endless loop on property sync code

[Tom Eugelink]

http://javafx-jira.kenai.com/browse/RT-18963


On 2012-01-17 17:07, Richard Bair wrote:
> I would have thought so. WIth an InvalidationListener we cannot make this check, because we don't actually know what the new value is unless we ask for the new value -- which would make everything eager. But for a change event we should only actually send a change event notification if it has actually changed. Sounds like a bug.
>
> Richard
>
> On Jan 17, 2012, at 5:35 AM, Tom Eugelink wrote:
>
>> In an attempt to make some code "cheaper" I decided it could be a good idea to redundantly store the index next to the value it pointed to. Since this could save a fairly costly "getIndex" call.
>>
>> So I ended up with two properties; one public value and one private index. Basically both denote the same value, so I needed to add sychronisation code:
>>
>>         // react to changes of the value
>>         this.valueObjectProperty.addListener(new ChangeListener<T>()
>>         {
>>             @Override
>>             public void changed(ObservableValue<? extends T>  property, T oldValue, T newValue)
>>             {
>>                 // get the value of the new index
>>                 Object lIdx = getDataProvider().getIndex(newValue);
>>                 if (lIdx == null) throw new IllegalArgumentException("Value does not exist " + newValue);
>>
>>                 // set the value
>>                 indexObjectProperty.setValue(lIdx);
>>             }
>>         });
>>
>>         // react to changes of the index
>>         this.indexObjectProperty.addListener(new ChangeListener<Object>()
>>         {
>>             @Override
>>             public void changed(ObservableValue<? extends Object>  property, Object oldIndex, Object newIndex)
>>             {
>>                 // get the value of the new index
>>                 T lValue = (T)getDataProvider().getValue(newIndex);
>>
>>                 // set the value
>>                 valueObjectProperty.setValue(lValue);
>>             }
>>         });
>>
>>
>> This code results in an endless loop:
>> Exception in Application start method
>> Exception in thread "main" java.lang.RuntimeException: Exception in Application start method
>>     at com.sun.javafx.application.LauncherImpl.launchApplication1(Unknown Source)
>>     at com.sun.javafx.application.LauncherImpl.access$000(Unknown Source)
>>     at com.sun.javafx.application.LauncherImpl$1.run(Unknown Source)
>>     at java.lang.Thread.run(Thread.java:662)
>> Caused by: java.lang.StackOverflowError
>>     at com.sun.javafx.binding.ExpressionHelper$SingleChange.fireValueChangedEvent(Unknown Source)
>>     at com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(Unknown Source)
>>     at javafx.beans.property.ObjectPropertyBase.fireValueChangedEvent(Unknown Source)
>>     at javafx.beans.property.ObjectPropertyBase.markInvalid(Unknown Source)
>>     at javafx.beans.property.ObjectPropertyBase.set(Unknown Source)
>>     at javafx.beans.property.ObjectProperty.setValue(Unknown Source)
>>     at jfxtras.scene.control.SpinnerX$1.changed(SpinnerX.java:147)
>>     at com.sun.javafx.binding.ExpressionHelper$SingleChange.fireValueChangedEvent(Unknown Source)
>>     at com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(Unknown Source)
>>     at javafx.beans.property.ObjectPropertyBase.fireValueChangedEvent(Unknown Source)
>>     at javafx.beans.property.ObjectPropertyBase.markInvalid(Unknown Source)
>>     at javafx.beans.property.ObjectPropertyBase.set(Unknown Source)
>>     at javafx.beans.property.ObjectProperty.setValue(Unknown Source)
>>     at jfxtras.scene.control.SpinnerX$2.changed(SpinnerX.java:167)
>>     at com.sun.javafx.binding.ExpressionHelper$SingleChange.fireValueChangedEvent(Unknown Source)
>>     at com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(Unknown Source)
>>     at javafx.beans.property.ObjectPropertyBase.fireValueChangedEvent(Unknown Source)
>>     at javafx.beans.property.ObjectPropertyBase.markInvalid(Unknown Source)
>> ...
>>
>>
>> To solve this, I have to explicitly check if the value changed before the setValue (see "equals" below). Isn't Property suppose to do this?
>>
>>         // react to changes of the value
>>         this.valueObjectProperty.addListener(new ChangeListener<T>()
>>         {
>>             @Override
>>             public void changed(ObservableValue<? extends T>  property, T oldValue, T newValue)
>>             {
>>                 // get the value of the new index
>>                 Object lIdx = getDataProvider().getIndex(newValue);
>>                 if (lIdx == null) throw new IllegalArgumentException("Value does not exist " + newValue);
>>
>>                 // set the value
>>                 if (SpinnerX.equals(indexObjectProperty.getValue(), lIdx) == false)
>>                 {
>>                     indexObjectProperty.setValue(lIdx);
>>                 }
>>             }
>>         });
>>
>>         // react to changes of the index
>>         this.indexObjectProperty.addListener(new ChangeListener<Object>()
>>         {
>>             @Override
>>             public void changed(ObservableValue<? extends Object>  property, Object oldIndex, Object newIndex)
>>             {
>>                 // get the value of the new index
>>                 T lValue = (T)getDataProvider().getValue(newIndex);
>>
>>                 // set the value
>>                 if (SpinnerX.equals(valueObjectProperty.getValue(), lValue) == false)
>>                 {
>>                     valueObjectProperty.setValue(lValue);
>>                 }
>>             }
>>         });
>>
>>
>