Javafx 低电平双向绑定

我最近发现了绑定，它们看起来很棒。然而，我无意中发现了一个我想制作的、似乎无法理解的绑定。我有一个textfield，我想以双向方式绑定到double属性。但是，如果字段中的文本可以转换为double，并且它转换为的double在某个范围内，我只希望绑定从字段到double属性。在另一个方向上，我希望绑定不受限制（我也希望能够对int进行绑定，但一旦修复了双精度绑定，这应该很容易）。我相信这必须通过低级别绑定来完成，不是吗？如何做到这一点

我刚开始使用绑定，对它们不是很在行，所以请对我放松点

---

非常感谢。

在JavaFX绑定中，只需添加侦听器并做出相应的反应。如果这样想，您可能会认为侦听器是API的“低级”方面。要想做你想做的事情，你必须创建自己的侦听器。我不知道有什么东西是你想要的“开箱即用”

未准备好“生产使用”的示例：

如果我正确理解您的要求，这将满足您的要求。不过，我相信这段代码可能会导致内存泄漏。理想情况下，您希望侦听器不要阻止另一个被垃圾收集。例如，如果

属性

不再被强引用，则

字段

不应阻止

属性

被GC引用。编辑：根据

ObservableValue

s的实现情况，此代码也可能进入注释中指出的无限更新循环

---

Edit：我给出的第一个“健壮”示例有一些问题，没有提供一种方法来解除属性之间的绑定。我已经修改了示例，使其更加正确，并提供了所述的解除绑定功能。这个新示例基于JavaFX开发人员如何在内部处理双向绑定。

我上面给出的一个更健壮的代码示例。这在很大程度上受到了标准JavaFX内部API使用的代码的“启发”。特别是类

com.sun.javafx.binding.BidirectionalBinding

import javafx.beans.WeakListener;
import javafx.beans.property.DoubleProperty;
import javafx.beans.property.StringProperty;
import javafx.beans.value.ChangeListener;
import javafx.beans.value.ObservableValue;

import java.lang.ref.WeakReference;
import java.util.Objects;

public class CustomBindings {

    // This code is based heavily on how the standard JavaFX API handles bidirectional bindings. Specifically,
    // the class 'com.sun.javafx.binding.BidirectionalBinding'.

    public static void bindBidirectional(StringProperty stringProperty, DoubleProperty doubleProperty) {
        if (stringProperty == null || doubleProperty == null) {
            throw new NullPointerException();
        }
        BidirectionalBinding binding = new BidirectionalBinding(stringProperty, doubleProperty);
        stringProperty.addListener(binding);
        doubleProperty.addListener(binding);
    }

    public static void unbindBidirectional(StringProperty stringProperty, DoubleProperty doubleProperty) {
        if (stringProperty == null || doubleProperty == null) {
            throw new NullPointerException();
        }

        // The equals(Object) method of BidirectionalBinding was overridden to take into
        // account only the properties. This means that the listener will be removed even
        // though it isn't the *same* (==) instance.
        BidirectionalBinding binding = new BidirectionalBinding(stringProperty, doubleProperty);
        stringProperty.removeListener(binding);
        doubleProperty.removeListener(binding);
    }

    private static class BidirectionalBinding implements ChangeListener<Object>, WeakListener {

        private final WeakReference<StringProperty> stringRef;
        private final WeakReference<DoubleProperty> doubleRef;

        // Need to cache it since we can't hold a strong reference
        // to the properties. Also, a changing hash code is never a
        // good idea and it needs to be "insulated" from the fact
        // the properties can be GC'd.
        private final int cachedHashCode;

        private boolean updating;

        private BidirectionalBinding(StringProperty stringProperty, DoubleProperty doubleProperty) {
            stringRef = new WeakReference<>(stringProperty);
            doubleRef = new WeakReference<>(doubleProperty);

            cachedHashCode = Objects.hash(stringProperty, doubleProperty);
        }

        @Override
        public boolean wasGarbageCollected() {
            return stringRef.get() == null || doubleRef.get() == null;
        }

