When does objectValueForTableColumn: get called? - objective-c

Question

I am currently going through the 3rd Edition of the Mac OSX Cocoa book from the Big Nerd Ranch guys and I am editing my program to include table views. Here the code from the AppController.m file where I have to implement the required protocol methods from the TableView:
-(id)init{
self = [super init];
voiceArray = [NSSpeechSynthesizer availableVoices];
speechSynth = [[NSSpeechSynthesizer alloc] initWithVoice:nil];
[speechSynth setDelegate:self];
return self;
}
-(int)numberOfRowsInTableView:(NSTableView *)tv{
NSLog(#"Getting number of rows in table view: %lu", [voiceArray count]);
return [voiceArray count];
}
-(id)tableView:(NSTableView *)tv objectValueForTableColumn:(NSTableColumn *)tableColumn row:(NSInteger)row{
NSString *v = [voiceArray objectAtIndex:row];
NSDictionary *dict = [NSSpeechSynthesizer attributesForVoice:v];
NSLog(#"Voice Name %#", [dict objectForKey:NSVoiceName]);
return [dict objectForKey:NSVoiceName];
}
-(void)tableViewSelectionDidChange:(NSNotification *)notification{
int row = [tableView selectedRow];
NSLog(#"row selected %d", row);
if(row == 1){
return;
}
NSString *selectedVoice = [voiceArray objectAtIndex:row];
[speechSynth setVoice:selectedVoice];
NSLog(#"new voice %# ", selectedVoice);
}
When the app first loads I get the following output:
2012-05-27 15:02:29.040 Speakline[42836:f03] Getting number of rows in
table view: 24 2012-05-27 15:02:29.042 Speakline[42836:f03] row
selected 2 2012-05-27 15:02:29.043 Speakline[42836:f03] new voice
com.apple.speech.synthesis.voice.Alex 2012-05-27 15:02:29.162
Speakline[42836:f03] Voice Name Agnes 2012-05-27 15:02:29.163
Speakline[42836:f03] Voice Name Albert
I want to make sure I understand fully what is going on here. In order to do this I have a couple of questions.
It looks like the numberOfRowsInTableView: method was automatically called after the init method. Is this correct?
How often does objectValueForTableColumn: get called? What events prompt that method to get called? Also, in the code there, the return statement confused me. Where exactly does this return value go?
As a side note they wanted me to connect the Outlets and the AppController via control+clicking (via the connections panel) and linking them in that way. What alternatives are there avaialble for connecting delegates and datasources to different kinds of views without doing this? I am assuming that adding NSTableViewDelegate in the controller header file might be one way. If you have the option of control+click connecting all your views to outlets and so on vs programmatically setting it all up is it just a matter of preference at this point? It just seems to me that in order to understand what is going on it might be better to just write the code yourself.

Answer 1

1) Both numberOfRowsInTableView and objectValueForTableColumn:Row: get called soon after the nib is unarchived (I'm not sure of the exact order of things), so the table view can be populated with data.
2) The loading of the table and reloading or adding new data as well as scrolling will cause objectValueForTableColumn:row: to be called (by the table view). It gets called for each row that is populated. The value goes to the table view, that's how it gets its data.
3) The other way to connect delegates is to do it in code with setDelegate:, but putting NSTableViewDelegate in the .h file does not do that -- that's just a promise to the compiler that you will implement some or all of the delegate messages.