How to add a binding programmatically for a NSTabView? - objective-c

Question

My application contains an NSTabView with two tabs. Further, the application itself has a playState which is an enum. The playState is kept in a Singleton.
typedef enum {
kMyAppPlayStatePlaying,
kMyAppPlayStatePaused
} MyAppPlayState;
The playState gets synthesized here.
#property (readwrite) MyAppPlayState playState;
I want to switch the NSTabView every time the playState changes. Therefore, I prepared an IBOutlet to add a binding similar to this one.
[self.playPauseTabView bind:#"selectedItemIdentifier" toObject:[MyAppState sharedState] withKeyPath:#"playState" options:nil];
I already recognized the identifier must be NSString. This does not match with my enum which is an int. I could maybe use an NSValueTransformer to fix this.
Further, selectedItemIdentifier does not exists. NSTabView only offers selectedTabViewItem which then allows to access identifier or label. Though, I cannot find a way to switch the item itself based on the identifer.

Answer 1

In situations like that, I find myself doing one of two things:
1) Register self (or some other object) as an observer of the property in question, and set the selected tab accordingly in -observeValueForKeyPath:ofObject:change:context:. It could look like this:
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
if ( context == PlayStateChange )
{
if ( [[change objectForKey: NSKeyValueChangeKindKey] integerValue] == NSKeyValueChangeSetting )
{
NSNumber *oldValue = [change objectForKey: NSKeyValueChangeOldKey];
NSNumber *newValue = [change objectForKey: NSKeyValueChangeNewKey];
NSInteger oldInteger = [oldValue integerValue];
NSInteger newInteger = [newValue integerValue];
NSLog(#"Old play state: %ld, new play state: %ld", (long)oldInteger, (long)newInteger);
// Do something useful with the integers here
}
return;
}
}
2) declare a readonly NSString * property and declare that its value is affected by your playState property. Something like this:
#property (readonly) NSString *playStateStr;
// Accessor
-(NSString *)playStateStr
{
return playState == kMyAppPlayStatePlaying ? #"playing" : "paused";
}
+(NSSet *)keyPathsForValuesAffectingPlayStateStr
{
return [NSSet setWithObject: #"playState"];
}
Now you have an NSString-typed property that you can bind your tab view's selection.

Answer 2

I forgot to connect the NSTabView with its IBOutlet in the Interface Builder.
The following works for me.
NSDictionary* playStateOptions = [NSDictionary dictionaryWithObject:[[PlayStateValueTransformer alloc] init] forKey:NSValueTransformerBindingOption];
[self.playPauseTabView bind:#"selectedLabel" toObject:[MyAppState sharedState] withKeyPath:#"playState" options:playStateOptions];
In the NSValueTransformer I return an NSString which must be set in Interface Builder for each tab!