On Fri, Aug 8, 2008 at 9:52 AM, Johannes Fahrenkrug
<email@hidden> wrote:
> I'd like to display placeholder images until the table cell gets
> displayed and then load the actual thumbnail, replacing the
> placeholder image with the real thumbnail once it has loaded.
> What would be the best way to do this? I'm thinking of something on
> the lines of a proxy object...
Are you using the NSTableView data source API? I think that would be
easier for what you want to do. I'd create a placeholder NSImage at
first, and when I'm asked for the data for my NSImage column, if I
haven't yet finished downloading the image for that particular row,
give the NSTableView my placeholder image. Then, once the image has
finished downloading, call [myTableView
setNeedsDisplayInRect:NSIntersectionRect([myTableView
rectForColumn:indexOfImageColumn], [myTableView
rectForRow:rowOfUpdatedItem])].
Remember that the rows of an NSTableView don't actually exist as one
large dataset, so there isn't a one-to-one table cell to NSCell
correspondence. Instead, each NSTableColumn has its own cell, that it
uses like a rubber stamp. When a region of the table is marked as
dirty (setNeedsDisplay:/setNeedsDisplayInRect:), the table view
figures out which columns are affected, and tells them to draw
themselves. Each column then asks for the data for each table cell
that needs to be redrawn, and passes this value off to the NSCell
assigned to that column, which does the real drawing.
So your image column has an NSImageCell. When you start scrolling,
the NSTableView figures out which logical row and column numbers have
just been revealed by your scrolling maneuver, and kicks off the above
process. Your data source is asked "alright, row 12 column 2 needs to
be painted, gimme the data", and then hands that data off to the cell
belonging to the column. The dirty little secret is that from the
table view's perspective, there aren't actually any rows at all; it
just does a bunch of math based on where the scroll point is located
to convert graphics coordinates to logical rows. Your data source is
none the wiser.
--Kyle Sluder
_______________________________________________
Cocoa-dev mailing list (email@hidden)
Please do not post admin requests or moderator comments to the list.
Contact the moderators at cocoa-dev-admins(at)lists.apple.com
Help/Unsubscribe/Update your Subscription:
http://lists.apple.com/mailman/options/cocoa-dev/email@hidden
This email sent to email@hidden
