JAVA GUI - 单击时我的提交按钮没有响应

Question

I am attempting to create a login GUI and when I press the submit button nothing happens. The other two buttons work as intended. I have attempted to add in a JOptionPane, but that seems to do nothing as well. Does anyone have any tips?

/**
 * Create contents of the window.
 */
protected void createContents() {
    shell = new Shell();
    shell.setBackground(SWTResourceManager.getColor(SWT.COLOR_TITLE_BACKGROUND_GRADIENT));
    shell.setSize(450, 300);
    shell.setText("Homework 1 GUI");
    
    CLabel lblHomework1Login = new CLabel(shell, SWT.NONE);
    lblHomework1Login.setBounds(141, 10, 149, 26);
    lblHomework1Login.setText("Homework 1 Login");
    
    CLabel lblUsername = new CLabel(shell, SWT.NONE);
    lblUsername.setBounds(10, 74, 76, 26);
    lblUsername.setText("Username");
    
    CLabel lblPassword = new CLabel(shell, SWT.NONE);
    lblPassword.setBounds(10, 129, 76, 26);
    lblPassword.setText("Password");
    
    txtUsername = new Text(shell, SWT.BORDER);
    txtUsername.setBounds(117, 74, 255, 26);
    
    txtPassword = new Text(shell, SWT.BORDER);
    txtPassword.setBounds(116, 129, 256, 26);
    
    Button btnSubmit = new Button(shell, SWT.BORDER);
    btnSubmit.setForeground(SWTResourceManager.getColor(SWT.COLOR_WIDGET_FOREGROUND));
    btnSubmit.addSelectionListener(new SelectionAdapter() {
        public void widgetSelected(SelectionEvent e) {
            String password = txtPassword.getText();
            String username = txtUsername.getText();
            
            // Implementing an action event listener class with conditional statement
            @Override
            public void actionPerformed(ActionEvent arg0) {
                String username = txtUsername.getText();
                String password = txtPassword.getText();

                if (username.equals("student1") && password.equals("987123"))
                    JOptionPane.showMessageDialog(null, "Login Successful");
                else
                    JOptionPane.showMessageDialog(null, "Username or Password mismatch ");
            }
            
            
        }
    });

Newest Edit and I am presented with the following error:Syntax error on token "MessageDialog", delete this token. Also the submit button still does not work. Thanks to all who have helped.

// Implementing an selection event listener class with conditional statement
            @Override
            public void handle(SelectionEvent onClick) {
                String Username = txtUsername.getText();
                String Password = txtPassword.getText();

                if (onClick.getSource() == btnSubmit)(Username.equals("student1") && Password.equals("987123"))
                    MessageDialog.openInformation(shell, "Login", "Login Successful");
                else
                    MessageDialog.openError(shell, "Login", "Username or Password mismatch");
            }
            
        }
    );
    
    

Answer 1

The code you show doesn't compile, you can't have a actionPerformed method nested in a widgetSelected method like that.

JOptionPane is a Java Swing class, do not try to mix Swing with SWT, they are different GUIs and are hard to make work together.

This code works for me:

shell.setSize(450, 300);
shell.setText("Homework 1 GUI");

shell.setLayout(new GridLayout(2, false));

Label lblHomework1Login = new Label(shell, SWT.NONE);
lblHomework1Login.setText("Homework 1 Login");
lblHomework1Login.setLayoutData(new GridData(SWT.BEGINNING, SWT.CENTER, false, false, 2, 1));

Label lblUsername = new Label(shell, SWT.NONE);
lblUsername.setText("Username");

Text txtUsername = new Text(shell, SWT.BORDER);
txtUsername.setLayoutData(new GridData(SWT.FILL, SWT.CENTER, true, false));

Label lblPassword = new Label(shell, SWT.NONE);
lblPassword.setText("Password");

Text txtPassword = new Text(shell, SWT.BORDER);
txtPassword.setLayoutData(new GridData(SWT.FILL, SWT.CENTER, true, false));

Button btnSubmit = new Button(shell, SWT.BORDER);
btnSubmit.setText("Submit");
btnSubmit.addSelectionListener(new SelectionAdapter() {
    @Override
    public void widgetSelected(final SelectionEvent e) {
        String password = txtPassword.getText();
        String username = txtUsername.getText();

        if (username.equals("student1") && password.equals("987123"))
          MessageDialog.openInformation(shell, "Login", "Login Successful");
        else
          MessageDialog.openError(shell, "Login", "Username or Password mismatch");
    }
});

Your btnSubmit had no text, I added some.

I have use the JFace MessageDialog for the messages, if you don't want to use JFace you could use the SWT MessageBox instead.

I have use Layouts rather than setBounds. setBounds should be avoided as it will not work well with different fonts.

To use MessageBox use:

 btnSubmit.addSelectionListener(new SelectionAdapter() {
     @Override
     public void widgetSelected(final SelectionEvent e) {
         String password = txtPassword.getText();
         String username = txtUsername.getText();

         MessageBox msgBox = new MessageBox(shell);
         if (username.equals("student1") && password.equals("987123"))
           msgBox.setMessage("Login Successful");
         else
           msgBox.setMessage("Username or Password mismatch");
         msgBox.open();
    }
 });

Answer 2

Whenever I used the Button class in my Java GUIs, I would always set up the buttons as so:

Button submitButton = new Button("Submit Button")
submitButton.setOnAction(this);

Then you would need the code to "hear" when the button is pressed. The following method "hears" that the button is pressed, then runs the following code:

@Override
    public void handle(ActionEvent onClick) {
        if (onClick.getSource() == submitButton)
        {
             // Do whatever you need to do
        }
    }

Perks of doing it this way:

• There is a lot less code to deal with
• All you need to do is change what the getSource() method is set equal to
• It's easier to read