Yep, the DG will probably call getItemAt
for every visible row regardless of how many items are actually in the
dataProvider. Multiple calls to length() are simply done as the measurement, layout,
and drawing mechanisms are doing their thing. Same would apply to ComboBox but
obviously there’s less to compute and draw there.
Matt
I hooked up the dataProvider to a ComboBox and the result was more
what I expected. The ComboBox seems to make
0 to length-1 calls to
getItemAt and then stops. The DataGrid seems
to make a fixed number
of calls - perhaps a default grid size?
[Debug] cbTest initialized
[Debug] TestDP(undefined)
[Debug] getItemAt(undefined)
[Debug] get length():5
[Debug] get length():5
[Debug] get length():5
[Debug] get length():5
[Debug] get length():5
[Debug] get length():5
[Debug] get length():5
[Debug] get length():5
[Debug] getItemAt(0)
[Debug] getItemAt(1)
[Debug] getItemAt(2)
[Debug] getItemAt(3)
[Debug] getItemAt(4)
[Debug] get length():5
[Debug] get length():5
[Debug] getItemAt(undefined)
--- In [email protected],
"Matt Chotin" <[EMAIL PROTECTED]> wrote:
> I'd imagine that if you're seeing numerous
calls to length
interspersed
> with getItemAt that we simply didn't do an
optimal loop.
>
>
>
> for (var idx = 0; idx <
dataProvider.length; ++idx)
>
> {
>
> var item = getItemAt(idx);
>
> }
>
>
>
> get length() is going to be called on every
iteration of the loop.
It'd
> obviously be more efficient to store length
in a local variable and
just
> use that, but maybe we didn't somewhere.
>
>
>
> Matt
>
> ________________________________
>
> From: [email protected]
[mailto:[email protected]]
On
> Behalf Of rbelknap
> Sent: Friday, June 03, 2005 3:24 PM
> To: [email protected]
> Subject: [flexcoders] Contract between
DataProvider and ComboBox or
> DataGrid
>
>
>
> Hi,
>
> I'm struggling to figure out the implied
contract between
> DataProviders and their users like ComboBox
or DataGrid. When
either
> a ComboBox or DataGrid first uses a
DataProvider they seem to make
> numerous calls to:
>
> public function get
length():Number
>
> and
>
> function getItemAt(index :
Number)
>
> but it isn't obvious what the logic is behind
these calls.
>
> I was expecting to see a call to get the
length followed by a
series
> of calls to getItemAt starting at index 0 and
running to index
length-
> 1, but that's not what I see.
>
> Has anyone run across any good discussions of
DataProviders and
their
> users?
>
> Thanks,
>
> Randy
>
>
>
>
>
>
> ________________________________
>
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