objective c - Set NSButton enabled based on NSArrayController selection -

ok, i've set nstableview bound nsarraycontroller.

now, have nsbutton want make "enabled" when there is selection, , disabled when there nothing selected.

so, i'm bind nsbutton's enabled array controller's selection value transformer of nsisnotnil.

however, doesn't seem working.

am missing anything?

regardless of whether or not selected, selection property of nsarraycontroller returns object (_nscontrollerproxyobject). why binding isn't working way expect, because selection never nil. instead, bind selectionindexes, rather selection, , have value transformer called selectionindexescountiszero implemented so:

@interface selectionindexescountiszero : nsvaluetransformer @end  @implementation selectionindexescountiszero  + (class)transformedvalueclass { return [nsnumber class]; }  + (bool)allowsreversetransformation { return no; }  - (id)transformedvalue:(nsindexset *)value { return [nsnumber numberwithbool:[value count] > 0]; }  @end 

incidentally, can still bind selection if wish, require custom value transformer. apple state that: if value requested selection proxy [object] using key-value coding returns multiple objects, controller has no selection, or proxy not key-value coding compliant requested key, appropriate marker returned. in other words, find out if there in fact no selection, need (i) access proxy object, (ii) call 1 of methods of actual objects, , (iii) test see if return value (ii) nsnoselectionmarker. doing way key method of value transformer this:

- (id)transformedvalue:(id)selectionproxyobject {     // assume objects in table team objects, 'name' property     return [selectionproxyobject valueforkeypath:@"name"] == nsnoselectionmarker ? @yes : @no; } 

selectionindexes better way since generic. in fact, if sort of thing lot can idea build transformer library, can import project. here names of of transformers in library:

selectionindexescountiszero selectionindexescountisexactlyone selectionindexescountisoneorgreater selectionindexescountisgreaterthanone // ...you picture