        @Override
        public void changed(ObservableValue<?> observable, Object oldValue, Object newValue) {
            if (!updating) {
                StringProperty stringProperty = stringRef.get();
                DoubleProperty doubleProperty = doubleRef.get();
                if (stringProperty == null || doubleProperty == null) {
                    if (stringProperty != null) {
                        stringProperty.removeListener(this);
                    }
                    if (doubleProperty != null) {
                        doubleProperty.removeListener(this);
                    }
                } else {
                    updating = true;
                    try {
                        if (observable == stringProperty) {
                            updateDoubleProperty(doubleProperty, (String) newValue);
                        } else if (observable == doubleProperty) {
                            updateStringProperty(stringProperty, (Number) newValue);
                        } else {
                            throw new AssertionError("How did we get here?");
                        }
                    } finally {
                        updating = false;
                    }
                }
            }
        }

        private void updateStringProperty(StringProperty property, Number newValue) {
            if (newValue != null) {
                property.set(Double.toString(newValue.doubleValue()));
            } else {
                // set the property to a default value such as 0.0?
                property.set("0.0");
            }
        }

        private void updateDoubleProperty(DoubleProperty property, String newValue) {
            if (newValue != null) {
                try {
                    property.set(Double.parseDouble(newValue));
                } catch (NumberFormatException ignore) {
                    // newValue is not a valid double
                }
            }
        }

        @Override
        public int hashCode() {
            return cachedHashCode;
        }

        @Override
        public boolean equals(Object obj) {
            if (this == obj) {
                return true;
            }

            StringProperty stringProperty1 = stringRef.get();
            DoubleProperty doubleProperty1 = doubleRef.get();

            if (stringProperty1 == null || doubleProperty1 == null) {
                return false;
            }

            if (obj instanceof BidirectionalBinding) {
                BidirectionalBinding other = (BidirectionalBinding) obj;
                StringProperty stringProperty2 = other.stringRef.get();
                DoubleProperty doubleProperty2 = other.doubleRef.get();
                if (stringProperty2 == null || doubleProperty2 == null) {
                    return false;
                }

                return stringProperty1 == stringProperty2 && doubleProperty1 == doubleProperty2;
            }

            return false;
        }

    }

}

导入javafx.beans.WeakListener；
导入javafx.beans.property.DoubleProperty；
导入javafx.beans.property.StringProperty；
导入javafx.beans.value.ChangeListener；
导入javafx.beans.value.observeValue；
导入java.lang.ref.WeakReference；
导入java.util.Objects；
公共类自定义绑定{
//这段代码主要基于标准JavaFXAPI如何处理双向绑定，
//类“com.sun.javafx.binding.BidirectionalBinding”。
公共静态void bindproduction（StringProperty StringProperty、DoubleProperty DoubleProperty）{
如果（stringProperty==null | | doubleProperty==null）{
抛出新的NullPointerException（）；
}
双向绑定绑定=新的双向绑定（stringProperty，doubleProperty）；
stringProperty.addListener（绑定）；
addListener（绑定）；
}
公共静态无效取消绑定双向（StringProperty StringProperty、DoubleProperty DoubleProperty）{
如果（stringProperty==null | | doubleProperty==null）{
抛出新的NullPointerException（）；
}
//双向绑定的equals（Object）方法被重写以考虑
//仅帐户属性。这意味着侦听器将被删除
//虽然它不是*相同的*（==）实例。
双向绑定绑定=新的双向绑定（stringProperty，doubleProperty）；
stringProperty.removeListener（绑定）；
doubleProperty.removeListener（绑定）；
}
私有静态类双向绑定实现ChangeListener、WeakListener{
私有最终WeakReference stringRef；
私人最终WeakReference doubleRef；
//需要缓存它，因为我们无法保存强引用
//此外，更改哈希代码从来都不是一个问题
//好主意，它需要与事实“隔离”
//属性可以是GC'd。
专用最终int cachedHashCode；
私有布尔更新；
私有双向绑定（StringProperty StringProperty、DoubleProperty DoubleProperty）{
stringRef=新的WeakReference（stringProperty）；
doubleRef=新的WeakReference（doubleProperty）；
cachedHashCode=Objects.hash（stringProperty，doubleProperty）；
}
@凌驾
公共布尔值wasGarbageCollected（）{
返回stringRef.get（）==null | | doubleRef.get（）==null；
}
@凌驾
公共无效已更改（可观察值可观察、对象旧值、对象新值）{
如果（！正在更新）{
StringProperty StringProperty=stringRef.get（）；
DoubleProperty DoubleProperty=doubleRef.get（）；
如果（stringProperty==null | | doubleProperty==null）{
if（stringProperty！=null）{
stringProperty.removeListener（此）；
}
if（doubleProperty！=null）{
doubleProperty.removeListener（此）；
}
}否则{
更新=真；
试一试{
if（可观察==stringProperty）{
updateDoubleProperty（doubleProperty，（String）newValue）；
}else if（可观察==doubleProperty）{
updateStringProperty（stringProperty，（Number）newValue）；
}否则{
抛出新的断言错误（“我们是如何来到这里的？”）；
}
}最后{
更新=假；
import javafx.beans.WeakListener;
import javafx.beans.property.DoubleProperty;
import javafx.beans.property.StringProperty;
import javafx.beans.value.ChangeListener;
import javafx.beans.value.ObservableValue;

import java.lang.ref.WeakReference;
import java.util.Objects;

public class CustomBindings {

    // This code is based heavily on how the standard JavaFX API handles bidirectional bindings. Specifically,
    // the class 'com.sun.javafx.binding.BidirectionalBinding'.

