Re: CellTree question about varying cell composition

Thank you, that sounds like something worth trying.

On Apr 9, 4:24 am, Thomas Broyer <t.bro...@gmail.com> wrote:
> On Sunday, April 3, 2011 5:52:41 AM UTC+2, tomInNewEngland wrote:
>
> > Hi All:
>
> > I have a CellTree and I want to use two different cells for the leaf
> > and branch nodes.  The leaf nodes are all to have a checkbox and the
> > brances are not.  Leaves and branches appear on the same levels.
>
> > I constructed a CompositeCell out of a CheckboxCell and a homegrown
> > cell (based on AbstractCell<T>), and I put a test in the
> > CompositeCell.render() method, that looked something like this:
>
> > if (cell instanceof CheckboxCell) {
> >   if (value.isLeaf()) {
> >     cell.render(context, hasCell.getValue(value), sb);
> >   }
> > }
>
> > With this code, the checkbox cell wasn't rendered at all for the
> > branch nodes.  This appeared to work at first, but selecting a branch
> > node would give me an error that seemed to be at the Javascript
> > level.  It read: "(Typeerror) elem is null".  None of my code was
> > identified in the stack trace, so I don't get what was wrong.
>
> IIRC, CompositeCell assumes all of its composited cells are rendered, so it
> assumes it has as many child nodes as composited cells.
>
> > Can someone suggest what that error might have meant, or better,
> > suggest the right way to go about designing a cell that's different
> > for leaf and branch nodes that might be siblings in the CellTree.
>
> Maybe put the logic of displaying the checkbox down to the CheckboxCell
> (extend and override render() to either render the checkbox or a
> SafeHtmlUtils.EMPTY_SAFE_HTML).
> Either that, or make your own "CompositeCell-like" cell.
>
> > Another question: when designing a cell to use, what is the right way
> > to test the values that will be displayed in that cell?  Besides
> > including the checkbox or not, I'd like to vary the look based on
> > other parameters.
>
> I'd follow the new Appearance-based approach; this allows you to mock an
> Appearance for the tests.
> Seehttps://groups.google.com/d/topic/google-web-toolkit-contributors/Scl...
> andhttp://code.google.com/p/google-web-toolkit/source/detail?r=9879
> I haven't tried it though.
>
> You could also, more simply, base your rendering on a SafeHtmlTemplates and
> mock it for the tests, checking which template method is called, with which
> arguments, depending on the value.

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