绑定到整数属性的文本字段变为空时的NPE

Question

我将文本字段绑定到整数属性：

@FXML
public TextField countMin;

...

// Limits is my model - countMin is an `IntegerProperty`.
countMin.textProperty().bindBidirectional(limits.countMin, new NumberStringConverter(new LimitFormat()));

Limits是数据模型。

public class Limits {
  // Logger.
  protected static final Logger log = LoggerFactory.getLogger(Limits.class);
  // The properties.
  IntegerProperty countMin = new SimpleIntegerProperty(LimitFormat.NoValue);
...

LimitFormat看起来像这样 - 它试图将TextField中的空字符串转换为NoValue中的特殊IntegerProperty数字。我不认为这是在空案件中调用的，但这里是为了完整性。

public class LimitFormat extends DecimalFormat {
  // Special NoValue value.
  public static final Integer NoValue = Integer.MAX_VALUE;
  // Standard numbers in all other cases.
  private static final String limitFormat = "#";

  public LimitFormat() {
    super(limitFormat);
  }

  @Override
  public StringBuffer format(double number, StringBuffer toAppendTo, FieldPosition pos) {
    // NoValue becomes empty string.
    return ((int) number) == NoValue ? toAppendTo : super.format(number, toAppendTo, pos);
  }

  @Override
  public StringBuffer format(long number, StringBuffer toAppendTo, FieldPosition pos) {
    // NoValue becomes empty string.
    return number == NoValue ? toAppendTo : super.format(number, toAppendTo, pos);
  }

  @Override
  public Number parse(String source, ParsePosition parsePosition) {
    // Empty string  should become NoValue.
    return source == null || source.isEmpty() ? NoValue : super.parse(source, parsePosition);
  }

}

几乎在所有情况下它都可以正常工作，但是当文本字段为空时它似乎被绕过了。

Stack看起来像：

INFO    Attempt to set integer property to null, using default value instead.
INFO    java.lang.NullPointerException
    at javafx.beans.property.IntegerProperty.setValue(IntegerProperty.java:66)
    at javafx.beans.property.IntegerPropertyBase.setValue(IntegerPropertyBase.java:52)
    at com.sun.javafx.binding.BidirectionalBinding$StringConversionBidirectionalBinding.changed(BidirectionalBinding.java:669)
    at com.sun.javafx.binding.ExpressionHelper$Generic.fireValueChangedEvent(ExpressionHelper.java:347)
    at com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(ExpressionHelper.java:80)
    at javafx.scene.control.TextInputControl$TextProperty.fireValueChangedEvent(TextInputControl.java:1116)
    at javafx.scene.control.TextInputControl$TextProperty.markInvalid(TextInputControl.java:1120)
    at javafx.scene.control.TextInputControl$TextProperty.invalidate(TextInputControl.java:1060)
    at javafx.scene.control.TextInputControl$TextProperty.access$200(TextInputControl.java:1032)
    at javafx.scene.control.TextInputControl$1.invalidated(TextInputControl.java:130)
    at com.sun.javafx.binding.ExpressionHelper$SingleInvalidation.fireValueChangedEvent(ExpressionHelper.java:135)
    at com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(ExpressionHelper.java:80)
    at javafx.scene.control.TextField$TextFieldContent.delete(TextField.java:91)
    at javafx.scene.control.TextInputControl.replaceText(TextInputControl.java:463)
    at javafx.scene.control.TextInputControl.deleteText(TextInputControl.java:417)
    at javafx.scene.control.TextInputControl.deletePreviousChar(TextInputControl.java:771)
    at com.sun.javafx.scene.control.skin.TextFieldSkin.deleteChar(TextFieldSkin.java:593)
    at com.sun.javafx.scene.control.behavior.TextFieldBehavior.deleteChar(TextFieldBehavior.java:195)
    at com.sun.javafx.scene.control.behavior.TextInputControlBehavior.deletePreviousChar(TextInputControlBehavior.java:343)
    at com.sun.javafx.scene.control.behavior.TextInputControlBehavior.callAction(TextInputControlBehavior.java:152)
    at com.sun.javafx.scene.control.behavior.BehaviorBase.callActionForEvent(BehaviorBase.java:222)
...