This API can be used to for example allow the creation of Dialogs that donot require the use of a Stage (which itself has the showAndWait() method that makes use of this API).  Stages are not always desirable for this.  Alternatively, a special Pane could be created that offers a showAndWait() style method, but that may limit potential other uses of nested event loops.

The API looks intuitive enough as it is currently, and could be moved as-is to Platform in the future.

Below part of the mailinglist discussion:

---------------

Hi John,

Please file an RFE to introduce this public API.

-- 
best regards,
Anthony

On 11/13/2013 08:35 PM, John Hendrikx wrote:
> On 13/11/2013 16:35, Stephen F Northover wrote:
>> What is the difference?
>>
>> Dialog d = new Dialog() {
>>    public void onClose() {
>>       Platform.exitNestedEventLoop();
>>    }
>> }
>> Platform.enterNestedEventLoop();
> I find the current API to work well, it is just in the wrong package
> tree
>
> Considering I didn't know about nested event loops before, I find the
> solution quite elegant -- leave the old event loop on the call stack,
> and start a fresh one that can be exited to continue again where the
> main event loop was halted -- it's almost like a 2nd thread gets
> started, but there isn't
>
> --John
>
>>
>> Steve
>>
>> On 2013-11-13 5:28 AM, Tom Schindl wrote:
>>> What bothers me with the API as it is today is that I have call
>>> enter/exit, I would find it more easy to work with an API like:
>>>
>>> -------8<-------
>>> WaitCondition c = new WaitCondition();
>>> Dialog d = new Dialog() {
>>>     public void onClose() {
>>>        c.release();
>>>     }
>>> }
>>> Platform.spinNestedEventLoop(c);
>>> ------->8-------
>>>
>>> Tom
>>>
>>> On 13.11.13 11:18, Artem Ananiev wrote:
>>>> I also think it's a good request for public API. In AWT/Swing, people
>>>> had been using ugly workarounds with modal dialogs just to enter a
>>>> nested event loop, until public java.awt API was finally provided:
>>>>
>>>> http://docs.oracle.com/javase/7/docs/api/java/awt/SecondaryLoop.html
>>>>
>>>> http://docs.oracle.com/javase/7/docs/api/java/awt/EventQueue.html#createSecondaryLoop()
>>>>
>>>>
>>>>
>>>> The same is here in JavaFX: unless Toolkit.enter/exitNestedEventLoop()
>>>> is exposed at javafx.* level, people will have to workaround it by
>>>> using
>>>> Stage, or calling into com.sun.javafx.*, which is not good.
>>>>
>>>> Thanks,
>>>>
>>>> Artem
>>>>
>>>> On 11/13/2013 10:15 AM, John Hendrikx wrote:
>>>>> Hi List,
>>>>>
>>>>> Any chance that Toolkit.getToolkit().enterNestedEventLoop() will in
>>>>> the
>>>>> future become public API?
>>>>>
>>>>> I'm currently using this to create Dialogs based on a Pane to avoid
>>>>> creating Stages (which have the nice show and showAndWait
>>>>> functionality).  I duplicated this functionality in a Pane,
>>>>> allowing me
>>>>> to create Dialogs on top of existing Scenes without creating a Stage,
>>>>> and it makes use of the enterNestedEventLoop and exitNestedEventLoop
>>>>> functions in com.sun.javafx.tk.Toolkit.
>>>>>
>>>>> The reason I'm avoiding the Stages is because they donot play well
>>>>> with
>>>>> an application that never has the mouse or keyboard focus (my
>>>>> application is fully remote controlled) -- creating a Stage, even
>>>>> one to
>>>>> just show a Dialog, will cause Windows to try and attract the user's
>>>>> attention by flashing its taskbar button (for which I filed a
>>>>> bug/feature request) and this is undesired.
>>>>>
>>>>> Regards,
>>>>> John
>>>>>
>>>>> (Here's a part of the DialogPane to show and close it:)
>>>>>
>>>>>     public R showDialog(Scene scene, boolean synchronous) {
>>>>>       this.synchronous = synchronous;
>>>>>       this.scene = scene;
>>>>>       this.oldFocusOwner = scene.getFocusOwner();
>>>>>
>>>>>       Parent root = scene.getRoot();
>>>>>
>>>>>       stackPane.getChildren().add(root);
>>>>>       stackPane.getChildren().add(this);
>>>>>
>>>>>       scene.setRoot(stackPane);
>>>>>
>>>>>       requestFocus();
>>>>>
>>>>>       if(synchronous) {
>>>>>         return (R)Toolkit.getToolkit().enterNestedEventLoop(this);
>>>>>       }
>>>>>
>>>>>       return null;
>>>>>     }
>>>>>
>>>>>     public void close() {
>>>>>       Parent originalRoot = (Parent)stackPane.getChildren().remove(0);
>>>>>
>>>>>       scene.setRoot(originalRoot);
>>>>>       scene = null;
>>>>>
>>>>>       if(oldFocusOwner != null) {
>>>>>         oldFocusOwner.requestFocus();
>>>>>       }
>>>>>
>>>>>       if(synchronous) {
>>>>>         Toolkit.getToolkit().exitNestedEventLoop(this, getResult());
>>>>>       }
>>>>>     }
>>>>>
>>>>>
>>
>