I stumbled upon this very interesting old topic today, when I tried to
manipulate the *display* property of the container's element. I'm gonna
demonstrate here, that this issue has few hard to deal with pitfalls.
So, the first stumbling block I ran into, was a vain attempt to change the
*display* property. This call
myLayoutPanel.getWidgetContainerElement(myWidget).getStyle().setDisplay(
Display.NONE);
in fact doesn't do anything. I started to dig inside the code and found
these lines within *com.google.gwt.layout.client.LayoutImpl::layout(Layer
layer)*:
if (layer.visible) {
style.clearDisplay();
} else {
style.setDisplay(Display.NONE);
}
Obviously field *visible* is set to *true* for all children's layers of
*LayoutPanel*. Now, the public inner class
*com.google.gwt.layout.client.Layout$Layer* has in fact a setter for flag
*visible*:
/**
* Sets the layer's visibility.
*
* @param visible
*/
public void setVisible(boolean visible) {
this.visible = visible;
}
The problem is though, that *LayoutPanel* doesn't give you a layer for its
widgets, since the accessor method is private:
private Layout.Layer getLayer(Widget child) {
assert child.getParent() == this : "The requested widget is not a child
of this panel";
return (Layout.Layer) child.getLayoutData();
}
However, any *Widget* object has a public accessor for its own layout as:
/**
* Gets the panel-defined layout data associated with this widget.
*
* @return the widget's layout data
* @see #setLayoutData
*/
public Object getLayoutData() {
return layoutData;
}
Now, whenever I want to change the display property of any widget within a
*LayoutPanel* I can simply write:
Layout.Layer layer = (Layout.Layer) myWidgetInsideLayoutPanel.getLayoutData
();
layer.setVisible(false);
and it actually works fine.
The question is though, how safe are these calls? We get an *Object* and do
an unsafe cast, assuming that it is in fact *Layout.Layer*. However my
concern is, that I assume the lib gwt code to have such straight casts
simply due to the fact, that it is an implementation detail, which is of
cause a subject of potential future changes.
We might assume that as a workaround one can change the *visibility*
property of the container's widget instead. But again, there's no
guarantee, that this parameter won't be added to *Layout$Layer* and managed
by *LayoutImpl* just like the *display* property. All in all, I feel that
my hands are tied.
On Thursday, June 10, 2010 at 3:54:21 PM UTC+3, Stefan Bachert wrote:
>
> Hi Chris,
>
> it is not really clear to me.
> Did you switched of the added child, or the layer (div) containing the
> added child.
> The first is not suffient and will leave the layer (div).
>
> I think, the correct method to get the layer div of any child widgets
> is
> getWidgetContainerElement.
>
> Call this and set the visibiltity
>
> Stefan Bachert
> http://gwtworld.de
>
>
> On Jun 9, 11:28 pm, Chris <[email protected]> wrote:
> > Hi there
> >
> > I'm trying to hide a layer in my LayoutPanel. The idea is to have a
> > layer act a bit like a popup, but it's not really a popup, and it
> > makes it easier if it is a layer.
> >
> > I'm trying to hide it, so I toggle the layer child (a simplePanel)'s
> > visibility property on/off, which seems to work fine, but it leaves a
> > div element (from the layer I suppose), which means I can't click
> > through to the elements behind it... When I look at the DOM, I get a
> > <div> with all the properties from my layer, and then the <div> inside
> > that is the SimplePanel I'm using.
> >
> > Any ideas? I guess i could just ask for the widget's parent? But that
> > seems hacky. Am I doing something wrong?
> >
> > Chris
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