java swing JTextField 设置PlaceHolder [英] java swing JTextField set PlaceHolder

问题描述

我创建了一个 JTextField，现在我想在该 JTextField 上设置占位符，但我不知道如何设置?请帮忙.这是我的代码:

I created a JTextField and now I want to set the placeholder on that JTextField, but I don't know how? Please help. Here is my code:

JTextField database=new JTextField("Enter Data Base Name");
database.setPreferredSize(database.getPreferredSize());
database.setText("");

推荐答案

试试这个类:

package playground;

import java.awt.*;

import javax.swing.*;
import javax.swing.text.Document;

@SuppressWarnings("serial")
public class PlaceholderTextField extends JTextField {

    public static void main(final String[] args) {
        final PlaceholderTextField tf = new PlaceholderTextField("");
        tf.setColumns(20);
        tf.setPlaceholder("All your base are belong to us!");
        final Font f = tf.getFont();
        tf.setFont(new Font(f.getName(), f.getStyle(), 30));
        JOptionPane.showMessageDialog(null, tf);
    }

    private String placeholder;

    public PlaceholderTextField() {
    }

    public PlaceholderTextField(
        final Document pDoc,
        final String pText,
        final int pColumns)
    {
        super(pDoc, pText, pColumns);
    }

    public PlaceholderTextField(final int pColumns) {
        super(pColumns);
    }

    public PlaceholderTextField(final String pText) {
        super(pText);
    }

    public PlaceholderTextField(final String pText, final int pColumns) {
        super(pText, pColumns);
    }

    public String getPlaceholder() {
        return placeholder;
    }

    @Override
    protected void paintComponent(final Graphics pG) {
        super.paintComponent(pG);

        if (placeholder == null || placeholder.length() == 0 || getText().length() > 0) {
            return;
        }

        final Graphics2D g = (Graphics2D) pG;
        g.setRenderingHint(
            RenderingHints.KEY_ANTIALIASING,
            RenderingHints.VALUE_ANTIALIAS_ON);
        g.setColor(getDisabledTextColor());
        g.drawString(placeholder, getInsets().left, pG.getFontMetrics()
            .getMaxAscent() + getInsets().top);
    }

    public void setPlaceholder(final String s) {
        placeholder = s;
    }

}

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