之后也返回 0

Question

我已经查看了涉及这种情况的其他问题，但它仍然为我返回 0，并且包只是缩小了整个 GUI，因此它不是原始大小。

这是我的框架窗口:

package io.ryankshah;

import java.awt.Dimension;
import java.awt.FlowLayout;

import javax.swing.JComponent;
import javax.swing.JFrame;

public class ChatWindow extends JFrame
{
    private JComponent loginPanel;

    /**
     * Creates a default chat window object
     */
    public ChatWindow() {
        super("Secure Client/Server Chat");

        loginPanel = new LoginPanel(this);

        setSize(new Dimension(800, 600));   
        setResizable(false);
        setDefaultCloseOperation(EXIT_ON_CLOSE);

        addComponents();
        pack();

        setLocationRelativeTo(null);
        setVisible(true);
    }

    /**
     * Adds all chat-related components to the main frame
     */
    private void addComponents() {
        add(loginPanel);
    }

    public static void main(String[] args) {
        new ChatWindow();
    }
}

最后是我的 LoginPanel，其中调用了 getContentPane().getWidth():

package io.ryankshah;

import java.awt.Graphics;
import java.io.DataOutputStream;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;

import javax.net.ssl.HttpsURLConnection;
import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JPasswordField;
import javax.swing.JTextField;

public class LoginPanel extends JPanel
{
    private List<JComponent> loginComponents;
    private JTextField username;
    private JPasswordField password;
    private JButton login;

    private static final String USER_AGENT = "Mozilla/5.0";
    private static final int INPUT_WIDTH = 400;
    private static final int INPUT_HEIGHT = 30;

    /**
     * Creates a default login panel object
     * @param parent The parent container of the panel
     */
    public LoginPanel(JFrame parent) {
        setLayout(null);

        loginComponents = new ArrayList<JComponent>();
        username = new JTextField();
        password = new JPasswordField();
        login = new JButton("Login");

        loginComponents.add(username);
        loginComponents.add(password);
        loginComponents.add(login);

        int j = parent.getContentPane().getHeight();
        int componentCenter = (parent.getWidth() / 2) - (INPUT_WIDTH / 2);
        for(int i = 0; i < loginComponents.size(); i++) {
            JComponent jc = loginComponents.get(i);
            System.out.println(parent.getContentPane().getWidth());
            jc.setBounds(componentCenter, j % (i + 1), INPUT_WIDTH, INPUT_HEIGHT);
            add(jc);
        }
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
    }

    @Override
    public void update(Graphics g) {
        super.update(g);
    }

    //TODO: create case method for getting any field value
    /**
     * Gets the username from the username field
     * @return Returns the username from the username field
     */
    public String getUsername() {
        return username.getText();
    }

    /**
     * Gets the password from the password field
     * @return Returns the password from the password field
     */
    public String getPassword() {
        return new String(password.getPassword());
    }

    /**
     * Creates a login request to the server returns the result
     * @param url URL the request is sent to
     * @return result Result of the request
     */
    public void createLoginRequest(String url) throws Exception {
        URL urlObj = new URL(url);
        HttpsURLConnection connection = (HttpsURLConnection) urlObj.openConnection();

        connection.setRequestMethod("POST");
        connection.setRequestProperty("User-Agent", USER_AGENT);
        connection.setRequestProperty("Accept-Language", "en-US,en;q=0.5");
        connection.setDoOutput(true);

        String params = "username="+getUsername()+"&password="+getPassword();
        DataOutputStream dos = new DataOutputStream(connection.getOutputStream());

        dos.writeBytes(params);
        dos.flush();
        dos.close();
    }
}

Answer 1

作为对您的评论的回应，当您调用它时:

loginPanel = new LoginPanel(this);

您正在传递未显示的 JFrame。所以此时，它的高和宽都为0。

在您的 LoginPanel 类中，当您调用:

int componentCenter = (parent.getWidth() / 2) - (INPUT_WIDTH / 2);

parent.getWidth()/2 将使用 0。

这将导致您的边界被设置为负值。这可能不是你想要的