java JTextField：更改前景色并保存内容
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JTextField: Change the foreground color and save the content
提问by user2144555
I have a frame with some JTextFieldsfor the user insert some values.
When the window is opened, the text fields have written, in gray, what the user should write in that container, like "value in seconds"...
我有一个框架，其中有一些JTextFields供用户插入一些值。当窗口打开时，文本字段以灰色写入用户应该在该容器中写入的内容，例如“以秒为单位的值”...
I want to change the color of those letters (I think it is the foreground) to dark when the user starts to write in the JTextFields, and save to a Stringwhat is written by the user.
我想这些信（我觉得是前景）的颜色改为深色，当用户开始写的JTextFields，并保存到String什么是由用户编写。
回答by Daniel Lerps
For the colour change you have to implement a FocusListenerwhich sets the foreground with setForeground(). If you want to have a String of the current content of the JTextFieldyou can achieve this with a DocumentListenerto the underlying Document.
对于颜色更改，您必须实现一个FocusListener设置前景的setForeground(). 如果你想拥有一个当前内容的字符串，JTextField你可以使用DocumentListener底层的Document.
See this code as an example (I use blue and red for the colour and store the Text value of tfin the Stringcontent):
请参阅此代码作为示例（我使用蓝色和红色作为颜色并将文本值存储tf在String内容中）：
JTextField tf = new JTextFiedl();
tf.addFocusListener(new FocusListener()
{
@Override
public void focusGained(FocusEvent fe)
{
tf.setForeground(INACTIVE_COLOUR);
}
@Override
public void focusLost(FocusEvent fe)
{
tf.setForeground(ACTIVE_COLOUR);
}
});
A full working example is here:
一个完整的工作示例在这里：
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class TF
{
private final Color ACTIVE_COLOUR = Color.BLUE;
private final Color INACTIVE_COLOUR = Color.RED;
private String content; //text of the text field is stored here
private JTextField tf;
private JTextField lbl;
public TF()
{
JFrame mainFrame = new JFrame("Window");
tf = new JTextField("Hint");
lbl = new JTextField("click here to change focus");
tf.setForeground(ACTIVE_COLOUR);
setListeners();
mainFrame.add(tf, BorderLayout.NORTH);
mainFrame.add(lbl, BorderLayout.SOUTH);
mainFrame.pack();
mainFrame.setVisible(true);
}
private void setListeners()
{
tf.addFocusListener(new FocusListener()
{
@Override
public void focusGained(FocusEvent fe)
{
tf.setForeground(INACTIVE_COLOUR);
}
@Override
public void focusLost(FocusEvent fe)
{
tf.setForeground(ACTIVE_COLOUR);
}
});
tf.getDocument().addDocumentListener(new DocumentListener()
{
@Override
public void removeUpdate(DocumentEvent de)
{
content = tf.getText();
}
@Override
public void insertUpdate(DocumentEvent de)
{
content = tf.getText();
}
@Override
public void changedUpdate(DocumentEvent de)
{
content = tf.getText();
}
});
}
public static void main(String[] args)
{
TF tf = new TF();
}
}
回答by camickr
See Text Promptfor another approach.
另一种方法请参见文本提示。
