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Detailed review of 3.18.2. The datagrid element

From: Mihai Sucan <mihai.sucan@gmail.com>
Date: Tue, 11 Sep 2007 21:34:06 +0300
To: public-html <public-html@w3.org>
Message-ID: <op.tyh5u4p2mcpsjgr0b0dp@athlon>

Hello!

I have reviewed section 3.18.2. "The datagrid element" [1] from the HTML 5  
specification. I have the following comments to make:


1. In the section 3.18.2.4.1. "Common default data provider method  
definitions for cells" [2]:

Editable cells are defined such that "if the first element child of a  
cell's element is an input element that has a type attribute with the  
value text or that has no type attribute at all, then the cell acts as an  
editable cell."

That's fine, however, it does ommit other important editable input types:  
password, email, and url.

There are other editable input types, yet, I am not sure if these should  
also be included: datetime, datetime-local, date, month, week, time,  
number, and range.



2. I'm being "picky"  about the language/wording again. In section  
3.18.2.5. "Populating the datagrid element" [3] one can read:

"... the element must fire a single load event at itself ..."

"The datagrid must then populate itself ..."

"... the datagrid must invoke the initialize() method ... "

The provided quotes share something in common: the datagrid does  
everything. The datagrid fires events, the datagrid populates itself, the  
datagrid invokes methods. Does it really do that? :)

I would suggest changing the "perspective": it's the UA that invokes  
methods, that fires appropriate events, etc.

I provided only 3 quotes, but the section has more of these.

The quote which made me notice this problem was:

"To obtain data from the data provider, the element must invoke methods on  
the data provider object in the following ways:"

First thing that came into my mind: "heh, whattf.org?? That's a weird  
element." :)

Point is, some of the sentences are really weird.



3. In the same section [3] one can read:

"To establish how the type of a cell"

That's obviously wrong. Maybe that should be:

"To establish the cell type"



4. Again, in the same section [3], one can read:

"Examine the classes that apply to the cell. If the progress class applies  
to the cell, it is a progress bar. Otherwise, if the cyclable class  
applies to the cell, it is a cycling cell whose value can be cycled  
between multiple states. Otherwise, none of these classes apply, and the  
cell is a simple text cell."

Given the nature of classes, there might be "progress" and "cyclable".  
What should the UA do then?



5. Reading 3.18.2.7. "Requirements for interactive user agents" [4] I  
found this:

"If a cell is a cell whose value can be cycled between multiple states,  
then the user must be able to activate the cell to cycle its value. When  
the user activates this "cycling" behaviour of a cell, then the datagrid  
must invoke the data provider's cycleCell() method, with a  
RowSpecification object representing the cell's row as the first argument  
and the cell's column index as the second. The datagrid must act as if the  
datagrid's updateCellChanged() method had been invoked with those same  
arguments immediately *before* the provider's method was invoked."

Why invoke updateCellChanged() before cycleCell()?

 From the definition of cycleCell() [5]:

"Called by the datagrid when the user changes the state of a cyclable cell  
on row row, column column. The data provider should change the state of  
the cell to the new state, as appropriate. There is no need to tell the  
datagrid that the cell has changed, as the datagrid automatically assumes  
that the given cell will need updating."

The last phrase is important: the datagrid automatically assumes that the  
given cell *will* need updating - no need to tell the datagrid the cell  
changed.

So, again, why *before*?

Datagrid's updateCellChanged() method must be invoked with the same  
arguments immediately *after* the data provider's cycleCell() method is  
invoked.

The same "error" is made when defining editable cells and cells with a  
checkbox. Maybe I'm not understanding something?

Yet... in the section 3.18.2.9. "Columns and captions" [6] one can read:

"If a column is sortable, then the user must be able to invoke it to sort  
the data. When the user does so, then the datagrid must invoke the data  
provider's toggleColumnSortState() method, with the column's index as the  
only argument. The datagrid must *then* act as if the datagrid's  
updateEverything() method had been invoked."

