带有JFormattedTextField的KeyListener

Question

有人可以向我解释为什么getValue()函数总是返回null ？ 如果我使用getText()而不是getValue()那么一切都很完美，但我想要的是价值而不是文本。 我可以将它转换为整数，但我不认为这是最好的方法。

public class Test {    
    public static void main(String[] args) {

        JFrame jf = new JFrame("test jftf"); 
        jf.setSize(100, 100);
        jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
        jf.setVisible(true); 
        JFormattedTextField jftf = new JFormattedTextField(NumberFormat.getIntegerInstance()); 
        jftf.addKeyListener(new KeyListener() {
            @Override
            public void keyTyped(KeyEvent e) {
            }

            @Override
            public void keyPressed(KeyEvent e) {
            }

            @Override
            public void keyReleased(KeyEvent e) {
                System.out.println(jftf.getValue()); 
            }

        });
        jf.add(jftf); 
    }

}

Answer 1

如果您依赖于getValue()方法，则需要确保已提交当前编辑。 您可以通过调用方法commitEdit()来执行此操作，否则您可能无法获得您期望的值：

@Override
public void keyReleased(KeyEvent e) {
    //Forces the current value to be taken from the AbstractFormatter 
    //and set as the current value:
    try {
        jftf.commitEdit();
    } catch (ParseException e1) {
        //Handle possible parsing error...
    }
    System.out.println(jftf.getValue()); 
}

Answer 2

这是一个示例，说明这是如何工作的值的名称不准确。 想想这样。 JFormattedTextField有一个名为lastValidInt的字段，它包含一个整数。 每次格式化字段中的文本时，程序将检查字段中的文本是否为数字。 如果是，那么lastValidInt将被设置为该字符串。

getValue()方法将检查lastValidInt是否已初始化，如果已经初始化，则返回lastValidInt的值。 如果没有则返回null 。

示例：这些假设您每次都在重新启动应用程序。 输入是您将在该字段中编写的内容。 输出是控制台在输入内容后打印的内容。

1:
Input: a
Ouput: null
//a is not a number therefore the output is null

2:
Input:  1
Output: 1
//1 is a number therefore the output is 1

3:
Input1: a
Ouput: null
Input2: as
Ouput: null
Input3: asd
Ouput: null
Input4: asdf
Ouput: null
//a is not a number therefore the output is null

4:
Input1: 1
Ouput: 1
Input2: 1f
Ouput: 1
//The first thing the was read here was 1 therefore lastValidInt was set to 1 then the next input is 1f which is not a number therefore lastValidInt remained 1

5:
Input1: f
Ouput: null
Input2: f1
Ouput: null
//f is not a number therefore output is null, f1 is not a number either since it has a character that is not a digit and therefore lastValidInt has not been initialized

6:
Input1: f
Ouput: null
Input2: 
Output: null
Input3: 1
Output: 1
Input4: 1f
Output: 1
//f is not a number therefore output is null, "" is also not a number therefore output is null again then the only thing that exists in the field is 1 which is a number therefore output is 1, finally by adding a f the field is no longer a number so output is same as before.

7:
Input1: f
Ouput: null
Input2: 1f (moved back to the begining without erasing f)
Output: null
//f is not a number therefore output is null, 1f is not a number either since it has a character that is not a digit and therefore lastValidInt has not been initialized