Re: Destroy a widget

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Benjamin Possolo

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Oct 29, 2012, 4:43:41 PM10/29/12
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I presume by uibinder owner you mean your HelloWorld class overrides the onEvent() method, is that correct?

I also presume that you have some other component that is using the HelloWorld objects and attaching them to the view.
For example, in your EntryPoint:

HelloWorld h1 = new HelloWorld();
HelloWorld h2 = new HelloWorld();

FlowPanel panel = new FlowPanel();
panel.add(h1);
panel.add(h2);

GWT.getRoot().add(panel);

If you want to "destroy" h1, and have it stop reacting to events, simply remove it from the dom and ensure it is garbage collected (ie. set your reference to null):

panel.remove(h1);
h1 = null;

Benjamin Possolo

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Oct 29, 2012, 4:46:02 PM10/29/12
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Sorry there is a typo there.

GWT.getRoot().add(panel);
should be
RootPanel.get().add(panel);

Jens

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Oct 29, 2012, 4:46:34 PM10/29/12
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When you create two HelloWorld widgets each of them receives its own events. If you use @UiHandler in your UiBinder widget and you want to stop receive events for a widget without removing the widget itself from the parent (for whatever reason) you have to "disable" your @UiHandler implementation.

So you would end up having

@UiHandler(...)
void onEvent(...) {
  if(handleEvents) {
     //do your event logic
  }
}

or you use a Delegate interface that a class can implement and that contains your event logic implementation:

@UiHandler(...)
void onEvent(...) {
  if(delegate != null) {
     delegate.onEvent();
  }
}

In that case you would disable your events by nulling your delegate: widget.setDelegate(null)


Otherwise you have to remove the widget from the parent.


-- J.

Jose María Zaragoza

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Oct 30, 2012, 7:58:34 AM10/30/12
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If you want to "destroy" h1, and have it stop reacting to events, simply remove it from the dom and ensure it is garbage collected (ie. set your reference to null):

panel.remove(h1);
h1 = null;

Thanks

Garbage collected? I thought that we were in a Javascript world
Setting to null doesn't work like I want because it's Javascript code.

And I don't want to remove it from a panel , but "destroy it" as entity. Maybe that doesn't have any sense, because I don't know how is implemented by GWT compiler into Javascript code, but  h1=null doesn`t work for me



Jose María Zaragoza

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Oct 30, 2012, 8:00:48 AM10/30/12
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Thanks for you answer. 
But  "to remove the widget from the parent." doesn`t avoid to receive events ( or my tests were wrong )

Benjamin Possolo

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Oct 31, 2012, 5:15:30 PM10/31/12
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I can't really understand what you are asking or saying.

If you want the widget to remain visible but to stop receiving events, do what Jens said: suppress the event handling logic in the event handler.
If you want the widget to stop being visible and to stop receiving events, just do what I said: remove the widget from it's container.

and yes, javascript also has garbage collection otherwise every web application would be one giant memory leak
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