    public static void bindBidirectional(StringProperty stringProperty, DoubleProperty doubleProperty) {
        if (stringProperty == null || doubleProperty == null) {
            throw new NullPointerException();
        }
        BidirectionalBinding binding = new BidirectionalBinding(stringProperty, doubleProperty);
        stringProperty.addListener(binding);
        doubleProperty.addListener(binding);
    }

    public static void unbindBidirectional(StringProperty stringProperty, DoubleProperty doubleProperty) {
        if (stringProperty == null || doubleProperty == null) {
            throw new NullPointerException();
        }

        // The equals(Object) method of BidirectionalBinding was overridden to take into
        // account only the properties. This means that the listener will be removed even
        // though it isn't the *same* (==) instance.
        BidirectionalBinding binding = new BidirectionalBinding(stringProperty, doubleProperty);
        stringProperty.removeListener(binding);
        doubleProperty.removeListener(binding);
    }

    private static class BidirectionalBinding implements ChangeListener<Object>, WeakListener {

        private final WeakReference<StringProperty> stringRef;
        private final WeakReference<DoubleProperty> doubleRef;

        // Need to cache it since we can't hold a strong reference
        // to the properties. Also, a changing hash code is never a
        // good idea and it needs to be "insulated" from the fact
        // the properties can be GC'd.
        private final int cachedHashCode;

        private boolean updating;

        private BidirectionalBinding(StringProperty stringProperty, DoubleProperty doubleProperty) {
            stringRef = new WeakReference<>(stringProperty);
            doubleRef = new WeakReference<>(doubleProperty);

            cachedHashCode = Objects.hash(stringProperty, doubleProperty);
        }

        @Override
        public boolean wasGarbageCollected() {
            return stringRef.get() == null || doubleRef.get() == null;
        }

        @Override
        public void changed(ObservableValue<?> observable, Object oldValue, Object newValue) {
            if (!updating) {
                StringProperty stringProperty = stringRef.get();
                DoubleProperty doubleProperty = doubleRef.get();
                if (stringProperty == null || doubleProperty == null) {
                    if (stringProperty != null) {
                        stringProperty.removeListener(this);
                    }
                    if (doubleProperty != null) {
                        doubleProperty.removeListener(this);
                    }
                } else {
                    updating = true;
                    try {
                        if (observable == stringProperty) {
                            updateDoubleProperty(doubleProperty, (String) newValue);
                        } else if (observable == doubleProperty) {
                            updateStringProperty(stringProperty, (Number) newValue);
                        } else {
                            throw new AssertionError("How did we get here?");
                        }
                    } finally {
                        updating = false;
                    }
                }
            }
        }

        private void updateStringProperty(StringProperty property, Number newValue) {
            if (newValue != null) {
                property.set(Double.toString(newValue.doubleValue()));
            } else {
                // set the property to a default value such as 0.0?
                property.set("0.0");
            }
        }

        private void updateDoubleProperty(DoubleProperty property, String newValue) {
            if (newValue != null) {
                try {
                    property.set(Double.parseDouble(newValue));
                } catch (NumberFormatException ignore) {
                    // newValue is not a valid double
                }
            }
        }

        @Override
        public int hashCode() {
            return cachedHashCode;
        }

        @Override
        public boolean equals(Object obj) {
            if (this == obj) {
                return true;
            }

            StringProperty stringProperty1 = stringRef.get();
            DoubleProperty doubleProperty1 = doubleRef.get();

            if (stringProperty1 == null || doubleProperty1 == null) {
                return false;
            }

            if (obj instanceof BidirectionalBinding) {
                BidirectionalBinding other = (BidirectionalBinding) obj;
                StringProperty stringProperty2 = other.stringRef.get();
                DoubleProperty doubleProperty2 = other.doubleRef.get();
                if (stringProperty2 == null || doubleProperty2 == null) {
                    return false;
                }

                return stringProperty1 == stringProperty2 && doubleProperty1 == doubleProperty2;
            }

            return false;
        }

    }

}