The docs that do exist concerning the way to map arbitrary objects
(such as ones that contain a 'name' attribute in my case) onto text
cells have to do with NSFormatter.
The latter is clearly how one converts 'simple' values from an object
form to a stringified form and v.v.
The problem with using a subclass of NSFormatter in my case is that I
only want to affect a change to the 'name' attribute on an otherwise
persistent object (actually a Core Data object). I don't want to be
creating new 'value' objects every time the user edits a character in
the cell. NSFormatter's getObjectValue:forString:errorDescription:
method is really supposed to return a new object if parsing of the
string is successful.
Nevertheless, it is possible to make a subclass of NSFormatter that is
constructed explicitly to deal with the object that becomes set on the
cell (via setObjectValue:) from the column binding. The
aforementioned method can then forward the received strings to this
object as changes to its name attribute. This is a pretty nasty abuse
of NSFormatter, but it 'works' so long as the object can stomach
'continuous' updates as the user types.
What this doesn't do though, is fix the KVC error mentioned below.
This can be suppressed by implementing -setValue:forUndefinedKey: on
"MyClass" and handling the empty string "key" that gets sent -
essentially to ignore the value (which is curiously the cell's
placeholder string "Text Cell") further indicating that things are
pretty screwed up!
So, I really think there must be a 'proper' way to get the editor to
pick up and return the value (name) I need editing from my cell's
model object, but I'm still searching for the white magic, having
dabbled in the darker sort.
-- Luke
On 30-Jan-09, at 9:32 PM, Luke Evans wrote:
The Cocoa docs seem silent on how to achieve this.
I have an NSTextFieldCell subclass that gets sent an object from
bindings. The reason for sending it an object is that I want the
cell to display a number of the object's attributes - which it does
nicely through custom drawing.
Now I need to allow editing of the text in the cell. I have
overridden:
editWithFrame:inView:editor:delegate:event:
and its buddy:
selectWithFrame:inView:editor:delegate:start:length:
These bring up the text editor nicely. However, as I have an object
at the cell, I need to present a string to this mechanism (the name
property of my object), and similarly I need to somehow obtain the
value from the editor when editing has finished. At the moment, the
default behaviour has the editor coming up with placeholder text,
and when editing is finished I get an KVC error, e.g.:
Error setting value for key path of object <MyClass: 0x1b385c0>
(...) from bound object <NSTableColumn: 0x1b1ab20>(null)): [<MyClass
0x1b385c0> setValue:forUndefinedKey:]: the entity MyClass is not key
value coding-compliant for the key .
Does anyone know how to wire up the editing so that I can provide
initial text to the editor and prevent whoever it is from attempting
to set the final value directly onto the bound object (which it
clearly doesn't know how to do as it's a particular attribute of the
object at the cell)?
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