Java - 文本字段上的占位符 [英] Java - placeholder on textfield

问题描述

我正在尝试使用Swing创建GUI。我的问题是，我有一个文本字段，但我希望它有一个占位符（如在html中）。我在这里和那里读到它可以通过覆盖textfield的paint（）来完成。

I'm trying to create a GUI with Swing. My problem is, I have a textfield, but I want it to have a "placeholder" (like in html). I read here and there that it can be done by overriding the paint() of the textfield.

由于我的代码生成，我发现我需要使用自定义创建代码覆盖生成的代码。

Since my code is generated I found out that I need to use the "Custom Creation Code" to override the code that was generated.

以下是我在自定义创建代码字段中添加的内容

Here is what I have put in the "Custom Creation Code" field

new javax.swing.JTextField()
{
    String test = super.getText();
    String hint = "Username";

    public void paint(Graphics g)
    {
        if ( test == null || test.length() < 1 ) {
            g.setColor( Color.red );
            g.drawString(hint, 0, 0);
        }

        g.setColor(Color.BLACK);
        super.paint(g);
    }
}

这会产生以下输出

javax.swing.JTextField username = new javax.swing.JTextField()
{
    String test = super.getText();
    String hint = "Username";

    public void paint(Graphics g)
    {
        if ( test == null || test.length() < 1 ) {
            g.setColor( Color.red );
            g.drawString(hint, 0, 0);
        }

        g.setColor(Color.BLACK);
        super.paint(g);
    }
};

现在我看到textField但是里面什么都没有，也许我需要添加一些功能到某些事件，但我不确定。

For now I see the textField but there is nothing in it, maybe I need to add some function onto some event, but I am not sure.

如果有人能伸出援手，我将不胜感激。

I would be grateful if anyone could lend a hand.

编辑：以下是我想要做的演示： http://davidwalsh.name/demo/ html5-placeholder.php

EDIT : Here is a demo of what I want to do : http://davidwalsh.name/demo/html5-placeholder.php

推荐答案

我在oracle论坛上找到了这个。

I found this on the oracle forums.

public class TextFieldWithPrompt extends JTextField{

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

    if(getText().isEmpty() && ! (FocusManager.getCurrentKeyboardFocusManager().getFocusOwner() == this)){
        Graphics2D g2 = (Graphics2D)g.create();
        g2.setBackground(Color.gray);
        g2.setFont(getFont().deriveFont(Font.ITALIC));
        g2.drawString("zip", 5, 10); //figure out x, y from font's FontMetrics and size of component.
        g2.dispose();
    }
  }

https://forums.oracle.com/forums/thread.jspa?threadID=1349874

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