The keyword is *then*, which means the updateEverything() method is  
invoked after the toggleColumnSortState() runs - as I would expect.

So, I might not be wrong.



6. "Big Issue: One possible thing to be added is a way to detect when a  
row/selection has been deleted, activated, etc, by the user (delete key,  
enter key, etc)."

Obviously this is needed. Maybe this would be best solved with some new  
events fired on the datagrid element. I would suggest not to add any  
method to the DataGridDataProvider which would be called for a specific  
event. E.g. don't define a new method like DataGridDataProvider.onAdd(),  
but instead make it an event "add". The event should include several  
properties: a reference to the datagrid element, the new row, etc.

The reason I am suggesting the definition of new events is that one would  
not need to define his/her own DataGridDataProvider if the default one is  
good enough for his/her initial purpose - coupled with a few event  
listeners.



7. I would like to know if the author can call the methods from the  
default DataGridDataProvider?

It seems datagrid.data is null by default, thus you cannot call, say,  
datagrid.data.getRowCount(row). However, if one defines his/her own  
DataGridDataProvider object, then calling datagrid.data.getRowCount(row)  
would work.

I was thinking: why not define datagrid.data such that it holds by default  
all the methods as callable read-only native functions - one cannot  
overwrite them individually, just the entire DataGridDataProvider object.  
Would this be workable?

This would be needed by scripts in applications that do not need to  
overwrite the native object, yet need to get the row count, or get the  
column count, etc.



8. Continuing within a similar line of thought, the DataGridDataProvider  
object should also include getRow(r) and getCell(r, c), to get the r-th  
row element, and c-th cell element from the r-th row.

The datagrid is similar in concept with a table element. It would need  
some methods to add/find/delete rows and columns - similar to the provided  
methods on the table element.

These methods would not be needed in cases when a <table> is used as the  
data provider for the datagrid. Yet, in the other cases (for selects,   
datalists, and h1-h6, LIs, etc) ... this set of methods would be a welcome  
addition.



9. I would have a general comment on this element: it's too complex,  
trying to do it all. "Simple" concepts as the <table> element ended up  
being quite very complex implementation-wise, specially when used wrongly  
(e.g. tables used for layouts). Perhaps the spec leaves a lot of "dark  
holes" noticeable only when one starts to implement this element, and when  
authors start putting the element into real usage. Probably there are lots  
of places where UA implementations can differ.

What I find that opens lots of "back-doors" is the content model itself,  
allowing: select elements, datalist elements, table elements, and headings  
(h1-h6) with list items included. That's "woaaah": overly complex - too  
many ways to make a single datagrid.

Let's not forget the "do-it-all" way to make a datagrid: the  
DataGridDataProvider object, which by itself does everything everyone  
would ever wish (or so it seems).

This is just general rant :) - general concerns. I can't suggest anything  
much. Wouldn't it have been better to split this datagrid into multiple  
elements, each being "specialised" for certain use-cases? Not having all  
the use-cases in mind, like now.



That's about all, for now.




[1]  
http://www.whatwg.org/specs/web-apps/current-work/multipage/section-interactive-elements.html#datagrid
[2]  
http://www.whatwg.org/specs/web-apps/current-work/multipage/section-interactive-elements.html#commonDefaultDataGridMethodDefinitions
[3]  
http://www.whatwg.org/specs/web-apps/current-work/multipage/section-interactive-elements.html#populating
[4]  
http://www.whatwg.org/specs/web-apps/current-work/multipage/section-interactive-elements.html#requirements
[5]  
http://www.whatwg.org/specs/web-apps/current-work/multipage/section-interactive-elements.html#cyclecell
[6]  
http://www.whatwg.org/specs/web-apps/current-work/multipage/section-interactive-elements.html#columns


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Received on Tuesday, 11 September 2007 18:34:25 UTC

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