如何在 TextField Java Swing 上获取价值
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how to get value on TextField Java Swing
提问by dientmUET
I have a simple Java Swing form with a JTextField, I get value on JTextFieldby getText()method but I can't use it to main program. Can you help me What problem and how to fix? This is my code :
我有一个带有 的简单 Java Swing 表单JTextField，我JTextField通过getText()方法获得了值，但我不能将它用于主程序。你能帮我什么问题以及如何解决？这是我的代码：
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.*;
public class Login {
private String name;
public Login() {
JFrame main = new JFrame("LOGIN");
main.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
main.setResizable(false);
main.setLayout(null);
main.setPreferredSize(new Dimension(200, 300));
main.setLocation(400, 200);
// Heading: LOGIN
JLabel heading = new JLabel("LOGIN");
heading.setBounds(80, 20, 50, 20);
main.add(heading);
// Label Username
JLabel username_label = new JLabel("username: ");
username_label.setBounds(5, 70, 80, 20);
main.add(username_label);
// Textfield Username
final JTextField username_field = new JTextField();
username_field.setBounds(70, 70, 120, 20);
main.add(username_field);
this.name = username_field.getText();
// Button Login
JButton loginBtn = new JButton("LOGIN");
loginBtn.setBounds(40, 150, 120, 25);
main.add(loginBtn);
main.pack();
main.setVisible(true);
loginBtn.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
name = username_field.getText();
// System.out.println(name); //IT WORKS
}
});
}
public static void main(String[] args) {
Login me = new Login();
me.print();//I EXPECT IT WILL PRINT @name BUT NO, WHY?
}
public void print() {
System.out.println(name);
}
}
Thanks very much!
非常感谢！
采纳答案by Keerthivasan
You shouldn't print the value before user clicks the button
您不应该在用户单击按钮之前打印该值
public static void main(String[] args) {
HelloWorldSwing me = new HelloWorldSwing();
//me.print();//DON't PRINT HERE
}
Instead, you can do this in actionPerformed() method,
相反，您可以在 actionPerformed() 方法中执行此操作，
loginBtn.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
name = username_field.getText();
HelloWorldSwing.this.print();
}
});
This will print the value, you enter in your text field
这将打印您在文本字段中输入的值
回答by Duncan Jones
You are trying to print the name value immediately after showing your GUI:
您尝试在显示 GUI 后立即打印名称值：
Login me = new Login();
me.print(); // This executes immediately after the statement above
But this value is not set until the user presses the login button:
但是这个值直到用户按下登录按钮才被设置：
loginBtn.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
name = username_field.getText();
// System.out.println(name); //IT WORKS
}
});
回答by Andrew Thompson
Adding a text field to a GUI class does not magically add a getText()method to that class. I mean think about it, if there were twotext fields, which one should be used for getText()? The field should be declared as an attribute of the class, and a method defined that will getText()of that field.
向 GUI 类添加文本字段并不会神奇地getText()向该类添加方法。我的意思是想想，如果有两个文本字段，应该使用哪一个getText()？该字段应声明为类的属性，并定义getText()该字段的意志的方法。
BTW:
顺便提一句：
- don't use a
JTextFieldwhen the GUI actually requires aJPasswordField. - Instead of
JFramethis should probably be a modalJDialog. See How to Use Modality in Dialogsfor details.
- 不使用
JTextField时，GUI实际需要JPasswordField。 - 而不是
JFrame这应该是一个 modalJDialog。有关详细信息，请参阅如何在对话框中使用模态。
