摆动组件不可见

Question

当我运行代码时，只有空白框。 要查看JButton和JTextField，我必须先搜索并单击它们，然后才能看到它们。 我在Internet上到处搜索，但是什么也没找到。 我还将可见性设置为true并添加了JComponents。 这是我的代码：

Frame Fenster = new Frame();

和这个...

package me.JavaProgramm;

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.text.NumberFormat;
import java.text.ParseException;
import java.util.Locale;

public class Frame extends JFrame {
    private JButton bChange;
    private JTextField tvonEur;
    private JTextField tzuOCur; //andere Währung (other Currency)
    private JTextField tzuEur;
    private JTextField tvonOCur;
    private JComboBox cbCur; //Wärhung wählen
    private String curName;
    private double faktorUSD;
    private double faktorGBP;

    private static String[] comboCur = {"USD", "GBP"};

    public Frame() {
        setLayout(null);
        setVisible(true);
        setSize(400, 400);
        setTitle("Währungsrechner");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setAlwaysOnTop(true);
        setResizable(false);

        Font schrift = new Font("Serif", Font.PLAIN + Font.ITALIC, 30);

        tvonEur = new JTextField("Euro");
        tvonEur.setSize(80, 25);
        tvonEur.setLocation(20, 50);
        tvonEur.requestFocusInWindow();
        tvonEur.selectAll();

        tzuEur = new JTextField("Euro");
        tzuEur.setSize(80, 25);
        tzuEur.setLocation(20, 150);
        tzuEur.requestFocusInWindow();
        tzuEur.selectAll();

        bChange = new JButton("Euro zu US-Dollar");
        bChange.setSize(120, 25);
        bChange.setLocation(110, 50);

        tzuOCur = new JTextField("US-Dollar");
        tzuOCur.setSize(80, 25);
        tzuOCur.setLocation(240, 50);
        tzuOCur.requestFocusInWindow();
        tzuOCur.selectAll();

        tvonOCur = new JTextField("US-Dollar");
        tvonOCur.setSize(80, 25);
        tvonOCur.setLocation(240, 50);
        tvonOCur.requestFocusInWindow();
        tvonOCur.selectAll();

        cbCur = new JComboBox(comboCur);
        cbCur.setSize(100, 20);
        cbCur.setLocation(100, 100);

        tvonEur.setVisible(true);
        tzuEur.setVisible(true);
        tzuOCur.setVisible(true);
        tvonOCur.setVisible(true);
        bChange.setVisible(true);
        cbCur.setVisible(true);

        add(tvonEur);
        add(bChange);
        add(tzuOCur);
        add(cbCur);

        Currency currency = new Currency();

        String strUSD = currency.convertUSD();
        try {
            NumberFormat formatUSD = NumberFormat.getInstance(Locale.GERMANY);
            Number numberUSD = formatUSD.parse(strUSD);
            faktorUSD = numberUSD.doubleValue();
            System.out.println(faktorUSD);
        } catch (ParseException e) {
            System.out.println(e);
        }

        String strGBP = currency.convertGBP();
        try {
            NumberFormat formatGBP = NumberFormat.getInstance(Locale.GERMANY);
            Number numberGBP = formatGBP.parse(strGBP);
            faktorGBP = numberGBP.doubleValue();
            System.out.println(faktorGBP);
        } catch (ParseException e) {
            System.out.println(e);
        }

        cbCur.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                cbCur = (JComboBox) e.getSource();
                curName = (String) cbCur.getSelectedItem();
                if (curName == "USD") {
                    tzuOCur.setText("US-Dollar");
                } else if (curName == "GBP") {
                    tzuOCur.setText("British-Pound");
                }
            }
        });

        bChange.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                if (curName == "USD") {
                    try {
                        Double doubleEUR = Double.parseDouble(tvonEur.getText());
                        Double doubleUSD = doubleEUR * faktorUSD;
                        tzuOCur.setText(Double.toString(roundScale3(doubleUSD)));
                    } catch (NumberFormatException nfe) {
                        System.out.println("Gebe einen richten Wert ein!");
                    }
                } else if (curName == "GBP") {
                    try {
                        Double doubleEUR = Double.parseDouble(tvonEur.getText());
                        Double doubleGBP = doubleEUR * faktorGBP;
                        tzuOCur.setText(Double.toString(roundScale3(doubleGBP)));
                    } catch (NumberFormatException nfe) {
                        System.out.println("Gebe einen richten Wert ein!");
                    }
                }
            }
        });
    }

    public static double roundScale3(double d) {
        return Math.rint(d * 1000) / 1000.;
    }
}

Answer 1

将子级添加到父容器后，尝试移动setVisible(true) 。

通常，在Swing中，最好将代码更新可见的组件放在事件分派线程中，例如：

SwingUtilities.invokeLater(new Runnable() {
  @Override
  public void run() {
    Frame.this.setVisible(true);
  }
});