[Chandler-dev] Dashboard domain model questions

[Bryan Stearns]

[ Oops - a sentence got dropped in the middle there, sorry. ]

Grant Baillie wrote:
>> - there's a list of dependent attributes, allowing us to set up 
>> item/attribute notifications to keep things up to date in the UI. If 
>> we use Calculateds for indexing, we might need the repository to hook 
>> into this so that indexes get updated when dependent attributes 
>> change - we'll talk about this more later.
>
> Interesting: What parts of the UI (tables, attribute editors, ...) set 
> up these notifications?
Block :-)

Any Block that implements onItemNotification, has a viewAttribute 
attribute, and has an item in 'contents', will get that 
onItemNotification method called if the attribute with that name changes 
on that item while the block is rendered. This "viewAttribute on the 
contents item" thing is the default behavior implemented by 
Block.getWatchList; if more attributes (or even attributes on other 
items) need to be watched, the block can override getWatchList to add 
other item/attribute pairs (or replace the list completely).

You can see many of these overrides in Detail.py: this is how, for 
instance, item-dependent visibility is handled (so when you toggle the 
"all day" checkbox, the actual attribute change fires a synchronous 
notification through this mechanism, which notifies the blocks that want 
to show or hide themselves based on the allDay attribute.

Fun fact to know and tell: It turns out that there are seven blocks who 
need to update themselves when allDay changes: the two "time" parts of 
start & end time, the "at" labels before each of them, the status and 
timezone popups (we don't show it for allday events), and the block 
containing the allday label/checkbox itself (which hides itself on 
read-only non-allday events).

Because this mechanism is centralized in Block, there's only one 
repository item-watcher set up, even though there are seven subscribers, 
which reduces overhead for Andi.

One caveat: Be careful not to change attribute values in your 
onItemNotification method, unless you want to spend forever there.

...Bryan